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ltc3576/ltc3576-1 1 3576fb typical application features applications description switching power manager with usb on-the-go + triple step-down dc/dcs n hdd-based media players n gps, pdas, digital cameras, smart phones n automotive compatible portable electronics l , lt, ltc, ltm, linear technology and the linear logo are registered trademarks of linear technology corporation. bat-track and powerpath are trademarks of linear technology corporation. all other trademarks are the property of their respective owners. protected by u.s. patents, including 6522118, 6404251. high ef? ciency powerpath manager with overvoltage protection and triple step-down regulator powerpath switching regulator ef? ciency to system load (p vout /p vbus ) n bidirectional switching regulator with bat-track? adaptive output control provides ef? cient charging and a 5v output for usb on-the-go n bat-track control of external high voltage step- down switching regulator n overvoltage protection guards against damage n instant-on operation with discharged battery n triple step-down switching regulators with i 2 c adjustable outputs (1a/400ma/400ma i out ) n 180m internal ideal diode + external ideal diode controller powers the load in battery mode n li-ion/polymer battery charger (1.5a max i chg ) n battery float voltage: 4.2v (ltc3576), 4.1v (ltc3576-1) n compact (4mm 6mm 0.75mm) 38-pin qfn package the ltc ? 3576/ltc3576-1 are highly integrated power management and battery charger ics for li-ion/polymer battery applications. they each include a high ef? ciency, bidirectional switching powerpath? manager with auto- matic load prioritization, a battery charger, an ideal diode, a controller for an external high voltage switching regulator and three general purpose step-down switching regulators with i 2 c adjustable output voltages. the internal switch- ing regulators automatically limit input current for usb compatibility and can also generate 5v at 500ma for usb on-the-go applications when powered from the battery. both the usb and external switching regulator power paths feature bat-track optimized charging to provide maximum power to the application from supplies as high as 38v. an overvoltage circuit protects the ltc3576/ltc3576-1 from damage due to high voltage on the v bus or wall pins with just two external components. the ltc3576/ltc3576-1 are available in a low pro? le 38-pin (4mm 6mm 0.75mm) qfn package. li-ion 0.8v to 3.6v/400ma 3.3v/20ma 0.8v to 3.6v/400ma 0.8v to 3.6v/1a rst 2 optional 0v t to other loads + ltc3576/ltc3576-1 triple high efficiency step-down switching regulators i 2 c port always on ldo memory rtc/low power logic i 2 c core i/o 3576 ta01 processor charge enable controls usb compliant bidirectional switching regulator overvoltage protection external high voltage buck controller cc/cv battery charger 6 1 2 3 usb or 5v ac adapter automotive firewire, etc. lt3653 load current (ma) 10 0 efficiency (%) 20 40 60 80 100 1000 3576 ta01b 100 10 30 50 70 90 bat = 4.2v bat = 3.3v v bus = 5v i bat = 0ma 10x mode
ltc3576/ltc3576-1 2 3576fb pin configuration absolute maximum ratings v bus , wall (transient) t < 1ms, duty cycle < 1% .......................................... ?0.3v to 7v v bus , wall (static), bat, v in1 , v in2 , v in3 , v out , enotg, ntc, sda, scl, dv cc , rst3 chrg 3 t 3 t s t at 3 3 3 t t 3 3 3 t 3 ss a cprg 3a chrg rst3 a prg a 33 3a sw sw cti a sw sw3 at t cti a i ti teertre c erti teertre re c t c stre teertre re c t c te 3 3 tp w 3 pacag 3a s 6mm) plastic qfn 17 18 19 38 37 36 35 34 33 32 24 25 26 27 28 29 30 31 8 7 6 5 4 3 2 1clprog ldo3v3 ntcbias ntc ovgate ovsens fb1 v in1 sw1 en1 enotg dv cc idgate chrg prg acpr wa c sw rst3 3 sw s s t at sc sa c 3 sw3 c 3 3 t a c a 3cw ps pa p 3 s g st sr t pc s paratr cts tp a ts pwerpt switi retrstew e s t s te 3 s tt t crret e e e w pwer se e hi pwer se e 3 3 a a a a a s te t ieet crret e e whi pwer se e a a a rr rat a r sh tap a r part arg pacag scrpt tpratr rag tc3p tc3trp 3 3e pti c t c tc3p tc3trp 3 3e pti c t c ct tc reti r rt ei e wit wier erti teertre re ct tc reti r irti tr e e i rt r re irti e ree rt ri t ttwwwiereree r re irti te ree ei ti t ttwwwierteree ctrca charactrstcs te ete te ei ti wi er te erti teertre re terwie ei ti re t t a c s at 3 cc 33 r cprg 3 e terwie te
ltc3576/ltc3576-1 3 3576fb electrical characteristics the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v bus = 5v, bat = 3.8v, dv cc = 3.3v, r clprog = 3.01k, unless otherwise noted. symbol parameter conditions min typ max units h clprog (note 4) ratio of measured v bus current to clprog program current 1 mode 5 mode 10 mode low power suspend mode high power suspend mode 210 1160 2200 9.6 56 ma/ma ma/ma ma/ma ma/ma ma/ma i vout(powerpath) v out current available before discharging battery 1 mode, bat = 3.3v 5 mode, bat = 3.3v 10 mode, bat = 3.3v low power suspend mode high power suspend mode 0.26 1.6 121 667 1217 0.31 2 0.41 2.4 ma ma ma ma ma v clprog clprog servo voltage in current limit switching modes suspend modes 1.18 100 v mv v uvlo v bus undervoltage lockout rising threshold falling threshold 3.95 4.30 4.00 4.35 v v v duvlo v bus to bat differential undervoltage lockout rising threshold falling threshold 200 50 mv mv v out v out voltage 1 , 5 , 10 modes, 0v < bat < 4.2v, i vout = 0ma, battery charger off usb suspend modes, i vout = 250a 3.4 4.5 bat + 0.3 4.6 4.7 4.7 v v f osc switching frequency 1.8 2.25 2.7 mhz r pmos_ powerpath pmos on-resistance 0.18 r nmos_ powerpath nmos on-resistance 0.30 i peak_powerpath peak inductor current limit 1 mode (note 5) 5 mode (note 5) 10 mode (note 5) 1 2 3 a a a r susp suspend ldo output resistance closed loop 10 powerpath switching regulatorstep-up mode (usb on-the-go) v bus output voltage 0ma i vbus 500ma, v out > 3.2v 4.75 5.25 v v out input voltage 2.9 5.5 v i vbus output current limit l 550 680 ma i peak peak inductor current limit (note 5) 1.8 a i otgq v out quiescent current v out = 3.8v, i vbus = 0ma (note 6) 1.38 ma v clprog output current limit servo voltage 1.15 v v out(uvlo) v out uvlov out falling v out uvlov out rising 2.5 2.6 2.8 2.9 v v t scfault short-circuit fault delay v bus < 4v and pmos switch off 7.2 ms bat-track switching regulator control v wall absolute wall input threshold rising threshold hysteresis 4.2 4.3 1.1 4.4 v v v wall differential wall input threshold wall-bat falling hysteresis 030 60 45 mv mv v out regulation target under v c control 3.55 bat + 0.3 v i wallq wall quiescent current 400 a r acpr acpr pull-down strength 150 v h acpr acpr high voltage v out v v l acpr acpr low voltage 0v
ltc3576/ltc3576-1 4 3576fb electrical characteristics the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v bus = 5v, bat = 3.8v, dv cc = 3.3v, r clprog = 3.01k, unless otherwise noted. symbol parameter conditions min typ max units overvoltage protection v ovcutoff overvoltage protection threshold with 6.2k series resistor 6.1 6.35 6.7 v v ovgate ovgate output voltage v ovsens < v ovcutoff v ovsens > v ovcutoff 1.88?v ovsens 0 12 v v t rise ovgate time to reach regulation ovgate c load = 1nf 2.2 ms battery charger v float bat regulated output voltage ltc3576 l 4.179 4.165 4.200 4.200 4.221 4.235 v v ltc3576-1 l 4.079 4.065 4.100 4.100 4.121 4.135 v v i chg constant current mode charger current r prog = 1k r prog = 5k 980 185 1030 206 1065 223 ma ma i bat battery drain current v bus > v uvlo , suspend mode, i vout = 0a 3.6 6 a v bus = 0v, i vout = 0a (ideal diode mode) 28 45 a v prog prog pin servo voltage 1.000 v v prog_trkl prog pin servo voltage in trickle charge bat < v trkl 0.100 v v c/10 c/10 threshold voltage at prog 100 mv h prog ratio of i bat to prog pin current 1030 ma/ma i trkl trickle charge current bat < v trkl , r prog = 1k 100 ma v trkl trickle charge threshold voltage bat rising 2.7 2.85 3.0 v v trkl trickle charge hysteresis voltage 135 mv v rechrg recharge battery threshold voltage threshold voltage relative to v float C75 C100 C125 mv t term safety timer termination period timer starts when v bat = v float 3.3 4 5 hour t badbat bad battery termination time bat < v trkl 0.4 0.5 0.6 hour h c/10 end of charge current ratio (note 7) 0.085 0.1 0.112 ma/ma v chrg chrg pin output low voltage i chrg = 5ma 65 100 mv i chrg chrg pin leakage current v chrg = 5v 1 a r on_chg battery charger power fet on- resistance (between v out and bat) 0.18 t lim junction temperature in constant temperature mode 110 c ntc v cold cold temperature fault threshold voltage rising threshold hysteresis 75 76.5 1.6 78 %ntcbias %ntcbias v hot hot temperature fault threshold voltage falling threshold hysteresis 33.4 34.9 1.5 36.4 %ntcbias %ntcbias v dis ntc disable threshold voltage falling threshold hysteresis 0.7 1.7 50 2.7 %ntcbias mv i ntc ntc leakage current ntc = ntcbias = 5v C50 50 na ideal diode v fwd forward voltage i vout = 10ma 15 mv r dropout internal diode on-resistance dropout i vout = 200ma 0.18 i max_diode diode current limit 2 a
ltc3576/ltc3576-1 5 3576fb electrical characteristics the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v bus = 5v, bat = 3.8v, dv cc = 3.3v, r clprog = 3.01k, unless otherwise noted. symbol parameter conditions min typ max units always on 3.3v ldo supply v ldo3v3 regulated output voltage 0ma < i ldo3v3 < 20ma 3.1 3.3 3.5 v r cl_ldo3v3 closed-loop output resistance 2.7 r ol_ldo3v3 dropout output resistance 23 logic (i lim0 , i lim1 , en1, en2, en3, enotg, and scl, sda when dv cc = 0v) v il logic low input voltage 0.4 v v ih logic high input voltage 1.2 v i pd1 i lim0 , i lim1 , en1, en2, en3, enotg, scl, sda pull-down current 2a i 2 c port dv cc input supply 1.6 5.5 v i dvcc dv cc current scl/sda = 0khz, dv cc = 3.3v 0.5 a v dvcc(uvlo) dv cc uvlo 1.0 v address i 2 c address 0001001[0] v ih , sda, scl input high threshold 70 %dv cc v il , sda, scl input low threshold 30 %dv cc i pd2 , sda, scl pull-down current 2a v ol digital output low (sda) i sda = 3ma 0.4 v f scl clock operating frequency 400 khz t buf bus free time between stop and start condition 1.3 s t hd_sta hold time after (repeated) start condition 0.6 s t su_sta repeated start condition setup time 0.6 s t su_sto stop condition setup time 0.6 s t hd_dat(o) data hold time output 0 900 ns t hd_dat(i) data hold time input 0 ns t su_dat data setup time 100 ns t low scl low period 1.3 s t high scl high period 0.6 s t f sda/scl fall time 20 300 ns t r sda/scl rise time 20 300 ns t sp input spike suppression pulse width 50 ns general purpose switching regulators 1, 2 and 3 v in1,2,3 input supply voltage (note 8) 2.7 5.5 v v out(uvlo) v out uvlov out falling v out uvlov out rising v in1,2,3 connected to v out through low impedance. switching regulators are disabled in uvlo 2.5 2.6 2.8 2.9 v v f osc switching frequency 1.8 2.25 2.7 mhz i fb1,2,3 fbx input current v fb1,2,3 = 0.85v C50 50 na d1,2,3 maximum duty cycle 100 % r sw1,2,3_pd swx pull-down in shutdown 10 k
ltc3576/ltc3576-1 6 3576fb electrical characteristics the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v bus = 5v, bat = 3.8v, dv cc = 3.3v, r clprog = 3.01k, unless otherwise noted. symbol parameter conditions min typ max units i vin1,2,3 pulse-skipping mode input current i out1,2,3 = 0a (note 9) 90 a burst mode ? input current i out1,2,3 = 0a (note 9) 20 35 a ldo mode input current i out1,2,3 = 0a (note 9) 15 25 a shutdown input current limit i out1,2,3 = 0a, fb1,2,3 = 0v 1 a v fbhigh1,2,3 maximum servo voltage full scale (1,1,1,1) (note 10) l 0.78 0.80 0.82 v v fblow1,2,3 minimum servo voltage zero scale (0,0,0,0) (note 10) 0.405 0.425 0.445 v v lsb1,2,3 v fb1,2 servo voltage step size 25 mv r ldo_cl1,2,3 ldo mode closed-loop r out v fb1,2,3 = v out1,2 3 = 0.8v 0.25 r ldo_ol1,2,3 ldo mode open-loop r out (note 11) 2.5 general purpose switching regulator 1 and 2 i lim1,2 pmos switch current limit pulse-skipping/burst mode operation (note 5) 600 900 1300 ma i out1,2 available output current ldo mode 50 ma r p1,2 pmos r ds(on) 0.6 r n1,2 nmos r ds(on) 0.7 general purpose switching regulator 3 i lim3 pmos switch current limit pulse-skipping/burst mode operation (note 5) 1300 1800 2800 ma i out3 available output current ldo mode 50 ma r p3 pmos r ds(0n) 0.18 r n3 nmos r ds(on) 0.3 t rst3 power-on reset time for switching regulator v fb3 within 92% of final value to rst3 hi-z 230 ms burst mode is a registered trademark of linear technology corporation. note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: the ltc3576e/ltc3576e-1 are guaranteed to meet performance speci? cations from 0c to 85c. speci? cations over the C40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 3: the ltc3576e/ltc3576e-1 include overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperature will exceed 125c when overtemperature protection is active. continuous operation above the speci? ed maximum operating junction temperature may impair device reliability. note 4: total input current is the sum of quiescent current, i vbusq , and measured current given by v clprog /r clprog ? (h clprog + 1). note 5: the current limit features of this part are intended to protect the ic from short term or intermittent fault conditions. continuous operation above the maximum speci? ed pin current rating may result in device degradation or failure. note 6: the bidirectional switchers supply current is bootstrapped to v bus and in the application will re? ect back to v out by (v bus /v out ) ? 1/ef? ciency. total quiescent current is the sum of the current into the v out pin plus the re? ected current. note 7: h c/10 is expressed as a fraction of the measured full charge current with indicated prog resistor. note 8: v out not in uvlo. note 9: fbx above regulation such that regulator is in sleep. speci? cation does not include resistive divider current re? ected back to v inx . note 10: applies to pulse-skipping and burst mode operation only. note 11: inductor series resistance adds to open-loop r out .
