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1 ? fn6498.3 isl6252, isl6252a highly integrated battery charger controller for notebook computers the isl6252, isl6252a is a highly integrated battery charger controller for li-ion/li-ion polymer batteries. high efficiency is achieved by a synchronous buck topology. the low side mosfet emulates a diode at light loads to improve the light load efficiency and prevent system bus boosting. the constant output voltage can be selected for 2, 3 and 4 series li-ion cells with 0.5% accuracy over-temperature. it can also be programmed between 4.2v + 5%/cell and 4.2v - 5%/cell to optimize battery capacity. when supplying the load and battery charger simultaneously, the input current limit for the ac adapter is programmable to within 3% accuracy to avoid overloading the ac adapter, and to allow the system to make efficient use of available adapter power for charging. it also has a wide range of programmable charging current. the isl6252, isl6252a provides outputs that are used to monitor the current drawn from the ac adapter, and monitor for the presence of an ac adapter. the isl6252, isl6252a automatically transitions from regulating current mode to regulating voltage mode. features ? 0.5% charge voltage accuracy (-10c to +100c) ? 3% accurate input current limit ? 3% accurate battery charge current limit ? 25% accurate battery trickle charge current limit ? programmable charge current limit, adapter current limit and charge voltage ? fixed 300khz pwm synchronous buck controller with diode emulation at light load ? overvoltage protection ? output for current dr awn from ac adapter ? ac adapter present indicator ? fast input current limit response ? input voltage range 7v to 25v ? support 2-, 3- and 4-cells battery pack ? up to 17.64v battery-voltage set point ? thermal shutdown ? less than 10a battery leakage current ? supports pulse charging ? pb-free (rohs compliant) applications ? notebook, desknote and sub-notebook computers ? personal digital assistant ordering information part number (notes 1, 2, 3) part marking temp range (c) package (pb-free) pkg. dwg. # isl6252hrz isl 6252hrz -10 to +100 28 ld 5x5 qfn l28.5x5 ISL6252HAZ isl 6252haz -10 to +100 24 ld qsop m24.15 isl6252ahrz isl6252 ahrz -10 to +100 28 ld 5x5 qfn l28.5x5 isl6252ahaz isl6252 ahaz -10 to +100 24 ld qsop m24.15 notes: 1. please refer to tb347 for details on reel specifications. 2. these intersil pb-free plastic packaged products employ special pb-free material se ts, molding compounds/die attach materials, and 100% matte tin plate plus anneal (e3 termination finish, which is rohs compliant and compatible with both sn pb and pb-free soldering operations). intersil pb-free products are msl classified at pb-free peak reflow te mperatures that meet or exceed the pb-free requirements of ipc/jedec j std- 020. 3. for moisture sensitivity level (msl), please see device information page for isl6252 , isl6252a . for more information on msl pl ease see techbrief tb363 . data sheet august 25, 2010 caution: these devices are sensitive to electrostatic discharge; follow proper ic handling procedures. 1-888-intersil or 1-888-468-3774 | intersil (and design) is a registered trademark of intersil americas inc. copyright intersil americas inc. 2007, 2008, 2010. all rights reserved all other trademarks mentioned are the property of their respective owners.