ltc3576/ltc3576-1 7 3576fb typical performance characteristics ideal diode v-i characteristics ideal diode resistance vs battery voltage v out voltage vs load current (battery charger disabled) usb limited load current vs battery voltage (battery charger disabled) battery and v bus currents vs load current battery charge current vs temperature powerpath switching regulator transient response powerpath switching regulator ef? ciency vs load current battery charging ef? ciency vs battery voltage with no external load (p bat /p vbus ) forward voltage (v) 0 current (a) 0.6 0.8 1.0 0.16 3576 g01 0.4 0.2 0 0.04 0.08 0.12 0.20 internal ideal diode with supplemental external vishay si2333 pmos internal ideal diode only v bus = 5v battery voltage (v) 2.7 resistance () 0.15 0.20 0.25 3.9 3576 g02 0.10 0.05 0 3.0 3.3 3.6 4.2 internal ideal diode with supplemental external vishay si2333 pmos internal ideal diode temperature (c) C40 0 charge current (ma) 100 200 300 400 040 80 120 3576 g06 500 600 C20 20 60 100 thermal regulation r prog = 2k load current (a) 0 v out (v) 4.00 4.25 4.50 0.8 3576 g03 3.75 3.50 3.25 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.9 1.0 bat = 4v bat = 3.4v battery voltage (v) 2.7 0 load current (ma) 100 300 400 500 3.3 3.9 4.2 900 3576 g04 200 3.0 3.6 600 700 800 v bus = 5v 5 s mode load current (ma) 0 current (ma) 250 500 750 800 3576 g05 0 C250 C500 100 200 300 400 500 600 700 900 1000 v bus current battery current (charging) v bus = 5v bat = 3.8v 5 s mode r clprog = 3.01k r prog = 1k battery current (discharging) v out 50mv/div ac coupled i vout 500ma/div 0ma 20s/div 3576 g07 v bus = 5v v out = 3.65v charger off 10 s mode load current (ma) 30 60 50 40 100 90 80 70 3576 g08 efficiency (%) 10 1000 100 1 s mode 5 s , 10 s mode battery voltage (v) 2.7 50 efficiency (%) 55 65 70 75 3.3 3.9 4.2 95 3576 g09 60 3.0 3.6 80 85 90 r clprog = 3.01k r prog = 1k 1 s mode 5 s mode t a = 25c unless otherwise speci? ed.
ltc3576/ltc3576-1 8 3576fb v bus quiescent current vs v bus voltage (suspend) v out voltage vs load current in suspend v bus current vs load current in suspend battery charge current vs v out voltage normalized battery charger float voltage vs temperature v out voltage vs battery voltage (charger overprogrammed) v bus quiescent current vs temperature battery drain current vs temperature v bus quiescent current in suspend vs temperature bus voltage (v) 0 0 quiescent current (a) 10 20 30 40 50 60 1234 3576 g10 5 load current (ma) 0 v out (v) 4.0 4.5 5.0 2.0 3576 g11 3.5 3.0 2.5 0.5 1.0 1.5 2.5 high power suspend low power suspend v bus = 5v bat = 3.3v r clprog = 3.01k load current (ma) 0 v bus current (ma) 1.5 2.0 2.5 2.0 3576 g12 1.0 0.5 0 0.5 1.0 1.5 2.5 high power suspend low power suspend v bus = 5v bat = 3.3v r clprog = 3.01k v out (v) 3.40 0 battery current (ma) 100 200 300 400 3.50 3.60 3.70 3.80 3576 g13 500 600 3.45 3.55 3.65 3.75 r clprog = 3.01k r prog = 2k 5 s mode battery voltage (v) 2.7 v out (v) 3.9 4.3 4.7 3.9 3576 g14 3.5 3.1 3.7 4.1 4.5 3.3 2.9 2.7 3.0 3.3 3.6 4.2 5 s mode 1 s mode v bus = 5v i vout = 0v r clprog = 3.01k r prog = 1k temperature (c) C40 normalized float voltage 0.998 0.999 1.000 60 3576 g15 0.997 0.996 C15 10 35 85 1.001 temperature (c) C40 quiescent current (ma) 15 20 25 60 3576 g16 10 5 0 C15 10 35 85 v bus = 5v 5 s mode 1 s mode temperature (c) C40 0 quiescent current (a) 10 20 30 40 50 60 C15 10 35 60 3576 g17 85 v bus = 5v temperature (c) C40 25 30 35 60 3576 g18 20 15 C15 10 35 85 10 5 0 battery current (a) bat = 3.8v v bus = 0v switching regulators off typical performance characteristics t a = 25c unless otherwise speci? ed.
ltc3576/ltc3576-1 9 3576fb otg boost quiescent current vs v out voltage otg boost v bus voltage vs load current otg boost ef? ciency vs load current otg boost ef? ciency vs v out voltage otg boost start-up time into current source load vs v out voltage otg boost burst mode operation otg boost transient response otg boost burst mode current threshold vs v out voltage otg boost start-up into current source load v out (v) 2.90 0.5 quiescent current (ma) 0.7 1.1 1.3 1.5 2.5 1.9 3.55 4.20 3576 g19 0.9 2.1 2.3 1.7 4.85 5.50 load current (ma) 0 100 3.0 v bus (v) 4.0 5.5 200 400 500 3576 g20 3.5 5.0 4.5 300 600 700 v out = 5v v out = 4.4v v out = 3.8v v out = 3.2v v bus = 4.75v i vbus = 500ma load current (ma) 1 40 efficiency (%) 80 90 100 10 100 1000 3576 g21 70 60 50 v out = 5v v out = 4.4v v out = 3.8v v out = 3.2v v out (v) 2.90 efficiency (%) 80 85 5.50 3576 g22 75 70 3.55 4.20 4.85 95 90 500ma load 100ma load v out (v) 2.9 1.50 time (ms) 1.75 2.00 2.25 2.50 3.4 3.9 4.4 4.9 3576 g23 5.4 22f on v bus , 22f and load through ovp 22f on v bus , no ovp 22f on v bus , load through ovp v out (v) 2.90 load current (ma) 200 300 5.50 3576 g24 100 0 3.55 4.20 4.85 400 rising threshold falling threshold v bus 50mv/div ac coupled i vbus 200ma/div 0ma 20s/div 3576 g25 v out = 3.8v i vbus 200ma/div v bus 2v/div 0v 0ma 200s/div 3576 g26 v out = 3.8v i load = 500ma v bus 50mv/div ac coupled v sw 1v/div 0v 50s/div v out = 3.8v i load = 10ma 3576 g27 typical performance characteristics t a = 25c unless otherwise speci? ed.
ltc3576/ltc3576-1 10 3576fb battery charging from usb-hv buck-usb usb otg from bat-hv buck-bat oscillator frequency vs temperature ovp connect waveform ovp disconnect waveform rising ovp threshold vs temperature ovgate vs ovsens ovgate quiescent current vs temperature rst3 , chrg pin current vs voltage (pull-down state) v out 1v/div ac coupled v bus 100mv/div ac coupled v sw 5v/div hvok 5v/div 0v 0v 500s/div 3576 g28 v bus = 5v hv in = 12v using lt3653 v out 1v/div ac coupled v bus 200mv/div ac coupled i bat 1a/div hvok 5v/div 0v 500s/div 3576 g29 v bat = 3.8v i bus = 285ma hv in = 12v using lt3653 0a temperature (c) C40 frequency (mhz) 2.20 2.25 2.30 60 3576 g30 2.15 2.10 2.05 C15 10 35 85 v out = 5v v out = 4.2v v out = 3.6v v out = 3v v out = 2.7v v bus 5v/div ovgate 5v/div 500s/div 3576 g31 ovp input voltage 0v to 5v step 5v/div v bus 5v/div ovgate 5v/div 500s/div 3576 g32 ovp input voltage 5v to 10v step 5v/div temperature (c) C40 ovp threshold (v) 6.270 6.275 6.280 60 3576 g33 6.265 6.260 6.255 C15 10 35 85 input voltage (v) 0 0 ovgate (v) 2 4 6 8 10 12 24 68 3576 g34 ovsens connected to input through 6.2k resistor temperature (c) C40 quiescent current (a) 33 35 37 60 3576 g35 31 29 27 C15 10 35 85 v ovsens = 5v rst3 , chrg pin voltage (v) 0 rst3 , chrg pin current (ma) 60 80 100 4 3576 g36 40 20 0 1 2 3 5 v bus = 5v bat = 3.8v typical performance characteristics t a = 25c unless otherwise speci? ed.
ltc3576/ltc3576-1 11 3576fb 3.3v ldo output voltage vs load current, v bus = 0v 3.3v ldo step response (5ma to 15ma) battery drain current vs battery voltage switching regulator low power quiescent currents vs temperature switching regulator current limit vs temperature r ds(on) for switching regulator power switches vs temperature switching regulators 1, 2 pulse-skipping mode ef? ciency switching regulators 1, 2 burst mode ef? ciency load current (ma) 0 output voltage (v) 3.0 3.2 20 3576 g37 2.8 2.6 5 10 15 25 3.4 bat = 3.9v, 4.2v bat = 3.6v bat = 3v bat = 3.5v bat = 3.4v bat = 3.1v bat = 3.2v bat = 3.3v i ldo3v3 5ma/div 0ma 20s/div bat = 3.8v 3576 g38 v ldo3v3 20mv/div ac coupled battery voltage (v) 2.7 25 30 35 3.9 3576 g39 20 15 3.0 3.3 3.6 4.2 10 5 0 battery current (a) i vout = 0ma v bus = 0v v bus = 5v (suspend mode) switching regulator soft-start waveform v out 500mv/div 50s/div 3576 g40 temperature (c) C40 current limit (a) 1.0 1.5 60 3576 g41 0.5 0 C15 10 35 85 2.0 regulator 3 regulators 1, 2 v in1,2,3 = 3.8v temperature (c) C40 on-resistance () 0.6 0.8 1.0 60 3576 g42 0.4 0.2 0 C15 10 35 85 nmos switch nmos switch pmos switch regulators 1, 2 regulator 3 pmos switch temperature (c) C40 quiescent currents (a) 60 80 100 60 3576 g43 40 20 50 70 90 30 10 0 C15 10 35 85 burst mode operation pulse-skipping mode ldo mode load current (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3576 g44 0 1 v in3 = 3.8v v out1,2 = 2.5v v out1,2 = 1.2v v out1,2 = 1.8v load current (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3576 g45 0 1 v in3 = 3.8v v out1,2 = 2.5v v out1,2 = 1.2v v out1,2 = 1.8v typical performance characteristics t a = 25c unless otherwise speci? ed.
ltc3576/ltc3576-1 12 3576fb switching regulator constant frequency quiescent currents switching regulator 3 pulse-skipping mode ef? ciency switching regulator 3 burst mode ef? ciency switching regulators 1, 2 feedback voltage vs load current switching regulators 1, 2 transient response switching regulator mode transition, pulse-skipping-ldo- pulse-skipping switching regulator 3 feedback voltage vs load current switching regulator 3 transient response switching regulator mode transition, pulse-skippingCburst mode operationCpulse-skipping temperature (c) C40 quiescent current (ma) 3 4 5 35 85 3576 g46 2 1 0 C15 10 60 6 7 8 switching regulator 3 switching regulators 1, 2 load current (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3576 g47 0 1 v in3 = 3.8v v out3 = 2.5v v out3 = 1.2v v out3 = 1.8v load current (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3576 g48 0 1 v in3 = 3.8v v out3 = 2.5v v out3 = 1.2v v out3 = 1.8v load current (ma) 0.800 feedback voltage (v) 0.810 0.820 0.795 0.805 0.815 0.1 10 100 1000 3576 g49 0.790 1 burst mode operation pulse-skipping mode v out2 50mv/div ac coupled i out2 200ma/div 0ma 50s/div 3576 g50 v in2 = 3.8v v out2 = 3.4v v out3 50mv/div ac coupled v sw3 1v/div 0v 50s/div 3576 g51 v in3 = 3.8v v out3 = 1.8v i out3 = 50ma load current (ma) 0.795 feedback voltage (v) 0.800 0.805 0.810 0.1 10 100 1000 3576 g52 0.790 1 burst mode operation pulse-skipping mode v out3 50mv/div ac coupled i out3 500ma/div 0ma 50s/div 3576 g53 v in3 = 3.8v v out3 = 1.8v v out3 50mv/div ac coupled v sw3 1v/div 0v 50s/div 3576 g54 v in3 = 3.8v v out3 = 1.8v i out3 = 100ma typical performance characteristics t a = 25c unless otherwise speci? ed.
ltc3576/ltc3576-1 13 3576fb pin functions clprog (pin 1): usb current limit program and monitor pin. a 1% resistor from clprog to ground determines the upper limit of the current drawn or sourced from the v bus pins. a precise fraction, h clprog , of the v bus cur- rent is sent to the clprog pin when the pmos switch of the powerpath switching regulator is on. the switching regulator delivers power until the clprog pin reaches 1.18v in step-down mode and 1.15v in step-up mode. when the switching regulator is in step-down mode, clprog is used to regulate the average input current. several v bus current limit settings are available via user input which will typically correspond to the 500ma and 100ma usb speci? cations. when the switching regulator is in step-up mode (usb on-the-go), clprog is used to limit the average output current to 680ma. a multilayer ceramic averaging capacitor or r-c network is required at clprog for ? ltering. ldo3v3 (pin 2): 3.3v ldo output pin. this pin provides a regulated always-on 3.3v supply voltage. ldo3v3 gets its power from v out . it may be used for light loads such as a watchdog microprocessor or real time clock. a 1f capacitor is required from ldo3v3 to ground. if the ldo3v3 output is not used it should be disabled by connecting it to v out . ntcbias (pin 3): ntc thermistor bias output. if ntc operation is desired, connect a bias resistor between ntcbias and ntc, and an ntc thermistor between ntc and gnd. to disable ntc operation, connect ntc to gnd and leave ntcbias open. ntc (pin 4): input to the thermistor monitoring circuits. the ntc pin connects to a negative temperature coef? cient thermistor, which is typically co-packaged with the battery, to determine if the battery is too hot or too cold to charge. if the batterys temperature is out of range, charging is paused until it re-enters the valid range. a low drift bias resistor is required from ntcbias to ntc and a thermistor is required from ntc to ground. to disable ntc operation, connect ntc to gnd and leave ntcbias open. ovgate (pin 5): overvoltage protection gate output. connect ovgate to the gate pin of an external n-channel mos pass transistor. the source of the transistor should be connected to v bus and the drain should be connected to the products dc input connector. in the absence of an overvoltage condition, this pin is connected to an internal charge pump capable of creating suf? cient overdrive to fully enhance the pass transistor. if an overvoltage condition is detected, ovgate is brought rapidly to gnd to prevent damage to the ltc3576/ltc3576-1. ovgate works in conjunction with ovsens to provide this protection. ovsens (pin 6): overvoltage protection sense input. ovsens should be connected through a 6.2k resistor to the input power connector and the drain of an external n-channel mos pass transistor. when the voltage on this pin exceeds v ovcutoff , the ovgate pin will be pulled to gnd to disable the pass transistor and protect the ltc3576/ltc3576-1. the ovsens pin shunts current during an overvoltage transient in order to keep the pin voltage at 6v. fb1 (pin 7): feedback input for switching regulator 1. when regulator 1s control loop is complete, this pin servos to 1 of 16 possible set points based on the commanded value from the i 2 c serial port. see table 4. v in1 (pin 8): power input for switching regulator 1. this pin will generally be connected to v out . a 1f mlcc capacitor is recommended on this pin. sw1 (pin 9): power transmission pin for switching regulator 1. en1 (pin 10): logic input. this logic input pin indepen- dently enables switching regulator 1. active high. this pin is logically ored with its corresponding bit in the i 2 c serial port. see table 3. has a 2a internal pull-down current source. enotg (pin 11): logic input. this logic input pin inde- pendently enables the bidirectional switching regulator to step up the voltage on v out and provide a 5v output on v bus for usb on-the-go applications. active high. this pin is logically ored with its corresponding bit in the i 2 c serial port. see table 3. has a 2a internal pull-down current source.
ltc3576/ltc3576-1 14 3576fb dv cc (pin 12): logic supply for the i 2 c serial port. if the serial port is not needed, it can be disabled by grounding dv cc . when dv cc is grounded, the i 2 c bits are set to their default values. see table 3. scl (pin 13): clock input pin for the i 2 c serial port. the i 2 c logic levels are scaled with respect to dv cc . if dv cc is grounded, the scl pin is equivalent to the c2, c4 and c6 bits in the i 2 c serial port. scl in conjunction with sda determine the operating modes of switching regulators 1, 2 and 3 when dv cc is grounded. see tables 3 and 5. has a 2a internal pull-down current source. sda (pin 14): data input pin for the i 2 c serial port. the i 2 c logic levels are scaled with respect to dv cc . if dv cc is grounded, the sda pin is equivalent to the c3, c5 and c7 bits in the i 2 c serial port. sda in conjunction with scl determine the operating modes of switching regulators 1, 2 and 3 when dv cc is grounded. see tables 3 and 5. has a 2a internal pull-down current source. nc (pin 15): unconnected pin. this pin is not connected internally to the part. it is permissible to tie this pin to v in3 in order to make the v in3 pcb trace wider. v in3 (pin 16): power input for switching regulator 3. this pin will generally be connected to v out . a 1f mlcc capacitor is recommended on this pin. sw3 (pin 17): power transmission pin for switching regulator 3. nc (pin 18): unconnected pin. this pin is not connected internally to the part. it is permissible to tie this pin to sw3 in order to make the sw3 pcb trace wider. en3 (pin 19): logic input. this logic input pin indepen- dently enables switching regulator 3. active high. this pin is logically ored with its corresponding bit in the i 2 c serial port. see table 3. has a 2a internal pull-down current source. fb3 (pin 20): feedback input for switching regulator 3. when regulator 3s control loop is complete, this pin servos to 1 of 16 possible set points based on the commanded value from the i 2 c serial port. see table 4. rst3 (pin 21): logic output. this in an open-drain output which indicates that switching regulator 3 has settled to its ? nal value. it can be used as a power-on reset for the primary microprocessor or to enable the other switching regulators for supply sequencing. en2 (pin 22): logic input. this logic input pin indepen- dently enables switching regulator 2. active high. this pin is logically ored with its corresponding bit in the i 2 c serial port. see table 3. has a 2a internal pull-down current source. sw2 (pin 23): power transmission pin for switching regulator 2. v in2 (pin 24): power input for switching regulator 2. this pin will generally be connected to v out . a 1f mlcc capacitor is recommended on this pin. fb2 (pin 25): feedback input for switching regulator 2. when regulator 2s control loop is complete, this pin servos to 1 of 16 possible set points based on the commanded value from the i 2 c serial port. see table 4. v c (pin 26): bat-track external switching regulator control output. this pin drives the v c pin of an external linear technology step-down switching regulator. an external p-channel mosfet is sometimes required to provide power to v out with its gate tied to the acpr pin (see the applications information section). in concert with wall and acpr , it will regulate v out to maximize battery charger ef? ciency wall (pin 27): external power source sense input. wall should be connected to the output of the external high voltage switching regulator and to the drain of an external p-channel mosfet if used. it is used to determine when power is applied to the external regulator. when power is detected, acpr is driven low and the usb input is au- tomatically disabled. pulling this pin above 4.3v enables the v c pin. pin functions
ltc3576/ltc3576-1 15 3576fb acpr (pin 28): external power source present output (active low). acpr indicates that the output of the external high voltage step-down switching regulator is suitable for use by the ltc3576/ltc3576-1. it should be connected to the gate of an external p-channel mosfet whose source is connected to v out and whose drain is connected to wall. acpr has a high level of v out and a low level of gnd. the usb bidirectional switcher is disabled when acpr is low. prog (pin 29): charge current program and charge cur- rent monitor pin. connecting a 1% resistor from prog to ground programs the charge current. if suf? cient input power is available in constant-current mode, this pin servos to 1v. the voltage on this pin always represents the actual charge current by using the following formula: i bat = v prog r prog ? 1030 chrg (pin 30): open-drain charge status output. the chrg pin indicates the status of the battery charger. four possible charger states are represented by chrg : charging, not charging, unresponsive battery and battery temperature out of range. in addition, chrg is used to indicate whether there is a short-circuit condition on v bus when the bidirectional switching regulator is in step-up mode (on-the-go). chrg is modulated at 35khz and switches between a low and a high duty cycle for easy recognition by either humans or microprocessors. see table 1. chrg requires a pull-up resistor and/or led to provide indication. idgate (pin 31): ideal diode ampli? er output. this pin controls the gate of an optional external p-channel mosfet used as an ideal diode between v out and bat. the external ideal diode operates in parallel with the internal ideal diode. the source of the p-channel mosfet should be connected to v out and the drain should be connected to bat. if the external ideal diode mosfet is not used, idgate should be left ? oating. bat (pin 32): single cell li-ion battery pin. depending on available v bus power, a li-ion battery on bat will either deliver power to v out through the ideal diode or be charged from v out via the battery charger. v out (pin 33): output voltage of the bidirectional powerpath switching regulator in step-down mode and input voltage of the battery charger. the majority of the portable product should be powered from v out . the ltc3576/ltc3576-1 will partition the available power between the external load on v out and the internal bat- tery charger. priority is given to the external load and any extra power is used to charge the battery. an ideal diode from bat to v out ensures that v out is powered even if the load exceeds the allotted power from v bus or if the v bus power source is removed. in on-the-go mode, this pin delivers power to v bus via the sw pin. v out should be bypassed with a low impedance ceramic capacitor. v bus (pins 34, 35): power pins. these pins deliver power to v out via the sw pin by drawing controlled current from a dc source such as a usb port or dc output wall adapter. in on-the-go mode these pins provide power to external loads. tie the two v bus pins together at the part and bypass with a low impedance multilayer ceramic capacitor. sw (pin 36): the sw pin transfers power between v bus and v out via the bidirectional switching regulator. see the applications information section for a discussion of inductance value and current rating. i lim0 , i lim1 (pins 37, 38): i lim0 and i lim1 control the current limit of the powerpath switching regulator. see table 1. both the i lim0 and i lim1 pins are logically ored with their corresponding bits in the i 2 c serial port. see tables 3 and 6. each has a 2a internal pull-down current source. exposed pad (pin 39): ground. the exposed pad should be connected to a continuous ground plane on the second layer of the printed circuit board by several vias directly under the ltc3576/ltc3576-1. pin functions
ltc3576/ltc3576-1 16 3576fb block diagram 16 20 39 + + C + C enable v in3 sw3 fb3 gnd 3576 bd 37 i lim0 30 chrg 1 clprog 3 ntcbias 4 ntc 6 ovsens v c 5 ovgate 38 i lim1 11 enotg 10 en1 22 en2 19 en3 12 dv cc 14 sda 13 scl 1a 2.25mhz buck regulator 17 24 25 enable v in2 sw2 fb2 400ma 2.25mhz buck regulator 23 8 7 enable v in1 29 prog 32 bat 15mv 0.3v 3.6v ideal 1.18v or 1.15v + C 5.1v sw1 fb1 21 rst3 400ma 2.25mhz buck regulator 2.25mhz bidirectional powerpath switching regulator 9 d/a d/a d/a 4 4 4 i 2 c port i lim decode logic cc/cv charger 3.3v ldo charge status ovp 27 26 28 wall detect v c control 31 idgate 33 v out sw acpr wall + C + C + C battery temperature monitor suspend ldo 500a/2.5ma 36 ldo3v3 2 35 v bus 34 v bus
ltc3576/ltc3576-1 17 3576fb timing diagram t su,dat t hd,dat sda scl t hd,sta t su,sta t hd,sta t su,sto 3208 f05 t buf t low t high start condition repeated start condition stop condition start condition t r t f t sp i 2 c write protocol ack 123 write address r/ w 456789123456789123456789 00 010 01 0 00010010 a7 a6 a5 a4 a3 a2 a1 a0 b7 b6 b5 b4 b3 b2 b1 b0 ack stop start sda scl ack sub-address input data byte 3576 i2c
ltc3576/ltc3576-1 18 3576fb operation introduction the ltc3576/ltc3576-1 are highly integrated power man- agement ics designed to make optimal use of the power available from a variety of sources, while minimizing power dissipation and easing thermal budgeting constraints. they include a high ef? ciency bidirectional powerpath switching regulator, a controller for an external high volt- age step-down switching regulator, a battery charger, an ideal diode, an always-on ldo, an overvoltage protection circuit and three general purpose step-down switching regulators. the entire chip is controlled by either direct digital control or by an i 2 c serial port or both. the innovative powerpath architecture ensures that the application is powered immediately after external voltage is applied, even with a completely dead battery, by prioritizing power to the application. when acting as a step-down converter, the ltc3576/ ltc3576-1s bidirectional switching regulator takes power from usb, wall adapters, or other 5v sources and provides power to the application and ef? ciently charges the battery using bat-track. because power is conserved the ltc3576/ltc3576-1 allow the load current on v out to exceed the current drawn by the usb port making maxi- mum use of the allowable usb power for battery charging. for usb compatibility the switching regulator includes a precision average input current limit. the powerpath switching regulator and battery charger communicate to ensure that the average input current never exceeds the usb speci? cations. additionally, the bidirectional switching regulator can also operate as a 5v synchronous step-up converter taking power from v out and delivering up to 500ma to v bus without the need for any additional external components. this enables systems with usb dual-role transceivers to function as usb on-the-go dual-role devices. true output disconnect and average output current limit features are included for short-circuit protection. for automotive, ? rewire, and other high voltage applica- tions, the ltc3576/ltc3576-1 provide bat-track control of an external ltc step-down switching regulator to maximize battery charger ef? ciency and minimize heat production. when power is available from both the usb and an auxiliary input, the auxiliary input is given priority. the ltc3576/ltc3576-1 contain both an internal 180m ideal diode as well as an ideal diode controller for use with an optional external p-channel mosfet. the ideal diode(s) from bat to v out guarantee that ample power is always available to v out even if there is insuf? cient or absent power at v bus or wall. an always-on ldo provides a regulated 3.3v from avail- able power at v out . drawing very little quiescent current, this ldo will be on at all times and can be used to supply 20ma. the ltc3576/ltc3576-1 feature an overvoltage protection circuit which is designed to work with an external n-chan- nel mosfet to prevent damage to their inputs caused by accidental application of high voltage. to prevent battery drain when a device is connected to a suspended usb port, an ldo from v bus to v out provides either low power or high power usb suspend current to the application. the three general purpose switching regulators can be independently enabled either by direct digital control or by operating the i 2 c serial port. under i 2 c control, all three switching regulators have adjustable set points so that voltages can be reduced when high processor perfor- mance is not needed. along with constant frequency pwm mode, all three switching regulators have automatic burst mode operation and ldo modes for signi? cantly reduced quiescent current under light load conditions.