2 fn6498.3 august 25, 2010 pinouts isl6252, isl6252a (28 ld qfn) top view isl6252, isl6252a (24 ld qsop) top view 1 2 3 4 5 6 7 21 20 19 18 17 16 15 28 27 26 25 24 23 22 8 9 10 11 12 13 14 en cells icomp vcomp icm vref chlim aclim pgnd lgate vddp boot csop phase ugate acset dcin acprn cson vadj gnd csin csip na na na vdd na dcin 124 vdd 223 acprn acset 322 cson 421 csop en 520 csin cells 619 csip icomp 718 vcomp 817 icm 916 phase vref 10 15 ugate chlim 11 14 boot aclim 12 13 vddp vadj lgate gnd pgnd isl6252, isl6252a
3 fn6498.3 august 25, 2010 figure 1. functional block diagram + - 514k 32k dcin vdd boot ugate phase en gnd fb cson csop chlim aclim icomp vcomp vadj cells vref icm csip csin +- + - ca1 x19.9 + - ca2 x19.9 1.26v acset acprn ldo regulator vddp lgate pgnd pwm 300khz ramp + - 1.065v 16k 48k 288k + - gm1 reference voltage selector vdd 514k vref 152k 152k vref 2.1v min current buffer gm3 adapter current limit set + - min voltage buffer + - gm2 -0.25 isl6252, isl6252a
4 fn6498.3 august 25, 2010 figure 2. isl6252, isl6252a typical application circuit with fixed charging parameters csip csin boot ugate phase lgate pgnd csop cson cells icm gnd dcin acset vddp vdd acprn icomp vcomp vadj en aclim vref chlim q1 l 4.7h f c10 r1 ac adapter r5 100k r8 130k 1% r9 10.2k 1% c4 0.1f 1f isl6252 isl floating 4.2v/cell r10 4.7 3.3v bat+ bat- vdd 4 cells d1 d2 vddp vref trickle charge r12 20k 1% q6 130k 1% r13 1.87k 1% 2.6a charge limit 253ma trickle charge charge enable c11 3300pf r7: 100 csip csin boot ugate phase lgate pgnd csop cson cells icm gnd dcin acset vddp vdd acprn icomp vcomp vadj en aclim vref chlim q2 l 1% 0.1 c9 1 isl6252 is6252 r10 c7 1f bat- vdd d1 optional d2 c5 c6 r6 to host controller r11 c1:10 battery pack csip csin boot ugate phase lgate pgnd csop cson cells icm gnd dcin acset vddp vdd acprn icomp vcomp vadj en aclim vref chlim q1 l f c10 20m 100k c4 0.1 1 isl6252 isl6252 r10 4.7 3.3v bat- vdd 4 cells d1 d2 r12 20k 1% r13 2.6a charge limit csip csin boot ugate phase lgate pgnd csop cson cells icm gnd dcin acset vddp vdd acprn icomp vcomp vadj en aclim vref chlim q2 l 0.1 1 isl6252 r10 c7 bat- vdd d1 d2 r11 c1:10 4.7k 10nf 6.8nf isl6252a 22f system load r2 20m r21 c2 0.1f 0.1 2.2 c2 0.1 0.1 r22 22 c3 c3 r11 22 r12 22 0.047f c8 0.1f vdd r23 10k d5 1n914 d3 d4 isl6252, isl6252a
5 fn6498.3 august 25, 2010 figure 3. isl6252, isl6252a typical application circuit with p control csip csin boot ugate phase lgate pgnd csop cson cells vadj gnd dcin acset vddp vdd acprn chlim en icm aclim vref icomp vcomp q1 q2 c1:10f system load r1 adapter r2 20m r21 r6 r5 100k r8 130k 1% r9 10.2k 1% c2 0.1f c4 0.1f c3 c5 10nf c6 6.8nf c9 1f d3 isl6252 isl6252 c7 f r10 4.7 bat+ scl sdl temp bat- scl sdl a/d input gnd vcc d/a output output digital input host avdd/vref gnd floating 4.2v/cell 5.15a input current limit r11, r12 r13: 10k a/d input 100k r7: 100 c11 csip csin boot ugate phase lgate pgnd csop cson cells vadj gnd dcin acset vddp vdd acprn chlim en icm aclim vref icomp vcomp r1 r6 4.7k 1% 0.1 0.1 1 gnd battery pack isl6252 isl 3300pf vddp d2 d1 optional csin ugate phase lgate pgnd csop cson cells vadj gnd dcin acset vddp vdd acprn chlim en icm aclim vref icomp vcomp q2 system load r1 2.2 c2 0.1 c4 0.1 c3 c6 c9 c7 r10 gnd 3-cells r16 r7: c11 csip boot r1 20m 0.1 0.1 1 1 gnd isl6252 3300pf vddp d2 d1 isl6252a l 4.7h c10 22f r22 22 r11 22 r12 22 0.047f c8 0.1f vdd r23 10k d5 1n914 cson d4 isl6252, isl6252a
6 fn6498.3 august 25, 2010 absolute maximum rati ngs thermal information acset to gnd (note 4) . . . . . . . . . . . . . . . . . . -0.3v to vdd +0.3v dcin, csip, cson to gnd. . . . . . . . . . . . . . . . . . . . . -0.3v to +28v csip-csin, csop-cson . . . . . . . . . . . . . . . . . . . . . -0.3v to +0.3v phase to gnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -7v to 30v boot to gnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3v to +35v boot to vddp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -2v to 28v aclim, acprn, chlim, vdd to gnd . . . . . . . . . . . . . . -0.3v to 7v boot-phase, vddp-pgnd . . . . . . . . . . . . . . . . . . . . . -0.3v to 7v icm, icomp, vcomp to gnd. . . . . . . . . . . . . . -0.3v to vdd +0.3v vref, cells to gnd . . . . . . . . . . . . . . . . . . . . -0.3v to vdd +0.3v en, vadj, pgnd to gnd . . . . . . . . . . . . . . . . . -0.3v to vdd +0.3v ugate. . . . . . . . . . . . . . . . . . . . . . . . phase -0.3v to boot +0.3v lgate . . . . . . . . . . . . . . . . . . . . . . . . . pgnd -0.3v to vddp +0.3v thermal resistance ja (c/w) jc (c/w) qfn package (notes 5, 6). . . . . . . . . . 39 9.5 qsop package (note 5) . . . . . . . . . . . 80 n/a junction temperature range. . . . . . . . . . . . . . . . . .-10c to +150c operating temperature range . . . . . . . . . . . . . . . .-10c to +100c storage temperature . . . . . . . . . . . . . . . . . . . . . . . .-65c to +150c pb-free reflow profile . . . . . . . . . . . . . . . . . . . . . . . . . .see link below http://www.intersil.com/pbfree/pb-freereflow.asp caution: do not operate at or near the maximum ratings listed fo r extended periods of time. exposure to such conditions may adv ersely impact product reliability and result in failures not covered by warranty. notes: 4. acset may be operated 1v below gnd if the current through acset is limited to less than 1ma. 5. ja is measured in free air with the component mounted on a high effe ctive thermal conductivity test board with ?direct attach? fea tures. see tech brief tb379. 6. for jc , the ?case temp? location is the center of the exposed metal pad on the package underside. electrical specifications dcin = csip = csin = 18v, csop = cson = 12v, acset = 1.5v, aclim = vref, vadj = floating, en = vdd = 5v, boot-phase = 5.0v, gnd = pgnd = 0v, c vdd =1f, i vdd =0ma, t a = -10c to +100c, t j +125c, unless otherwise noted. boldface limits apply over the operating temperature range, -10c to +100c. parameter test conditions min (note 8) typ max (note 8) units supply and bias regulator dcin input voltage range 725 v dcin quiescent current en = vdd or gnd, 7v dcin 25v 1.4 3 ma battery leakage current (note 6) dcin = 0, no load 3 10 a vdd output voltage/regulation 7v dcin 25v, 0 i vdd 30ma 4.925 5.075 5.225 v vdd undervoltage lockout trip point vdd rising 4.0 4.4 4.6 v hysteresis 200 250 400 mv reference output voltage vref 0 i vref 300a 2.365 2.39 2.415 v battery charge voltage accuracy cson = 16.8v, cells = vdd, vadj = float -0.5 0.5 % cson = 12.6v, cells = gnd, vadj = float -0.5 0.5 % cson = 8.4v, cells = float, vadj = float -0.5 0.5 % cson = 17.64v, cells = vdd, vadj = vref -0.5 0.5 % cson = 13.23v, cells = gnd, vadj = vref -0.5 0.5 % cson = 8.82v, cells = float, vadj = vref -0.5 0.5 % cson = 15.96v, cells = vdd, vadj = gnd -0.5 0.5 % cson = 11.97v, cells = gnd, vadj = gnd -0.5 0.5 % cson = 7.98v, cells = float, vadj = gnd -0.5 0.5 % trip points acset threshold 1.24 1.26 1.28 v acset input bias current hysteresis 2.4 3.4 4.4 a acset input bias current acset 1.26v 2.4 3.4 4.4 a acset input bias current acset < 1.26v -1 0 1 a isl6252, isl6252a