ltc3576/ltc3576-1 19 3576fb operation bidirectional powerpath switching regulator step-down mode the power delivered from v bus to v out is controlled by a 2.25mhz constant frequency bidirectional switching regulator operating in step-down mode. v out drives the combination of the external load (step-down switching regulators 1, 2 and 3) and the battery charger. to meet the maximum usb load speci? cation, the switching regulator contains a measurement and control system that ensures that the average input current remains below the level programmed at clprog. if the combined load does not cause the switching regu- lator to reach the programmed input current limit, v out will track approximately 0.3v above the battery voltage. by keeping the voltage across the battery charger at this low level, power lost to the battery charger is minimized. figure 1 shows the power ? ow in step-down mode. if the combined external load plus battery charge current is large enough to cause the switching regulator to reach the programmed input current limit, the battery charger will reduce its charge current by precisely the amount necessary to enable the external load to be satis? ed. even if the battery charge current is programmed to exceed the allowable usb current, the usb speci? cation for average input current will not be violated; the battery charger will reduce its current as needed. furthermore, if the load cur- rent at v out exceeds the programmed power from v bus , load current will be drawn from the battery via the ideal diode(s) even when the battery charger is enabled. the current out of clprog is a precise fraction of the v bus current. when a programming resistor and an averaging capacitor are connected from clprog to gnd, the volt- age on clprog represents the average input current of the switching regulator. as the input current approaches the programmed limit, clprog reaches 1.18v and power delivered by the switching regulator is held constant. + C + + C 0.3v 1.18v 3.6v clprog i switch /n + C + C 15mv omv ideal diode pwm and gate drive average v bus input current limit controller v bus voltage controller v out voltage controller constant current constant voltage battery charger + C 5v 1 idgate 31 v out 33 sw 3.5v to (bat + 0.3v) to system load optional external ideal diode pmos single cell li-ion 3576 f01 36 bat usb input battery power hv input 32 to usb or wall adapter 35 + 5 ovgate v bus 34 v bus 6 ovsens s 2 6v overvoltage protection to automotive, firewire, etc. acpr + C bat + 0.3v 3.6v v out 4.3v + + C + C 28 wall bat-track hv control 27 v c 26 sw fb v in v c high voltage step-down switching regulator + C + C figure 1. powerpath block diagrampower available from usb/wall adapter
ltc3576/ltc3576-1 20 3576fb operation the input current limit is programmed by the i lim0 and i lim1 pins or by the i 2 c serial port. the input current limit has ? ve possible settings ranging from the usb suspend limit of 500a up to 1a for wall adapter applications. two of these settings are speci? cally intended for use in the 100ma and 500ma usb applications. refer to table 1 for current limit settings using the i lim0 and i lim1 pins and table 6 for current limit settings using the i 2 c port. table 1. usb current limit settings using i lim0 and i lim1 i lim1 i lim0 usb setting 00 1 mode (usb 100ma limit) 01 10 mode (wall 1a limit) 1 0 low power suspend (usb 500a limit) 11 5 mode (usb 500ma limit) when the switching regulator is activated, the average input current will be limited by the clprog programming resistor according to the following expression: i vbus = i vbusq + v clprog r clprog ?h clprog + 1 () where i vbusq is the quiescent current of the ltc3576/ ltc3576-1, v clprog is the clprog servo voltage in current limit, r clprog is the value of the programming resistor and h clprog is the ratio of the measured cur- rent at v bus to the sample current delivered to clprog. refer to the electrical characteristics table for values of h clprog , v clprog and i vbusq . given worst-case circuit tolerances, the usb speci? cation for the average input current in 100ma or 500ma mode will not be violated, provided that r clprog is 3.01k or greater. while not in current limit, the switching regulators bat-track feature will set v out to approximately 300mv above the voltage at bat. however, if the voltage at bat is below 3.3v, and the load requirement does not cause the switching regulator to exceed its current limit, v out will regulate at a ? xed 3.6v as shown in figure 2. this instant-on operation will allow a portable product to run immediately when power is applied without waiting for the battery to charge. if the load does exceed the current limit at v bus , v out will range between the no-load voltage and slightly below the battery voltage, indicated by the shaded region of figure 2. bat (v) 2.4 4.5 4.2 3.9 3.6 3.3 3.0 2.7 2.4 3.3 3.9 3576 f02 2.7 3.0 3.6 4.2 v out (v) no load 300mv figure 2. v out vs bat for very low-battery voltages, the battery charger acts like a load and, due to limited input power, its current will tend to pull v out below the 3.6v instant-on voltage. to prevent v out from falling below this level, an undervoltage circuit automatically detects that v out is falling and reduces the battery charge current as needed. this reduction ensures that load current and voltage are always prioritized while allowing as much battery charge current as possible. see battery charger over programming in the applications information section. the voltage regulation loop is compensated by the ca- pacitance on v out . a 10f mlcc capacitor is required for loop stability. additional capacitance beyond this value will improve transient response. an internal undervoltage lockout circuit monitors v bus and keeps the switching regulator off until v bus rises above 4.30v and is about 200mv above the battery voltage. hysteresis on the uvlo turns off the regulator if v bus falls below 4v or to within 50mv of the battery voltage. when this happens, system power at v out will be drawn from the battery via the ideal diode(s). bidirectional powerpath switching regulator step-up mode for usb on-the-go applications, the bidirectional powerpath switching regulator acts as a step-up converter to deliver power from v out to v bus . the power from v out can come from the battery or the output of the external
ltc3576/ltc3576-1 21 3576fb operation high voltage switching regulator. as a step-up converter, the bidirectional switching regulator produces 5v on v bus and is capable of delivering at least 500ma. usb on-the-go can be enabled by either the external control pin, enotg, or via i 2 c. figure 3 shows the power ? ow in step-up mode. an undervoltage lockout circuit monitors v out and pre- vents step-up conversion until v out rises above 2.8v. to prevent backdriving of v bus when input power is available, the v bus undervoltage lockout circuit prevents step-up conversion if v bus is greater than 4.3v at the time step-up mode is enabled. the switching regulator is also designed to allow true output disconnect by eliminating body diode conduction of the internal pmos switch. this allows v bus to go to zero volts during a short-circuit condition or while shut down, drawing zero current from v out . the voltage regulation loop is compensated by the capaci- tance on v bus . a 4.7f mlcc is required for loop stability. additional capacitance beyond this value will improve transient response. the v bus voltage has approximately 3% load regulation up to an output current of 500ma. at light loads, the switching regulator goes into burst mode operation. the regulator will deliver power to v bus until it reaches 5.1v after which the nmos and pmos switches shut off. the regulator delivers power again to v bus once it falls below 5.1v. the switching regulator features both peak inductor and average output current limit. the peak current mode architecture limits peak inductor current on a cycle-by- cycle basis. the peak current limit is equal to v bus /2 to a maximum of 1.8a so that in the event of a sudden short circuit, the current limit will fold back to a lower value. in step-up mode, the voltage on clprog represents the average output current of the switching regulator when a programming resistor and an averaging capacitor are connected from clprog to gnd. with a 3.01k resistor on clprog, the bidirectional switching regulator has an output current limit of 680ma. as the output current ap- + C + + C 0.3v 1.15v 3.6v clprog i switch /n + C + C 15mv omv ideal diode pwm and gate drive average v bus output current limit controller v bus voltage controller v out voltage controller constant current constant voltage battery charger + C 5v 1 idgate 31 v out 33 sw 3.5v to (bat + 0.3v) to system load optional external ideal diode pmos single cell li-ion 3576 f03 36 bat 32 to usb cable 35 + 5 ovgate v bus 34 v bus 6 ovsens to automotive, firewire, etc. acpr bat + 0.3v 3.6v v out 4.3v + + C + C 28 wall bat-track hv control 27 v c 6v 26 sw fb v in v c high voltage step-down switching regulator + C s 2 overvoltage protection + C + C battery power hv input figure 3. powerpath block diagramusb on-the-go
ltc3576/ltc3576-1 22 3576fb operation proaches this limit clprog servos to 1.15v and v bus falls rapidly to v out . when v bus is close to v out there may not be suf? cient negative slope on the inductor current when the pmos switch is on to balance the rise in the inductor current when the nmos switch is on. this will cause the inductor current to run away and the voltage on clprog to rise. when clprog reaches 1.2v the switching of the synchronous pmos is terminated and v out is applied statically to its gate. this ensures that the inductor current will have suf? cient negative slope during the time current is ? owing to the output. the pmos will resume switching when clprog drops down to 1.15v. the ltc3576/ltc3576-1 maintain voltage regulation even if v out is above v bus . this is achieved by disabling the pmos switch. the pmos switch is enabled when v bus rises above v out + 180mv and is disabled when it falls below v out + 70mv to prevent the inductor current from running away when not in current limit. since the pmos no longer acts as a low impedance switch in this mode, there will be more power dissipation within the ic. this will cause a sharp drop in ef? ciency. if v bus is less than 4v and the pmos switch is disabled for more than 7.2ms a short-circuit fault will be declared and the part will shut off. the chrg pin will blink at 35khz with a duty cycle that varies between 12% and 88% at a 4hz rate. see table 2. to re-enable step-up mode, the enotg pin or, with enotg grounded, the b0 bit in the i 2 c port must be cycled low and then high. bat-track auxiliary high voltage switching regulator control the wall, acpr and v c pins can be used in conjunction with an external high voltage step-down switching regula- tor such as the lt ? 3480 or the lt3653 to minimize heat production when operating from higher voltage sources, as shown in figures 1 and 3. bat-track control circuitry regulates the external switching regulators output voltage to the larger of (bat + 300mv) or 3.6v. this maximizes battery charger ef? ciency while still allowing instant-on operation when the battery is deeply discharged. the feedback network of the high voltage regulator should be set to generate an output voltage between 4.5v and 5.5v. when high voltage is applied to the external regulator, wall will rise toward this programmed output voltage. when wall exceeds approximately 4.3v, acpr is brought low and the bat-track control of the ltc3576/ltc3576-1 overdrives the local v c control of the external high volt- age step-down switching regulator. therefore, once the bat-track control is enabled, the output voltage is set in- dependent of the switching regulator feedback network. bat-track control provides a signi? cant ef? ciency advantage over the simple use of a 5v switching regulator output to drive the battery charger. with a 5v output driving v out , battery charger ef? ciency is approximately: total = buck ? v bat 5v where buck is the ef? ciency of the high voltage switching regulator and 5v is the output voltage of the switching regulator. with a typical switching regulator ef? ciency of 87% and a typical battery voltage of 3.8v, the total bat- tery charger ef? ciency is approximately 66%. assuming a 1a charge current, 1.7w of power is dissipated just to charge the battery! with bat-track, battery charger ef? ciency is approxi- mately: total = buck ? v bat v bat + 0.3v with the same assumptions as above, the total battery charger ef? ciency is approximately 81%. this example works out to less than 1w of power dissipation, or almost 60% less heat. see the typical applications section for complete circuits using the lt3480 and the lt3653 with bat-track control. ideal diode(s) from bat to v out the ltc3576/ltc3576-1 each have an internal ideal diode as well as a controller for an optional external ideal diode. both the internal and the external ideal diodes are always on and will respond quickly whenever v out drops below bat. if the load current increases beyond the power allowed from the switching regulator, additional power will be pulled from the battery via the ideal diode(s). further- more, if power to v bus (usb or wall adapter) is removed,
ltc3576/ltc3576-1 23 3576fb operation then all of the application power will be provided by the battery via the ideal diodes. the ideal diode(s) will be fast enough to keep v out from drooping with only the stor- age capacitance required for the switching regulator. the internal ideal diode consists of a precision ampli? er that activates a large on-chip p-channel mosfet whenever the voltage at v out is approximately 15mv (v fwd ) below the voltage at bat. within the ampli? ers linear range, the small-signal resistance of the ideal diode will be quite low, keeping the forward drop near 15mv. at higher current levels, the mosfet will be in full conduction. to supplement the internal ideal diode, an external p-channel mosfet may be added from bat to v out . the idgate pin of the ltc3576/ltc3576-1 drives the gate of the external p-channel mosfet for automatic ideal diode control. the source of the external p-channel mosfet should be connected to v out and the drain should be con- nected to bat. capable of driving a 1nf load, the idgate pin can control an external p-channel mosfet transistor having an on-resistance of 30m or lower. suspend ldo if the ltc3576/ltc3576-1 are con? gured for usb suspend mode, the bidirectional switching regulator is disabled and the suspend ldo provides power to the v out pin (presum- ing there is power available to v bus ). this ldo will prevent the battery from running down when the portable product has access to a suspended usb port. regulating at 4.6v, this ldo only becomes active when the switching converter is disabled (suspended). the suspend ldo sends a scaled copy of the v bus current to the clprog pin, which will servo to approximately 100mv in this mode. to remain compliant with the usb speci? cation, the input to the ldo is current limited so that it will not exceed the low power or high power suspend speci? cation. if the load on v out exceeds the suspend current limit, the additional current will come from the battery via the ideal diode(s). 3.3v always-on ldo supply the ltc3576/ltc3576-1 include a low quiescent current low dropout regulator that is always powered. this ldo can be used to provide power to a system pushbutton controller, standby microcontroller or real time clock. de- signed to deliver up to 20ma, the always-on ldo requires at least a 1f low impedance ceramic bypass capacitor for compensation. the ldo is powered from v out , and therefore will enter dropout at loads less than 20ma as v out falls near 3.3v. if the ldo3v3 output is not used, it should be disabled by connecting it to v out . battery charger the ltc3576/ltc3576-1 include a constant-current/con- stant-voltage battery charger with automatic recharge, automatic termination by safety timer, low voltage trickle charging, bad cell detection and thermistor sensor input for out-of-temperature charge pausing. battery preconditioning when a battery charge cycle begins, the battery charger ? rst determines if the battery is deeply discharged. if the battery voltage is below v trkl , typically 2.85v, an automatic trickle charge feature sets the battery charge current to 10% of the programmed value. if the low voltage persists for more than 1/2 hour, the battery charger automatically terminates and indicates via the chrg pin that the battery was unresponsive. once the battery voltage is above 2.85v, the charger begins charging in full power constant-current mode. the cur- rent delivered to the battery will try to reach 1030/r prog . depending on available input power and external load conditions, the battery charger may or may not be able to charge at the full programmed rate. the external load will always be prioritized over the battery charge current. forward voltage (mv) (bat C v out ) 0 current (ma) 600 1800 2000 2200 120 240 300 3576 f04 200 1400 1000 400 1600 0 1200 800 60 180 360 480 420 vishay si2333 optional external ideal diode ltc3576/ ltc3576-1 ideal diode on semiconductor mbrm120lt3 figure 4. ideal diode v-i characteristics
ltc3576/ltc3576-1 24 3576fb operation likewise, the usb current limit programming will always be observed and only additional power will be available to charge the battery. when system loads are light, battery charge current will be maximized. charge termination the battery charger has a built-in safety timer. when the voltage on the battery reaches the pre-programmed ? oat voltage, the battery charger will regulate the battery volt- age and the charge current will decrease naturally. once the battery charger detects that the battery has reached the ? oat voltage, the four hour safety timer is started. after the safety timer expires, charging of the battery will discontinue and no more current will be delivered. automatic recharge after the battery charger terminates, it will remain off drawing only microamperes of current from the battery. if the portable product remains in this state long enough, the battery will eventually self discharge. to ensure that the battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below the recharge threshold which is typically 100mv less than the chargers ? oat voltage. in the event that the safety timer is running when the battery voltage falls below the recharge threshold, it will reset back to zero. to prevent brief excursions below the recharge threshold from resetting the safety timer, the battery voltage must be below the recharge threshold for more than 1ms. the charge cycle and safety timer will also restart if the v bus uvlo cycles low and then high (e.g., v bus is removed and then replaced), or if the battery charger is cycled on and off by the i 2 c port. charge current the charge current is programmed using a single resis- tor from prog to ground. 1/1030th of the battery charge current is sent to prog which will attempt to servo to 1.000v. thus, the battery charge current will try to reach 1030 times the current in the prog pin. the program resistor and the charge current are calculated using the following equation: i chg = v prog r prog ? 1030 in either the constant-current or constant-voltage charging modes, the voltage at the prog pin will be proportional to the actual charge current delivered to the battery. there- fore, the actual charge current can be determined at any time by monitoring the prog pin voltage and using the following equation: i bat = v prog r prog ?1030 in many cases, the actual battery charge current, i bat , will be lower than i chg due to limited input power available and prioritization with the system load drawn from v out . the battery charger flow chart illustrates the battery chargers algorithm. charge status indication the chrg pin indicates the status of the battery charger. four possible states are represented by chrg which include charging, not charging, unresponsive battery and battery temperature out of range. the signal at the chrg pin can be easily recognized as one of the above four states by either a human or a mi- croprocessor. an open-drain output, the chrg pin can drive an indicator led through a current limiting resistor for human interfacing or simply a pull-up resistor for microprocessor interfacing. to make the chrg pin easily recognized by both humans and microprocessors, the pin is either low for charging, high for not charging, or it is switched at high frequency (35khz) to indicate the two possible faults, unresponsive battery and battery temperature out of range. when charging begins, chrg is pulled low and remains low for the duration of a normal charge cycle. when charging is complete, i.e., the bat pin reaches the ? oat voltage and the charge current has dropped to one-tenth of the programmed value, the chrg pin is released (hi-z). if a fault occurs, the pin is switched at 35khz. while switching, its duty cycle is modulated between a high and low value at a very low frequency. the low and high duty cycles are disparate enough to make an led appear to be on or off thus giving the appearance of blinking.