7 fn6498.3 august 25, 2010 oscillator frequency 245 300 355 khz pwm ramp voltage (peak-peak) csip = 18v 1.6 v csip = 11v 1 v synchronous buck regulator maximum duty cycle 97 99 99.6 % ugate pull-up resistance boot-phase = 5v, 500ma source current 1.8 3.0 ugate source current boot-phase = 5v, boot-ugate = 2.5v 1.0 a ugate pull-down resistance boot-phase = 5v, 500ma sink current 1.0 1.8 ugate sink current boot-phase = 5v, ugate-phase = 2.5v 1.8 a lgate pull-up resistance vddp-pgnd = 5v, 500ma source current 1.8 3.0 lgate source current vddp-pgnd = 5v, vddp-lgate = 2.5v 1.0 a lgate pull-down resistance vddp-pgnd = 5v, 500ma sink current 1.0 1.8 lgate sink current vddp-pgnd = 5v, lgate = 2.5v 1.8 a dead time falling ugate to rising lgate or falling lgate to rising ugate 10 30 ns charging current sensing amplifier input common-mode range 018 v input bias current at csop 5 < csop < 18v 0.25 2 a input bias current at cson 5 < cson < 18v 75 100 a chlim input voltage range 03.6 v isl6252 csop to cson full-scale current sense voltage isl6252: chlim = 3.3v 160 165 170 mv isl6252: chlim = 2.0v 95 100 105 mv isl6252: chlim = 0.2v 5.0 10 15.0 mv isl6252a csop to cson full-scale current sense voltage isl6252a: chlim = 3.3v 161.7 165 168.3 mv isl6252a: chlim = 2.0v 97 100 103 mv isl6252a: chlim = 0.2v 7.5 10 12.5 mv isl6252 csop to cson full-scale current sense voltage formula charge current limit mode 0.2v < chlim < 3.3v chlim*50 - 5 chlim*50 + 5 mv isl6252a csop to cson full-scale current sense voltage formula charge current limit mode 0.2v < chlim < 3.3v chlim*49.72 - 2.4 chlim*50.28 + 2.4 mv chlim input bias current chlim = gnd or 3.3v, dcin = 0v -1 1 a chlim power-down mode threshold voltage chlim rising 80 88 95 mv chlim power-down mode hysteresis voltage 15 25 40 mv adapter current sensing amplifier input common-mode range 7 25 v input bias current at csip and csin combined csip = csin = 25v 100 130 a input bias current at csin 0 < csin < dcin 0.10 a electrical specifications dcin = csip = csin = 18v, csop = cson = 12v, acset = 1.5v, aclim = vref, vadj = floating, en = vdd = 5v, boot-phase = 5.0v, gnd = pgnd = 0v, c vdd =1f, i vdd =0ma, t a = -10c to +100c, t j +125c, unless otherwise noted. boldface limits apply over the operating temperature range, -10c to +100c. (continued) parameter test conditions min (note 8) typ max (note 8) units isl6252, isl6252a
8 fn6498.3 august 25, 2010 adapter current limit threshold csip to csin full-scale current sense voltage aclim = vref 97 100 103 mv aclim = float 72 75 78 mv aclim = gnd 47 50 53 mv aclim input bias current aclim = vref 10 16 20 a aclim = gnd -20 -16 -10 a voltage regulation error amplifier error amplifier transconductance from cson to vcomp cells = vdd 30 a/v current regulation error amplifier charging current error amplifier transconductance 50 a/v adapter current error amplifier transconductance 50 a/v battery cell selector cells input voltage for 4-cell select 4.3 v cells input voltage for 3-cell select 2 v cells input voltage for 2-cell select 2.1 4.2 v logic interface en input voltage range 0vdd v en threshold voltage rising 1.030 1.06 1.100 v falling 0.985 1.000 1.025 v hysteresis 30 60 90 mv en input bias current en = 2.5v 1.8 2.0 2.2 a acprn sink current acprn = 0.4v 3 8 11 ma acprn leakage current acprn = 5v -0.5 0.5 a icm output accuracy (v icm = 19.9 x (v csip - v csin )) csip-csin = 100mv -3 0 +3 % csip-csin = 75mv -4 0 +4 % csip-csin = 50mv -5 0 +5 % thermal shutdown temperature 150 c thermal shutdown temperature hysteresis 25 c note: 7. this is the sum of currents in these pins (csip, csin, boot, ugate, phase, csop, cson) all tied to 16.8v. no current in pins en, acset, vadj, cells, aclim, chlim. 