ltc3576/ltc3576-1 25 3576fb operation battery charger flow chart clear event timer ntc out of range chrg currently high-z indicate ntc fault at chrg battery state charge at 1030v/r prog rate pause event timer pause event timer charge with fixed voltage (v float ) run event timer charge at 100v/r prog (c/10 rate) run event timer assert chrg low power on/ enable charger timer > 30 minutes timer > 4 hours bat > 2.85v bat < v rechrg i bat < c/10 no no yes yes yes yes yes yes no no bat > v float C e bat < 2.85v 2.85v < bat < v float C e no no no no inhibit charging stop charging indicate battery fault at chrg bat rising through v rechrg bat falling through v rechrg chrg high-z chrg high-z 3576 flow no yes yes inhibit charging yes
ltc3576/ltc3576-1 26 3576fb operation each of the two faults has its own unique blink rate for human recognition as well as two unique duty cycles for machine recognition. the chrg pin does not respond to the c/10 threshold if the ltc3576/ltc3576-1 is in v bus current limit. this prevents false end of charge indications due to insuf? cient power available to the battery charger. table 2 illustrates the four possible states of the chrg pin when the battery charger is active. table 2. chrg signal status frequency modulation (blink) frequency duty cycles charging 0hz 0hz (low-z) 100% not charging 0hz 0hz (hi-z) 0% ntc fault 35khz 1hz at 50% 6%, 94% bad battery or on-the-go short-circuit fault 35khz 4hz at 50% 12%, 88% an ntc fault is represented by a 35khz pulse train whose duty cycle alternates between 6% and 94% at a 1hz rate. a human will easily recognize the 1hz rate as a slow blink- ing which indicates the out-of-range battery temperature while a microprocessor will be able to decode either the 6% or 94% duty cycles as an ntc fault. if a battery is found to be unresponsive to charging (i.e., its voltage remains below 2.85v for 1/2 hour), the chrg pin gives the bad battery fault indication. for this fault, a human would easily recognize the 4hz fast blink of the led while a microprocessor would be able to decode either the 12% or 88% duty cycles as a bad battery fault. note that the ltc3576/ltc3576-1 are 3-terminal powerpath products where system load is always priori- tized over battery charging. due to excessive system load, there may not be suf? cient power to charge the battery beyond the trickle charge threshold voltage within the bad battery timeout period. in this case, the battery charger will falsely indicate a bad battery. system software may then reduce the load and reset the battery charger to try again. in addition to charge status, the chrg pin is also used to indicate whether there is a short-circuit condition on v bus when the bidirectional switching regulator is in on- the-go mode. when a short-circuit condition is detected, chrg will blink with the same modulation frequency and duty cycle as a bad battery fault. if the charger is on at the same time that on-the-go is enabled, a 4hz modulation of 12% and 88% duty cycles on chrg could indicate a bad battery or a short-circuit fault on v bus . system software should turn off the charger or on-the-go to determine which fault has occurred. although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). when this happens the duty cycle reading will be precisely 50%. if the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading. ntc thermistor the battery temperature is measured by placing a nega- tive temperature coef? cient (ntc) thermistor close to the battery pack. to use this feature connect the ntc thermistor, r ntc , be- tween the ntc pin and ground and a bias resistor, r nom , from ntcbias to ntc. r nom should be a 1% 200ppm resistor with a value equal to the value of the chosen ntc thermistor at 25c (r25). the ltc3576/ltc3576-1 pauses charging when the re- sistance of the ntc thermistor drops to 0.54 times the value of r25 or approximately 54k for a 100k thermistor. for a vishay curve 1 thermistor, this corresponds to ap- proximately 40c. if the battery charger is in constant voltage (? oat) mode, the safety timer also pauses until the thermistor indicates a return to a valid temperature. as the temperature drops, the resistance of the ntc thermistor rises. the ltc3576/ltc3576-1 are also designed to pause charging when the value of the ntc thermistor increases to 3.25 times the value of r25. for a vishay curve 1 100k thermistor, this resistance, 325k, corresponds to approximately 0c. the hot and cold comparators each have approximately 3c of hysteresis to prevent oscilla- tion about the trip point. grounding the ntc pin disables all ntc functionality.
ltc3576/ltc3576-1 27 3576fb operation thermal regulation to prevent thermal damage to the ltc3576/ltc3576-1 or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to 105c. this thermal regulation technique protects the ltc3576/ltc3576-1 from excessive temperature due to high power operation or high ambient thermal conditions, and allows the user to push the limits of the power handling capability with a given circuit board design. the bene? t of the ltc3576/ ltc3576-1 thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions for a given application with the assurance that the charger will automatically reduce the current in worst-case conditions. overvoltage protection the ltc3576/ltc3576-1 can protect itself from the inadver- tent application of excessive voltage to v bus or wall with just two external components: an n-channel mosfet and a 6.2k resistor. the maximum safe overvoltage magnitude will be determined by the choice of the external mosfet and its associated drain breakdown voltage. the overvoltage protection module consists of two pins. the ? rst, ovsens, is used to measure the externally ap- plied voltage through an external resistor. the second, ovgate, is an output used to drive the gate pin of the external mosfet. when ovsens is below 6v, an internal charge pump will drive ovgate to approximately 1.88 ovsens. this will enhance the n-channel mosfet and provide a low impedance connection to v bus or wall which will, in turn, power the ltc 3576/ltc3576-1 . if ovsens should rise above 6v due to a fault or use of an incorrect wall adapter, ovgate will be pulled to gnd disabling the external mosfet and therefore protecting downstream circuitry. when the voltage drops below 6v again, the external mosfet will be re-enabled. when usb on-the-go is enabled, the bidirectional switch- ing regulator powers up the overvoltage protection circuit through the body diode of the external mosfet, thus pro- viding protection to the part even when v bus is sourcing power. when high voltage is applied to the drain of the external mosfet, v bus will remain at 5v. once the high voltage is removed, the drain of the external mosfet will return to 5v. the charge pump output on ovgate has limited output drive capability. care must be taken to avoid leakage on this pin as it may adversely affect operation. see the applications information section for resistor power dissipation rating calculations, a table of recommended components, and examples of dual-input and reverse input protection. i 2 c interface the ltc3576/ltc3576-1 may receive commands from a host (master) using the standard 2-wire i 2 c interface. the timing diagram shows the timing relationship of the sig- nals on the bus. the two bus lines, sda and scl, must be high when the bus is not in use. external pull-up resistors or current sources, such as the ltc1694 i 2 c accelerator, are required on these lines. the ltc3576/ltc3576-1are receive-only slave devices. the i 2 c control signals, sda and scl are scaled internally to the dv cc supply. dv cc should be connected to the same power supply as the microcontroller generating the i 2 c signals. the i 2 c port has an undervoltage lockout on the dv cc pin. when dv cc is below approximately 1v, the i 2 c serial port is cleared and switching regulators 1, 2 and 3 are set to full scale. bus speed the i 2 c port is designed to be operated at speeds of up to 400khz. it has built-in timing delays to ensure correct operation when addressed from an i 2 c compliant master device. it also contains input ? lters designed to suppress glitches should the bus become corrupted. start and stop conditions a bus master signals the beginning of a communication to a slave device by transmitting a start condition. a start condition is generated by transitioning sda from high to low while scl is high. when the master has ? nished communicating with the slave, it issues a stop condition by transitioning sda from low to high while scl is high. the bus is then free for communication with another i 2 c device.
ltc3576/ltc3576-1 28 3576fb operation byte format each byte sent to the ltc3576/ltc3576-1 must be eight bits long followed by an extra clock cycle for the acknowledge bit. the data should be sent to the ltc3576/ltc3576-1 with the most signi? cant bit (msb) ? rst. acknowledge the acknowledge signal is used for handshaking between the master and the slave. an acknowledge (active low) generated by the slave (ltc3576/ltc3576-1) lets the mas- ter know that the latest byte of information was received. the acknowledge related clock pulse is generated by the master. the master releases the sda line (high) during the acknowledge clock cycle. the slave-receiver must pull down the sda line during the acknowledge clock pulse so that it remains a stable low during the high period of this clock pulse. slave address the address byte consists of the 7-bit address and the read/ write (r/ w ) bit. the ltc3576/ltc3576-1 respond to only one 7-bit address which has been factory programmed to 0001001. the r/ w bit is the least signi? cant bit of the address byte. it must be 0 for the ltc3576/ltc3576-1 to recognize the address since they are write only devices. thus the address byte is 0x12. if the correct seven bit ad- dress is given but the r/ w bit is 1, the ltc3576/ltc3576-1 will not respond. sub-addressed writing the ltc3576/ltc3576-1 have four command registers for control input. they are accessed by the i 2 c port via a sub-addressed writing system. each write to the ltc3576/ltc3576-1 consists of three bytes. the ? rst byte is always the ltc3576/ltc3576-1s write address. the second byte represents the ltc3576/ ltc3576-1s sub-address. the sub-address acts as pointer to direct the subsequent data byte within the ltc3576/ltc3576-1. the third byte consists of the data to be written to the location pointed to by the sub-address. the ltc 3576/ltc3576-1 contain four sub-addresses at locations 0x00, 0x01, 0x02 and 0x03. bus write operation the master initiates communication with the ltc3576/ ltc3576-1 with a start condition and a 7-bit address followed by the r/ w bit = 0. if the address matches that of the ltc3576/ltc3576-1, the ltc3576/ltc3576-1 return an acknowledge. the master should then deliver the sub- address. again the ltc3576/ltc3576-1 acknowledge and the cycle is repeated for the data byte. the data byte is transferred to an internal holding latch upon the return of its acknowledge by the ltc3576/ltc3576-1. this procedure must be repeated for each sub-address that requires new data. after one or more data bytes have been transferred to the ltc3576/ltc3576-1, the master may terminate the communication with a stop condition. alternatively, a repeated start condition can be initiated by the master and another chip on the i 2 c bus can be addressed. this cycle can continue inde? nitely and the ltc3576/ltc3576-1 remembers the last input of valid data that it received. once all chips on the bus have been addressed and sent valid data, a global stop condition can be sent and the ltc3576/ltc3576-1 will update their command latches with the data that they have received. in certain circumstances the data on the i 2 c bus may be- come corrupted. in these cases, the ltc3576/ltc3576-1 respond appropriately by preserving only the last set of complete data that they have received. for example, assume the ltc3576/ltc3576-1 have been successfully addressed and are receiving data when a stop condition mistakenly occurs. the ltc3576/ltc3576-1 will ignore this stop condition and will not respond until a new start condition, correct address and sub-address, new set of data and stop condition are transmitted. likewise, with only one exception, if the ltc3576/ ltc3576-1 were previously addressed and sent valid data but not updated with a stop , they will respond to any stop that appears on the bus, independent of the num- ber of repeated starts that have occurred. if a repeated start is given and the ltc3576/ltc3576-1 successfully acknowledge their address and sub-address, they will not respond to a stop until a full byte of the new data has been received and acknowledged.
ltc3576/ltc3576-1 29 3576fb operation input data table 3 illustrates the four data bytes that may be written to the ltc3576/ltc3576-1. the ? rst byte at sub-address 0 controls the servo volt- age for switching regulators 1 and 2. the second byte at sub-address 1 controls the servo voltage of switching regulator 3 and the enable signals for all three switching regulators, as well as the enable signal for the powerpath switching regulator to power up v bus for usb on-the-go. the servo voltages are decoded in table 4. the default servo voltage is 0.8v. table 3. i 2 c serial port mapping* a7 a6 a5 a4 a3 a2 a1 a0 b7 b6 b5 b4 b3 b2 b1 b0 switching regulator 1 voltage (see table 4) switching regulator 2 voltage (see table 4) switching regulator 3 voltage (see table 4) enable 3 enable 2 enable 1 enable otg reset value 1 1 1 1111111110000 c7 c6 c5 c4 c3 c2 c1 c0 d7 d6 d5 d4 d3 d2 d1 d0 switching regulator 1 modes (see table 5) switching regulator 2 modes (see table 5) switching regulator 3 modes (see table 5) input current limit (see table 6) disable battery charger high power suspend unused reset value 0 0 0 0000000000000 *the a7-a0 and b7-b4 bits default to 1 and all other bits default to 0 when the chip is powered and dv cc = 0. table 4. switching regulator servo voltage a7 a6 a5 a4 switching regulator 1 servo voltage a3 a2 a1 a0 switching regulator 2 servo voltage b7 b6 b5 b4 switching regulator 3 servo voltage 0 0 0 0 0.425 0 0 0 1 0.450 0 0 1 0 0.475 0 0 1 1 0.500 0 1 0 0 0.525 0 1 0 1 0.550 0 1 1 0 0.575 0 1 1 1 0.600 1 0 0 0 0.625 1 0 0 1 0.650 1 0 1 0 0.675 1 0 1 1 0.700 1 1 0 0 0.725 1 1 0 1 0.750 1 1 1 0 0.775 1 1 1 1 0.800
ltc3576/ltc3576-1 30 3576fb operation the third data byte at sub-address 2 controls the operating modes of each switching regulator as well as the input current limit settings. each switching regulator can be independently set to one of three operating modes listed in table 5. table 5. general purpose switching regulator modes c7 (sda)* c6 (scl)* switching regulator 1 mode c5 (sda)* c4 (scl)* switching regulator 2 mode c3 (sda)* c2 (scl)* switching regulator 3 mode 0 x pulse-skipping mode 1 0 ldo mode 1 1 burst mode operation *sda and scl take on this context only when dv cc = 0v. the input current limit settings are decoded according to table 6. this table indicates the maximum current that will be drawn from the v bus pin in the event that the load at v out (battery charger plus system load) exceeds the power available. any additional power will be drawn from the battery. the start-up state for the input current limit setting is 00 representing the low power 100ma usb setting. table 6. usb current limit settings d6 c1 (i lim1 )* c0 (i lim0 )* usb setting x0 0 1 mode (usb 100ma limit) x0 1 10 mode (wall 1a limit) 0 1 0 low power suspend (usb 500a limit) 1 1 0 high power suspend (usb 2.5ma limit) x1 1 5 mode (usb 500ma limit) *i lim1 and i lim0 can only be used to enable the low power suspend mode and are logically ored with c1 and c0, respectively. the fourth and ? nal byte of input data at sub-address 3 provides bits for disabling the battery charger and enabling the high power suspend mode current limit of 2.5ma. disabling the i 2 c port the i 2 c serial port can be disabled by grounding the dv cc pin. in this mode, the ltc3576/ltc3576-1 are controlled through the individual logic input pins en1, en2, en3, enotg, i lim0 , i lim1 , sda and scl. some functionality is not available in this mode such as the programmability of switching regulators 1, 2 and 3s output voltage, the battery charger disable feature and the high power suspend mode. in this mode, the programmable switching regulators have a ? xed servo voltage of 0.8v. because the sda and scl pins have no other context when dv cc is grounded, these pins are re-mapped to control the switching regulator mode bits c2 to c7. scl maps to c2, c4 and c6 while sda maps to c3, c5 and c7. rst3 pin the rst3 pin is an open-drain output used to indicate that switching regulator 3 has been enabled and has reached its ? nal voltage. rst3 remains low impedance until regula- tor 3 reaches 92% of its regulation value. a 230ms delay is included to allow a system microcontroller ample time to reset itself. rst3 may be used as a power- on reset to the microprocessor powered by regulator 3 or may be used to enable regulators 1 and/or 2 for supply sequencing. rst3 is an open-drain output and requires a pull-up resistor to the output voltage of regulator 3 or another appropriate power source. shutdown mode the bidirectional usb switching regulator in step-down mode is enabled whenever v bus is above v uvlo and the ltc3576/ltc3576-1are not in one of the two usb suspend modes (500a or 2.5ma). when power is available from both the usb and auxiliary inputs, the auxiliary input is given priority and the usb switching regulator is disabled. the ideal diode(s) are enabled at all times and cannot be disabled.
ltc3576/ltc3576-1 31 3576fb operation step-down switching regulators the ltc3576/ltc3576-1 contain three general purpose 2.25mhz step-down constant-frequency current mode switching regulators. two regulators provide up to 400ma and a third switching regulator can provide up to 1a. all three switching regulators can be programmed for a minimum start-up output voltage of 0.8v and can be used to power a microcontroller core, microcontroller i/o, memory, disk drive or other logic circuitry. all three switching regulators have i 2 c programmable set points for on-the-? y power savings. they also support 100% duty cycle operation (low dropout mode) when their input volt- age drops very close to their output voltage. to suit a variety of applications, selectable mode functions can be used to trade off noise for ef? ciency. three modes are available to control the operation of the ltc3576/ltc3576-1s general purpose switching regulators. at moderate to heavy loads, the pulse skip mode provides the lowest noise switching solution. at lighter loads, burst mode operation or ldo mode may be selected. the switching regulators include soft-start to limit inrush current when powering on, short- circuit current protection and switch node slew limiting circuitry to reduce radiated emi. no external compensa- tion components are required. the operating mode of the regulators may be set by either i 2 c control or by manual control of the sda and scl pins if the i 2 c port is not used. each converter may be individually enabled by either their external control pins en1, en2, en3 or by the i 2 c port. all three switching regulators have individual programmable feedback servo voltages via i 2 c control. the switching regulator input supplies v in1 , v in2 and v in3 will generally be connected to the system load pin v out . step-down switching regulator operating modes the ltc3576/ltc3576-1s general purpose switching regulators include three possible operating modes to meet the noise/power needs of a variety of applications. in pulse-skipping mode, an internal latch is set at the start of every cycle which turns on the main p-channel mosfet switch. during each cycle, a current comparator compares the peak inductor current to the output of an error ampli? er. the output of the current comparator resets the internal latch which causes the main p-channel mosfet switch to turn off and the n-channel mosfet synchronous recti? er to turn on. the n-channel mosfet synchronous recti? er turns off at the end of the 2.25mhz cycle or if the current through the n-channel mosfet synchronous recti? er drops to zero. using this method of operation, the error ampli? er adjusts the peak inductor current to deliver the required output power. all necessary compensation is internal to the switching regulator requiring only a single ceramic output capacitor for stability. at light loads in pwm mode, the inductor current may reach zero on each pulse which will turn off the n-channel mosfet synchronous recti? er. in this case, the switch node (sw) goes high impedance and the switch node voltage will ring. this is discontinuous mode operation, and is normal behavior for a switching regulator. at very light loads in pulse-skip- ping mode, the switching regulators will automatically skip pulses as needed to maintain output regulation. at high duty cycles (v outx > v inx /2) it is possible for the inductor current to reverse, causing the regulator to operate continuously at light loads. this is normal and regulation is maintained, but the supply current will increase to several ma due to continuous switching.
ltc3576/ltc3576-1 32 3576fb operation in burst mode operation, the switching regulator automati- cally switches between ? xed frequency pwm operation and hysteretic control as a function of the load current. at light loads, the regulator operates in hysteretic mode and uses a constant current algorithm to control the inductor cur- rent. while in burst mode operation, the output capacitor is charged to a voltage slightly higher than the regulation point. the step-down switching regulator then goes into sleep mode, during which the output capacitor provides the load current. in sleep mode, most of the regulators circuitry is powered down, conserving battery power. when the output voltage drops below a pre-determined value, the switching regulator circuitry is powered on and another burst cycle begins. the duration for which the regulator operates in sleep mode depends on the load current. the sleep time decreases as the load current increases. burst mode operation provides a signi? cant improvement in ef? ciency at light loads at the expense of higher output ripple when compared to pulse-skipping mode. at heavy loads burst mode operation functions in the same manner as pulse-skipping mode. finally, the switching regulators have an ldo mode that gives a dc option for regulating their output voltages. in ldo mode, the switching regulators are converted to linear regulators and deliver continuous power from their swx pins through their respective inductors. this mode gives the lowest possible output noise as well as low quiescent current at light loads. the step-down switching regulators allow on-the-? y mode transitions, providing seamless transition between modes even under load. this allows the user to switch back and forth between modes to reduce output ripple or increase low current ef? ciency as needed. step-down switching regulator dropout operation it is possible for a switching regulators input voltage, v inx , to approach its programmed output voltage (e.g., a battery voltage of 3.4v with a programmed output voltage of 3.3v). when this happens, the pmos switch duty cycle increases until it is turned on continuously at 100%. in this dropout condition, the respective output voltage equals the regulators input voltage minus the voltage drops across the internal p-channel mosfet and the inductor. step-down switching regulator low supply operation the ltc3576/ltc3576-1 incorporate an undervoltage lockout circuit on v out which shuts down the general purpose switching regulators when v out drops below v out(uvlo) . this uvlo prevents unstable operation. step-down switching regulator soft-start operation soft-start is accomplished by gradually increasing the peak inductor current for each switching regulator over a 500s period. this allows each output to rise slowly, help- ing minimize the battery surge current. a soft-start cycle occurs whenever a given switching regulator is enabled, or after a fault condition has occurred (thermal shutdown or uvlo). a soft-start cycle is not triggered by changing operating modes. this allows seamless output operation when transitioning between burst mode operation, pulse- skipping mode or ldo mode. step-down switching regulator switching slew rate control the step-down switching regulators contain new patent pending circuitry to limit the slew rate of the switch node (swx). this new circuitry is designed to transition the switch node over a period of a couple of nanoseconds, signi? cantly reducing radiated emi and conducted supply noise. step-down switching regulator in shutdown the step-down switching regulators are in shutdown when not enabled for operation. in shutdown, all circuitry in the step-down switching regulator is disconnected from the switching regulator input supply leaving only a few nanoamperes of leakage current. the step-down switching regulator outputs are individually pulled to ground through a 10k resistor on their swx pins when in shutdown.
ltc3576/ltc3576-1 33 3576fb applications information bidirectional powerpath switching regulator clprog resistor and capacitor selection as described in the bidirectional switching regula- torstep-down mode section, the resistor on the clprog pin determines the average v bus input current limit when the switching regulator is set to either the 1 mode (usb 100ma), the 5 mode (usb 500ma) or the 10 mode. the v bus input current will be comprised of two components, the current that is used to drive v out and the quiescent current of the switching regulator. to ensure that the usb speci? cation is strictly met, both components of the input current should be considered. the electrical characteristics table gives the typical values for quiescent currents in all settings as well as current limit programming accuracy. to get as close to the 500ma or 100ma speci? cations as possible, a precision resistor should be used. recall that: i vbus = i vbusq + v clprog /r clpprog ? (h clprog +1). an averaging capacitor is required in parallel with the resistor so that the switching regulator can determine the average input current. this capacitor also provides the dominant pole for the feedback loop when current limit is reached. to ensure stability, the capacitor on clprog should be 0.1f or larger. bidirectional powerpath switching regulator inductor selection because the input voltage range and output voltage range of the powerpath switching regulator are both fairly nar- row, the ltc3576/ltc3576-1 were designed for a speci? c inductance value of 3.3h. some inductors which may be suitable for this application are listed in table 7. table 7. recommended powerpath inductors for the ltc3576 inductor type l (h) max i dc (a) max dcr () size in mm (l w h) manufacturer lps4018 3.3 2.2 0.08 3.9 3.9 1.7 coilcraft www.coilcraft.com d53lc db318c 3.3 3.3 2.26 1.55 0.034 0.070 5 5 3 3.8 3.8 1.8 toko www.toko.com we-tpc type m1 3.3 1.95 0.065 4.8 4.8 1.8 wurth electronik www.we-online.com cdrh6d12 cdrh6d38 3.3 3.3 2.2 3.5 0.063 0.020 6.7 6.7 1.5 7 7 4 sumida www.sumida.com bidirectional powerpath switching regulator v bus and v out bypass capacitor selection the type and value of capacitors used with the ltc3576/ ltc3576-1 determine several important parameters such as regulator control-loop stability and input voltage ripple. because the ltc3576/ltc3576-1 use a bidirectional switching regulator between v bus and v out , the v bus current waveform contains high frequency components. it is strongly recommended that a low equivalent series resistance (esr) multilayer ceramic capacitor (mlcc) be used to bypass v bus . tantalum and aluminum capacitors are not recommended because of their high esr. the value of the capacitor on v bus directly controls the amount of input ripple for a given load current. increasing the size of this capacitor will reduce the input ripple. the inrush current limit speci? cation for usb devices is calculated in terms of the total number of coulombs needed to charge the v bus bypass capacitor to 5v. the maximum inrush charge for usb on-the-go devices is 33c. this places a limit of 6.5f of capacitance on v bus assuming a linear capacitor. however, most ceramic capacitors have a capacitance that varies with bias voltage. the average capacitance needs to be less than 6.5f over a 0v to 5v bias voltage range to meet the inrush current limit speci? cation. a 10f capacitor in a 0805 package, such as the murata grm21br71a106ke51l would be a suitable v bus bypass capacitor. if more capacitance is required for better noise performance and stability it should be connected directly to the v bus pin when using the overvoltage protection circuit. this extra capacitance will be soft-connected over several milliseconds to limit inrush current and avoid excessive transient voltage drops on v bus . to prevent large v out voltage steps during transient load conditions, it is also recommended that an mlcc be used to bypass v out . the output capacitor is used in the com- pensation of the switching regulator. at least 10f with low esr are required on v out . additional capacitance will improve load transient performance and stability. mlccs typically have exceptional esr performance. mlccs combined with a tight board layout and an unbroken ground plane will yield very good performance and low emi emissions.
ltc3576/ltc3576-1 34 3576fb applications information there are mlccs available with several types of dielectrics each having considerably different characteristics. for example, x7r mlccs have the best voltage and tempera- ture stability. x5r mlccs have apparently higher packing density but poorer performance over their rated voltage and temperature ranges. y5v mlccs have the highest packing density, but must be used with caution, because of their extreme nonlinear characteristic of capacitance versus voltage. the actual in-circuit capacitance of a ceramic capacitor should be measured with a small ac signal and dc bias as is expected in-circuit. many vendors specify the capacitance versus voltage with a 1v rms ac test signal and, as a result, over state the capacitance that the capacitor will present in the application. using similar operating conditions as the application, the user must measure or request from the vendor the actual capacitance to determine if the selected capacitor meets the minimum capacitance that the application requires. step-down switching regulator output voltage programming all three switching regulators have i 2 c programmable set points and can be programmed for start-up output voltages of at least 0.8v. the full-scale output voltage for each switching regulator is programmed using a resistor divider from the switching regulator output connected to the fbx pins such that: v outx = v fbx r1 r2 + 1 ? ? ? ? ? ? where v fbx ranges from 0.425v to 0.8v. see figure 5. typical values for r1 are in the range of 40k to 1m. the capacitor c fb cancels the pole created by feedback resistors and the input capacitance of the fbx pin and also helps to improve transient response for output voltages much greater than 0.8v. a variety of capacitor sizes can be used for c fb but a value of 10pf is recommended for most ap- plications. experimentation with capacitor sizes between 2pf and 22pf may yield improved transient response. step-down switching regulator inductor selection many different sizes and shapes of inductors are avail- able from numerous manufacturers. choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. the general purpose step-down converters are designed to work with inductors in the range of 2h to 10h. for most applications a 4.7h inductor is suggested for the lower current switching regulators 1 and 2 and 2h is recom- mended for the higher current switching regulator 3. larger value inductors reduce ripple current which improves out- put ripple voltage. lower value inductors result in higher ripple current and improved transient response time. to maximize ef? ciency, choose an inductor with a low dc resistance. for a 1.2v output, ef? ciency is reduced about 2% for 100m series resistance at 400ma load current, and about 2% for 300m series resistance at 100ma load current. choose an inductor with a dc current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. if output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current speci? ed for the step-down converters. different core materials and shapes will change the size/current and price/current relationship of an inductor. toroid or shielded pot cores in ferrite or permalloy materials are small and dont radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. inductors that are very thin or have a very small volume typically have much higher core and dcr losses, and will not give the best ef? ciency. the choice of which style inductor to use often depends more on the price vs size, performance and any radiated emi requirements than on what the ltc3576/ltc3576-1 require to operate. v inx ltc3576/ ltc3576-1 l swx r1 c out c fb v outx r2 3576 f05 fbx gnd figure 5. buck converter application circuit
ltc3576/ltc3576-1 35 3576fb the inductor value also has an effect on burst mode op- eration. lower inductor values will cause the burst mode operation switching frequency to increase. table 8 shows several inductors that work well with the ltc3576/ltc3576-1s general purpose regulators. these inductors offer a good compromise in current rating, dcr and physical size. consult each manufacturer for detailed information on their entire selection of inductors. table 8. recommended inductors inductor type l (h) max i dc (a) max dcr () size in mm (l w h) manufacturer de2818c d312c de2812c 4.7 3.3 4.7 3.3 2.2 4.7 3.3 2.0 1.25 1.45 0.79 0.90 1.14 1.2 1.4 1.8 0.072 0.053 0.24 0.20 0.14 1.13* 0.10* 0.067* 3.0 2.8 1.8 3.0 2.8 1.8 3.6 3.6 1.2 3.6 3.6 1.2 3.6 3.6 1.2 3.0 2.8 1.2 3.0 2.8 1.2 3.0 2.8 1.2 toko www.toko.comm cdrh3d16 cdrh2d11 cls4d09 4.7 3.3 2.2 4.7 3.3 2.2 4.7 0.9 1.1 1.2 0.5 0.6 0.78 0.75 0.11 0.085 0.072 0.17 0.123 0.098 0.19 4.0 4.0 1.8 4.0 4.0 1.8 4.0 4.0 1.8 3.2 3.2 1.2 3.2 3.2 1.2 3.2 3.2 1.2 4.9 4.9 1.0 sumida www.sumida.com sd3118 sd3112 sd12 sd10 4.7 3.3 2.2 4.7 3.3 2.2 4.7 3.3 2.2 4.7 3.3 2.2 1.3 1.59 2.0 0.8 0.97 1.12 1.29 1.42 1.80 1.08 1.31 1.65 0.162 0.113 0.074 0.246 0.165 0.14 0.117* 0.104* 0.075* 0.153* 0.108* 0.091* 3.1 3.1 1.8 3.1 3.1 1.8 3.1 3.1 1.8 3.1 3.1 1.2 3.1 3.1 1.2 3.1 3.1 1.2 5.2 5.2 1.2 5.2 5.2 1.2 5.2 5.2 1.2 5.2 5.2 1.0 5.2 5.2 1.0 5.2 5.2 1.0 cooper www.cooperet.com lps3015 4.7 3.3 2.2 1.1 1.3 1.5 0.2 0.13 0.11 3.0 3.0 1.5 3.0 3.0 1.5 3.0 3.0 1.5 coilcraft www.coilcraft.com *typical dcr step-down switching regulator input/output bypass capacitor selection low esr (equivalent series resistance) mlccs should be used at each switching regulator output as well as at each switching regulator input supply (v inx ). only x5r or x7r ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. a 10f output capaci- applications information tor is suf? cient for most applications. for good transient response and stability the output capacitor should retain at least 4f of capacitance over operating temperature and bias voltage. each switching regulator input supply should be bypassed with a 1f capacitor. consult with capacitor manufacturers for detailed information on their selection and speci? cations of ceramic capacitors. many manufac- turers now offer very thin (<1mm tall) ceramic capacitors ideal for use in height-restricted designs. table 9 shows a list of several ceramic capacitor manufacturers. table 9. recommended ceramic capacitor manufacturers avx www.avxcorp.com murata www.murata.com taiyo yuden www.t-yuden.com vishay siliconix www.vishay.com tdk www.tdk.com overvoltage protection v bus can be protected from overvoltage damage with two additional components, a resistor r1 and an n-channel mosfet mn1, as shown in figure 6. suitable choices for mn1 are listed in table 10. table 10. recommended n-channel mosfets for the overvoltage protection circuit part number bvdss r on package si1472dh 30v 82m sc70-6 si2302ads 20v 60m sot-23 si2306bds 30v 65m sot-23 si2316bds 30v 80m sot-23 irlml2502 20v 35m sot-23 fdn372s 30v 50m sot-23 ntljs4114n 30v 35m wdfn6 r1 is a 6.2k resistor and must be rated for the power dis- sipated during maximum overvoltage. in an overvoltage condition the ovsens pin will be clamped at 6v. r1 must be sized appropriately to dissipate the resultant power. for example, a 1/10w 6.2k resistor can have at most p max ? 6.2k = 25v applied across its terminals. with the 6v at ovsens, the maximum overvoltage magnitude that this resistor can withstand is 31v. a 1/4w 6.2k resistor raises this value to 45v. ovsenss absolute maximum current rating of 10ma imposes an upper limit of 68v protection.
ltc3576/ltc3576-1 36 3576fb transforms the voltage at v bus to a voltage just above the level at bat, while limiting power to less than the amount programmed at clprog. the charger should be programmed (with the prog pin) to deliver the maximum safe charging current without regard to the usb speci? - cations. if there is insuf? cient current available to charge the battery at the programmed rate, it will reduce charge current until the system load on v out is satis? ed and the v bus current limit is satis? ed. programming the charger for more current than is available will not cause the aver- age input current limit to be violated. it will merely allow the battery charger to make use of all available power to charge the battery as quickly as possible, and with minimal dissipation within the charger. battery charger stability considerations the ltc3576/ltc3576-1s battery charger contains both a constant-voltage and a constant-current control loop. the constant-voltage loop is stable without any compensation when a battery is connected with low impedance leads. excessive lead length, however, may add enough series inductance to require a bypass capacitor of at least 1f from bat to gnd. high value, low esr mlccs reduce the constant-voltage loop phase margin, possibly resulting in instability. up to 22f may be used in parallel with a battery, but larger capacitors should be decoupled with 0.2 to 1 of series resistance. furthermore, a 100f mlcc in series with a 0.3 resistor from bat to gnd is required to prevent oscillation when the battery is disconnected. in constant-current mode, the prog pin is in the feed- back loop rather than the battery voltage. because of the additional pole created by any prog pin capacitance, applications information r1 usb/wall adapter 3576 f06 c1 mn1 v bus ovsens ovgate ltc3576/ ltc3576-1 figure 6. overvoltage protection figure 8. dual polarity voltage protection r1 c1 d1 v1 v2 d2 m1 m2 3576 f07 wall ovsens ovgate ltc3576/ ltc3576-1 v bus gnd figure 7. dual-input overvoltage protection i t is possible to protect both v bus and wall from overvoltage damage with several additional components, as shown in figure 7. schottky diodes d1 and d2 pass the larger of v1 and v2 to r1 and ovsens. if either v1 or v2 exceeds 6v plus v f (schottky), ovgate will be pulled to gnd and both the wall and usb inputs will be protected. each input is protected up to the drain-source breakdown, bvdss, of mn1 and mn2. r1 must also be rated for the power dissipated during maximum overvoltage. reverse voltage protection the ltc3576/ltc3576-1 can also be easily protected against the application of reverse voltages, as shown in figure 8. d1 and r1 are necessary to limit the maximum v gs seen by mp1 during positive overvoltage events. d1s breakdown voltage must be safely below mp1s bvgs. the circuit shown in figure 8 offers forward voltage protection up to mn1s bvdss and reverse voltage protection up to mp1s bvdss. battery charger over programming the usb high power speci? cation allows for up to 2.5w to be drawn from the usb port. the ltc3576/ltc3576-1s bidirectional switching regulator in step-down mode r2 r1 usb/wall adapter 3576 f08 c1 d1 mn1 mp1 v bus positive protection up to bvdss of mn1 v bus negative protection up to bvdss of mp1 v bus ovsens ovgate ltc3576/ ltc3576-1
ltc3576/ltc3576-1 37 3576fb capacitance on this pin must be kept to a minimum. with no additional capacitance on the prog pin, the charger is stable with program resistor values as high as 25k. however, additional capacitance on this node reduces the maximum allowed program resistor. the pole frequency at the prog pin should be kept above 100khz. therefore, if the prog pin has a parasitic capacitance, c prog , the fol- lowing equation should be used to calculate the maximum resistance value for r prog : r prog 1 2 ? 100khz ? c prog alternate ntc thermistors and biasing the ltc3576/ltc3576-1 provide temperature quali? ed charging if a grounded thermistor and a bias resistor are connected to ntc. by using a bias resistor whose value is equal to the room temperature resistance of the thermistor (r25) the upper and lower temperatures are pre-programmed to approximately 40c and 0c respec- tively assuming a vishay curve 1 thermistor. the upper and lower temperature thresholds can be ad- justed by either a modi? cation of the bias resistor value or by adding a second adjustment resistor to the circuit. if only the bias resistor is adjusted, then either the upper or the lower threshold can be modi? ed but not both. the other trip point will be determined by the characteristics of the thermistor. using the bias resistor in addition to an adjustment resistor, both the upper and the lower tempera- ture trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. examples of each technique are given below. ntc thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. the vishay-dale thermistor nths0603n011-n1003f, used in the following examples, has a nominal value of 100k and follows the vishay curve 1 resistance-temperature characteristic. in the explanation below, the following notation is used. r25 = value of the thermistor at 25c r ntc|cold = value of thermistor at the cold trip point r ntc|hot = value of the thermistor at the hot trip point r cold = ratio of r ntc|cold to r25 r hot = ratio of r ntc|hot to r25 r nom C primary thermistor bias resistor (see figure 9) r1 = optional temperature range adjustment resistor (see figure 10) applications information figure 9. standard ntc con? guration figure 10. modi? ed ntc con? guration C + C + r nom 100k r ntc 100k ntc ntcbias 0.1v ntc_enable 3576 f09 ltc3576/ltc3576-1 ntc block too_cold too_hot 0.765 ? ntcbias 0.349 ? ntcbias C + 3 4 t C + C + r nom 105k r ntc 100k r1 12.7k ntc ntcbias 0.1v ntc_enable 3576 f10 ltc3576/ltc3576-1 ntc block too_cold too_hot 0.765 ? ntcbias 0.349 ? ntcbias C + 3 4 t
ltc3576/ltc3576-1 38 3576fb the trip points for the ltc3576/ltc3576-1s temperature quali? cation are internally programmed at 0.349 ? ntcbias for the hot threshold and 0.765 ? ntcbias for the cold threshold. therefore, the hot trip point is set when: r ntc hot r nom + r ntc hot ? ntcbias = 0.349 ? ntcbias and the cold trip point is set when: r ntc cold r nom + r ntc cold ? ntcbias = 0.765 ? ntcbias solving these equations for r ntc|cold and r ntc|hot results in the following: r ntc|hot = 0.536 ? r nom and r ntc|cold = 3.25 ? r nom by setting r nom equal to r25, the above equations result in r hot = 0.536 and r cold = 3.25. referencing these ratios to the vishay resistance-temperature curve 1 chart gives a hot trip point of about 40c and a cold trip point of about 0c. the difference between the hot and cold trip points is approximately 40c. by using a bias resistor, r nom , different in value from r25, the hot and cold trip points can be moved in either direction. the temperature span will change somewhat due to the nonlinear behavior of the thermistor. the fol- lowing equations can be used to calculate a new value for the bias resistor: r nom = r hot 0.536 ?r25 r nom = r cold 3.25 ?r25 where r hot and r cold are the resistance ratios at the de- sired hot and cold trip points. note that these equations are linked. therefore, only one of the two trip points can be chosen, the other is determined by the default ratios designed in the ic. consider an example where a 60c hot trip point is desired. from the vishay curve 1 r-t characteristics, r hot is 0.2488 at 60c. using the above equation, r nom should be set to 46.4k. with this value of r nom , r cold is 1.436 and the cold trip point is about 16c. notice that the span is now 44c rather than the previous 40c. this is due to the decrease in temperature gain of the thermistor as absolute temperature increases. the upper and lower temperature trip points can be inde- pendently programmed by using an additional bias resistor as shown in figure 10. the following formulas can be used to compute the values of r nom and r1: r nom = r cold ?r hot 2.714 ?r25 r1 = 0.536 ? r nom ?r hot ?r25 for example, to set the trip points to 0c and 45c with a vishay curve 1 thermistor choose: r nom = 3.266 ? 0.4368 2.714 ? 100k = 104.2k the nearest 1% value is 105k: r1 = 0.536 ? 105k C 0.4368 ? 100k = 12.6k the nearest 1% value is 12.7k. the ? nal solution is shown in figure 10 and results in an upper trip point of 45c and a lower trip point of 0c. hot plugging and usb inrush current limiting the overvoltage protection circuit provides inrush current limiting due to the long time it takes for ovgate to fully enhance the n-channel mosfet. this prevents the current from building up in the cable too quickly thus dampen- ing out any resonant overshoot on v bus . it is possible to observe voltage overshoot on v bus when connecting the ltc3576/ltc3576-1 to a lab power supply if the overvoltage protection circuit is not used. this overshoot is caused by the inductance of the long leads from the power supply to v bus . twisting the wires together from the supply to v bus can greatly reduce the parasitic inductance of these long leads keeping the voltage at v bus to safe levels. usb cables are generally manufactured with the power leads in close proximity, and thus have fairly low parasitic inductance. applications information
ltc3576/ltc3576-1 39 3576fb hot plugging and usb on-the-go if there is more than 4.3v on v bus when on-the-go is enabled, the bidirectional switching regulator will not try to drive v bus . if usb on-the-go is enabled and an external supply is then connected to v bus , one of three things will happen depending on the properties of the external sup- ply. if the external supply has a regulation voltage higher than 5.1v, the bidirectional switching regulator will stop switching and v bus will be held at the regulation voltage of the external supply. if the external supply has a lower regulation voltage and is capable of only sourcing current then v bus will be regulated to 5.1v. the external supply will not source current to v bus . for a supply that can also sink current and has a regula- tion voltage less than 5.1v, the bidirectional switching regulator will source current into the external supply in an attempt to bring v bus up to 5.1v. as long as the external supply holds v bus to more than 4v or v out + 70mv, the bidirectional switching regulator will source up to 680ma into the supply. if v bus is held to a voltage that is less than 4v and v out + 70mv then the short circuit timer will shut off the switching regulator after 7.2ms. the chrg pin will then blink indicating a short circuit current fault. v bus bypass capacitance and usb on-the-go session request protocol when two on-the-go devices are connected, one will be the a device and the other will be the b device depending on whether the device is connected to a micro a or micro b plug. the a device provides power to the b device and starts as the host. to prolong battery life, the a device can power down v bus when the bus is not being used. if the a device has powered down v bus , the b device can request the a device to power up v bus and start a new session us- ing the session request protocol (srp). the srp consists of data-line pulsing and v bus pulsing. the b device must ? rst pulse the d + or d C data line. the b device must then pulse v bus only if the a device does not respond to the data-line pulse. the a device is required to respond to only one of the pulsing methods. a devices that never power down v bus are not required to respond to the srp . applications information for v bus pulsing, the limit on the v bus capacitance on the a device allows a b device to differentiate between a powered down on-the-go device and a powered down standard host. the b device will send out a pulse of current that will raise v bus to a voltage between 2.1v and 5.25v if connected to an on-the-go a device which must have no more than 6.5f. an on-the-go a device must drive v bus as soon as the current pulse raises v bus above 2.1v if the device is capable of responding to v bus pulsing. this same current pulse must not raise v bus any higher than 2v when connected to a standard host which must have at least 96f. the 96f for a standard host represents the minimum capacitance with v bus between 4.75v and 5.25v. since the srp pulse must not drive v bus greater than 2v, the capacitance seen at these voltage levels can be greater than 96f, especially if mlccs are used. therefore, the 96f represents a lower bound on the standard host bypass capacitance for determining the amplitude and duration of the current pulse. more capacitance will only decrease the maximum level that v bus will rise to for a given current pulse. figure 11 shows an on-the-go device using the ltc3576/ ltc3576-1 acting as the a device. additional capacitance can be placed on the v bus pin of the ltc3576/ltc3576-1 when using the overvoltage protection circuit. a b device may not be able to distinguish between a powered down ltc3576/ltc3576-1 with overvoltage protection and a powered down standard host because of this extra ca- pacitance. in addition, if the srp pulse raises v bus above its uvlo threshold of 4.3v the ltc3576/ltc3576-1 will assume input power is available and will not attempt to drive v bus . therefore, it is recommended that an on- the-go device using the ltc3576/ltc3576-1 respond to data-line pulsing. when an on-the-go device using the ltc3576/ltc3576-1 becomes the b device, as in figure 12, it must send out a data line pulse followed by a v bus pulse to request a session from the a device. the on-the-go device designer can choose how much capacitance will be placed on the v bus pin of the ltc3576/ltc3576-1 and then generate a v bus pulse that can distinguish between a powered
ltc3576/ltc3576-1 40 3576fb down on-the-go a device and a powered down standard host. a suitable pulse can be generated because of the disparity in the bypass capacitances of an on-the-go a device and a standard host even if there is somewhat more than 6.5f capacitance connected to the v bus pin of the ltc3576/ltc3576-1. board layout considerations the exposed pad on the backside of the ltc3576/ ltc3576-1 package must be securely soldered to the pc board ground. this is the primary ground pin in the pack- age, and it serves as the return path for both the control circuitry and the n-channel mosfet switches. furthermore, due to its high frequency switching circuitry, it is imperative that the input capacitor, inductor, and output capacitor be as close to the ltc3576/ltc3576-1 as possible and that there be an unbroken ground plane under the ltc3576/ltc3576-1 and all of their external applications information on-the-go power manager on-the-go transceiver b device 3576 f11 a device d + d C ovsens ovgate v bus c b <6.5f c a <6.5f without ovp ovp (optional) on-the-go transceiver ltc3576 / ltc3576-1 enotg figure 11. ltc3576/ltc3576-1 as the a device standard usb host or on-the-go power manager standard or on-the-go transceiver a device 3576 f12 b device d + d C ovsens ovgate v bus c a <6.5f for otg devices >96f for standard host c b <6.5f without ovp ovp (optional) on-the-go transceiver ltc3576 / ltc3576-1 enotg figure 12. ltc3576/ltc3576-1 as the b device high frequency components. high frequency currents, such as the v bus , v in1 , v in2 and v in3 currents tend to ? nd their way on the ground plane along a mirror path directly beneath the incident path on the top of the board. if there are slits or cuts in the ground plane due to other traces on that layer, the current will be forced to go around the slits. if high frequency currents are not allowed to ? ow back through their natural least-area path, excessive voltage will build up and radiated emissions will occur (see figure 13). there should be a group of vias directly under the grounded backside leading directly down to an internal ground plane. to minimize parasitic inductance, the ground plane should be as close as possible to the top plane of the pc board (layer 2). the idgate pin for the external ideal diode controller has extremely limited drive current. care must be taken to minimize leakage to adjacent pc board traces. 100na of leakage from this pin will introduce an additional offset to
ltc3576/ltc3576-1 41 3576fb the ideal diode of approximately 10mv. to minimize leakage, the trace can be guarded on the pc board by surrounding it with v out connected metal, which should generally be less than one volt higher than idgate. when laying out the printed circuit board, the following checklist should be used to ensure proper operation of the ltc3576/ltc3576-1: 1. the exposed pad of the package (pin 39) should connect directly to a large ground plane to minimize thermal and electrical impedance. 2. the traces connecting v bus , v in1 , v in2 , v in3 and v in of the external step-down switching regulator to their respective decoupling capacitors should be as short as possible. the gnd side of these capaci- tors should connect directly to the ground plane of the part. these capacitors provide the ac current to the internal power mosfets and their drivers. it is critical to minimize inductance from these capacitors to the ltc3576/ltc3576-1 and external step-down switching regulator. 3. connections between the step-down switching regu- lator (both internal and external) inductors and their respective output capacitors should be kept as short figure 13. higher frequency ground current follow their incident path. slices in the ground plane create large loop areas. the large loop areas increase the inductance of the path leading to higher system noise applications information 3576 f13 as possible. use area ? lls whenever possible. this also applies to the powerpath switching regulator inductor and the output capacitor on v out . the gnd side of the output capacitors should connect directly to the thermal ground plane of the part. 4. the switching power traces connecting sw, sw1, sw2, sw3 and the switch node of the external step- down switching regulator to their respective induc- tors should be minimized to reduce radiated emi and parasitic coupling. due to the large voltage swing of the switching nodes, sensitive nodes such as the feedback nodes (fb1, fb2 and fb3) should be kept far away or shielded from the switching nodes or poor performance could result. 5. keep the feedback pin traces (fb1, fb2, fb3 and fb of the external step-down switching regulator) as short as possible. minimize any parasitic capacitance between the feedback traces and any switching node (i.e., sw, sw1, sw2, sw3 and logic signals). if nec- essary shield the feedback nodes with a gnd trace 6. connect v in1 , v in2 and v in3 to v out through a short low impedance trace.
ltc3576/ltc3576-1 42 3576fb typical applications minimum parts count usb power manager with low-battery start-up and usb on-the-go + v bus sw 35 36 v bus v out 34 dv cc 12 13, 14 ovgate c1 10f 0805 1f c2 0.1f 0402 c3 22f 0805 usb, wall adapter usb on-the-go ovsens 6 ntcbias 3 prog 29 clprog 1 ldo3v3 2 chrg 30 3.01k 1.02m 1.76v to 3.3v 400ma 1.61v to 3.03v 400ma 0.8v to 1.51v 1a 324k 10pf li-ion 1f to other loads 1f 1f 10f 1k ntc 4 5 en1 10 en2 22 en3 enotg 11 i lim0 37 i lim1 38 19 33 idgate 31 v in1 8 sw1 9 fb1 7 bat 32 26 27 28 v c wall ltc3576/ltc3576-1 l1 3.3h l2 4.7h acpr 1.02m 365k 10pf 10f v in2 24 sw2 23 fb2 i 2 c 25 l3 4.7h 751k 806k c1: murata grm21br7a106ke51l c3: taiyo yuden jmk212bj226mg l1: coilcraft lps4018-332lm l2, l3: toko 1098as-4r7m l4: toko 1098as-2r0m 10k 3576 ta02 10pf 10f v in3 16 sw3 17 fb3 20 rst3 21 l4 2h memory pushbutton microcontroller microprocessor i/o core por
ltc3576/ltc3576-1 43 3576fb typical applications high ef? ciency usb/automotive power manager with overvoltage protection, reverse-voltage protection, low-battery start-up and usb on-the-go + v bus sw 35 36 m4 m5 v bus v out 34 dv cc 12 13, 14 ovgate c1 22f 0805 4.7f 22f 0.47f d1 1f c2 0.1f 0402 c3 22f 0805 li-ion usb, wall adapter ovsens 6 ntcbias 3 prog 29 clprog 1 ldo3v3 2 3.01k 1.02m 2.2k 1.76v to 3.3v 400ma 1.61v to 3.03v 400ma 0.8v to 1.51v 1a 324k 10pf 1f to other loads 1f 1f 10f 1k t 100k r2 100k r1 6.2k ntc 4 5 en1 10 en2 22 en3 enotg 11 i lim0 37 i lim1 38 19 33 idgate 31 v in1 8 chrg 30 sw1 9 fb1 7 bat 32 26 9 7 10 5 4 11 1 6 2 3 8 27 28 v c wall ltc3576/ltc3576-1 l2 3.3h l1 6.8h l3 4.7h acpr 1.02m 365k 10pf 10f v in2 24 sw2 23 fb2 i 2 c 25 l4 4.7h 751k 806k c1, c3: tayio yuden jmk212bj226mg d1: diodes inc. dfls240l l1: taiyo yuden np06dzb6r8m l2: coilcraft lps4018-332lm l3, l4: toko 1098as-4r7m l5: toko 1098as-2r0m m1,m2,m4, m5: siliconix si2333ds m3: on semiconductor ntljs4114n r1: 1/10w resistor r2: curve 1 10k 3576 ta03 10pf 10f v in3 16 sw3 17 fb3 20 rst3 21 l5 2h memory pushbutton microcontroller microprocessor i/o core por v c pg 40.2k m2 m1 m3 68nf automotive firewire, etc. 150k gnd bd sync fb 499k 100k r t run/ss lt3480 v in boost sw usb on-the-go
ltc3576/ltc3576-1 44 3576fb typical applications high ef? ciency usb/automotive power manager with overvoltage protection, usb on-the-go, pushbutton start, automatic supply sequencing and 10 second push-and-hold hard shutdown + v bus sw 35 36 m2 m3 v bus v out 34 ovgate c1 22f 0805 4.7f 22f 0.47f d1 c2 0.1f 0402 10f 10f c3 22f 0805 li-ion usb, wall adapter ovsens 6 ntcbias 3 prog 29 clprog 1 14 13 12 38 37 11 3.01k 1f 1f 1k 1.02m 2.2k 1.76v to 3.3v 400ma 0.8v to 1.51v 1a 1.61v to 3.03v 400ma send i 2 c code: 0 s 1201f8 324k 10pf 1f to other loads 1f 1f 10f 1k t 100k r2 100k r1 6.2k ntc 4 5 en3 sda enotg i lim0 i lim1 33 idgate 31 v in1 8 chrg 30 sw1 9 fb1 7 bat 32 26 9 7 10 5 4 11 1 6 2 3 8 27 28 v c wall ltc3576/ltc3576-1 l2 3.3h l1 6.8h l3 4.7h acpr 751k 10k 806k 10pf 10f v in3 en2 16 sw3 scl dv cc 2 ldo3v3 17 22 en1 10 fb3 20 l5 2h 1.02m 365k 5.1k 5.1k c1, c3: tayio yuden jmk212bj226mg d1: diodes inc. dfls240l l1: taiyo yuden np06dzb6r8m l2: coilcraft lps4018-332lm l3, l4: toko 1098as-4r7m l5: toko 1098as-2r0m m1: on semiconductor ntljs4114n m2, m3: siliconix si2333ds m4: 2n7002 r1: 1/10w resistor r2: curve 1 3576 ta04 10pf 10f v in2 24 sw2 23 fb2 25 rst3 21 l4 4.7h memory core por i/o sda scl v c pg 40.2k m1 68nf automotive firewire, etc. 150k gnd bd sync fb 499k 100k r t run/ss lt3480 v in boost sw 4.7k 10k 1m m4 usb on-the-go
ltc3576/ltc3576-1 45 3576fb typical applications high ef? ciency usb/automotive power manager with current limiting and overvoltage protection on both inputs, low-battery start-up and usb on-the-go + v bus sw 35 36 v bus v out 34 dv cc 12 13, 14 ovgate c1 22f 0805 4.7f 22f 0.47f 1f c2 0.1f 0402 c3 22f 0805 li-ion usb, wall adapter ovsens 6 ntcbias 3 prog 29 clprog 1 ldo3v3 2 chrg 30 3.01k 1.02m 1.76v to 3.3v 400ma 1.61v to 3.03v 400ma 0.8v to 1.51v 1a 324k 10pf 1f to other loads 1f 1f 10f 1k t 100k r2 100k r1 6.2k ntc 4 5 en1 10 en2 22 en3 enotg 11 i lim0 37 i lim1 38 19 33 idgate 31 v in1 8 sw1 9 fb1 7 bat 32 26 4 3 1 92 7 8 6 d1 5 27 28 v c wall ltc3576/ltc3576-1 l2 3.3h l1 4.7h l3 4.7h acpr 1.02m 365k 10pf 10f v in2 24 sw2 23 fb2 i 2 c 25 l4 4.7h 751k 806k c1, c3: tayio yuden jmk212bj226mg d1: diodes inc. dfls140 l1: coilcraft mss6132-472mlc l2: coilcraft lps4018-332lm l3, l4: toko 1098as-4r7m l5: toko 1098as-2r0m m1: fairchild fdn327s r1: 1/10w resistor r2: curve 1 10k 3576 ta05 10pf 10f v in3 16 sw3 17 fb3 20 rst3 21 l5 2h memory pushbutton microcontroller microprocessor i/o core por v c 34.2k m1 automotive firewire, etc. 7.5v to 36v transients to 60v gnd hvok i sense v out i lim lt3653 v in boost sw usb on-the-go
ltc3576/ltc3576-1 46 3576fb typical applications high ef? ciency usb/wall power manager with dual overvoltage protection, reverse-voltage protection, low-battery start-up and usb on-the-go + v bus sw 35 36 m5 m6 v bus v c v out 34 dv cc 12 13, 14 c2 22f 0805 c1 22f 0805 1f c3 0.1f 0402 c4 22f 0805 li-ion usb ovsens 6 ntcbias 3 prog 29 clprog 1 ldo3v3 2 3.01k 1.02m 2.2k 1.76v to 3.3v 400ma 1.61v to 3.03v 400ma 0.8v to 1.51v 1a 324k 10pf 1f to other loads 1f 1f 10f 1k t 100k r2 100k r1 6.2k ntc 4 26 en1 10 en2 22 en3 enotg 11 i lim0 37 i lim1 38 19 33 idgate 31 v in1 8 chrg 30 sw1 9 fb1 7 bat 32 27 528 wall ovgate ltc3576/ltc3576-1 l1 3.3h l2 4.7h acpr 1.02m 365k 10pf 10f v in2 24 sw2 23 fb2 i 2 c 25 l3 4.7h 751k 806k c1, c2, c4: tayio yuden jmk212bj226mg l1: coilcraft lps4018-332lm l2, l3: toko 1098as-4r7m l4: toko 1098as-2r0m m1, m2, m5, m6: siliconix si2333ds m3, m4: fairchild fdn327s r1: 1/10w resistor r2: curve 1 10k 3576 ta07 10pf 10f v in3 16 sw3 17 fb3 20 rst3 21 l4 2h memory pushbutton microcontroller microprocessor i/o core por m2 m1 m4 m3 5v wall adapter usb on-the-go
ltc3576/ltc3576-1 47 3576fb information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description ufe package 38-lead plastic qfn (4mm 6mm) (reference ltc dwg # 05-08-1750 rev b) 4.00 0.10 2.40 ref 6.00 0.10 note: 1. drawing is not a jedec package outline 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 0.10 38 37 1 2 bottom viewexposed pad 4.40 ref 0.75 0.05 r = 0.115 typ r = 0.10 typ pin 1 notch r = 0.30 or 0.35 45 chamfer 0.20 0.05 0.40 bsc 0.200 ref 0.00 C 0.05 (ufe38) qfn 0708 rev b recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.20 0.05 0.40 bsc 2.40 ref 4.40 ref 5.10 0.05 6.50 0.05 2.65 0.05 3.10 0.05 4.50 0.05 package outline 2.65 0.10 4.65 0.10 4.65 0.05
ltc3576/ltc3576-1 48 3576fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2008 lt 0809 rev b ? printed in usa related parts typical application + v bus sw 35 36 v bus v out 34 ovgate c1 22f 0805 c2 22f 0805 c3 0.1f 0402 li-ion ovsens 6 ldo3v3 1f 300k 2 enotg 11 3.01k 1k to other loads m2 6.2k to usb transceiver 5 33 prog bat 32 29 clprog 1 26 28 27 v c wall ltc3576/ltc3576-1 v bus powers up when id pin has less than 10 to gnd (micro-a plug connected) l2 3.3h acpr 3576 ta06 m1 j1 micro-ab v bus d C d + id gnd c1, c2: taiyo yuden jmk212bj226mg d1: diodes inc. dfls140 j1: hirose zx62-ab-5pa l1: coilcraft mss6132-472mlc l2: coilcraft lps4018-332lm m1: fairchild fdn372s m2: siliconix si2333ds 4.7f 22f 0.47f 4 3 1 92 7 8 6 d1 5 l1 4.7h v c 34.2k automotive firewire, etc. 7.5v to 36v transients to 60v gnd hvok i sense v out i lim lt3653 v in boost sw usb on-the-go firewire/automotive battery charger with automatic usb on-the-go and overvoltage protection part number description comments power management ltc3555/ltc3555-1 ltc3555-3 switching usb power manager with li-ion/polymer chargers plus triple buck dc/dc maximizes available power from usb port, bat-track, 1.5a max charge current, 180m ideal diode with <50m option, 3.3v/25ma always-on ldo, two 400ma and one 1a buck regulators, instant-on operation (ltc3555-1), instant-on operation and 4.1v float votlage (ltc3555-3), 4mm 5mm 28-pin qfn package ltc3556 switching usb power manager with li-ion/polymer charger plus dual buck plus buck-boost dc/dc maximizes available power from usb port, bat-track, instant-on operation, 1.5a max charge current, 180m ideal diode with <50m option, 3.3v/25ma always-on ldo, two 400ma buck regulators, one 1a buck-boost regulator, 4mm 5mm 28-pin qfn package ltc3586 switching usb power manager with li-ion/polymer charger plus dual buck plus buck-boost plus boost dc/dc maximizes available power from usb port, bat-track, instant-on operation, 1.5a max charge current, 180m ideal diode with <50m option, 3.3v/25ma always-on ldo, two 400ma synchronous buck regulators, one 1a buck-boost regulator, one 600ma boost regulator, 4mm 6mm 38-pin qfn package ltc4098/ltc4098-1 switching usb power manager and battery chargers with overvoltage protection maximizes available power from usb port, bat-track, instant-on operation, 1.5a max charge current, 180m ideal diode with <50m option, controller for external high voltage buck regulator, protection against transients of up to 60v, 3.3v/25ma always-on ldo,4.1v float voltage (ltc4098-1), 4mm 3mm 14-pin dfn package

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