8. parameters with min and/or max limits are 100% tested at +25c, unless otherwise specif ied. temperature limits are established by characterization and are not production tested. electrical specifications dcin = csip = csin = 18v, csop = cson = 12v, acset = 1.5v, aclim = vref, vadj = floating, en = vdd = 5v, boot-phase = 5.0v, gnd = pgnd = 0v, c vdd =1f, i vdd =0ma, t a = -10c to +100c, t j +125c, unless otherwise noted. boldface limits apply over the operating temperature range, -10c to +100c. (continued) parameter test conditions min (note 8) typ max (note 8) units isl6252, isl6252a
9 fn6498.3 august 25, 2010 typical operating performance dcin = 20v, 4s2p li-battery, t a = +25c, unless otherwise noted. figure 4. vdd load regulation figure 5. vref load regulation figure 6. accuracy vs ac adapter current figure 7. system efficiency vs charge current figure 8. ac and dc adapter detection figure 9. load transient response vdd load regulation accuracy (%) 0.6 0.3 0.0 -0.3 -0.6 15 0 5 10 20 40 load current (ma) vref load regulation accuracy (%) 0.10 0.08 0.06 0.04 0.00 0 100 200 300 400 0.02 load current (a) 0 1 2 3 4 5 6 7 8 9 10 10 20 30 40 50 60 70 80 90 100 | accuracy | (%) csip-csin (mv) 0 load current (a) efficiency (%) 100 96 92 88 84 80 76 1.5 0 0.5 1.0 2.0 2.5 3.0 3.5 4.0 vcson = 16.8v vcson = 8.4v 2 cells vcson = 12.6v 3 cells 4 cells dcin 10v/div acset 1v/div dcset 1v/div dcprn 5v/div acprn 5v/div dcin 10v/div acset 1v/div dcset 1v/div dcprn 5v/div acprn 5v/div load current 5a/div a dapter current 5a/div charge current 2a/div battery voltage 2v/div load step: 0-4a charge current: 3a a c adapter current limit: 5.15a load step: 0a to 4a charge current: 3a ac adapter current limit: 5.15a isl6252, isl6252a
10 fn6498.3 august 25, 2010 figure 10. charge enable and shutdown figure 11. battery insertion and removal figure 12. switching waveforms at diode emulat ion figure 13. switching waveforms in cc mode figure 14. ac adapter removal figure 15. ac adapter insertion typical operating performance dcin = 20v, 4s2p li-battery, t a = +25c, unless otherwise noted. (continued) cson 5v/div en 5v/div inductor current 2a/div charge current 2a/div cson 5v/div en 5v/div inductor current 2a/div charge current 2a/div inductor current 2a/div cson 10v/div vcomp icomp battery insertion battery removal vcomp 2v/div icomp 2v/div inductor current 2a/div cson 10v/div vcomp icomp battery insertion battery removal vcomp 2v/div icomp 2v/div battery insertion battery removal vcomp icomp phase 10v/div inductor current 1a/div ugate 5v/div chlim=0.2v cson=8v phase 10v/div inductor current 1a/div ugate 5v/div phase 10v/div inductor current 1a/div ugate 5v/div chlim=0.2v cson=8v chlim = 0.2v cson = 8v phase 10v/div lgate 2v/div ugate 2v/div phase 10v/div lgate 2v/div ugate 2v/div inductor current 2a/div bgate-csip 2v/div system bus voltage 10v/div sgate-csip 2v/div adapter removal inductor current 2a/div bgate-csip 2v/div system bus voltage 10v/div sgate-csip 2v/div inductor current 2a/div bgate-csip 2v/div system bus voltage 10v/div sgate-csip 2v/div adapter removal adapter removal inductor current 2a/div sgate-csip 2v/div system bus voltage 10v/div bgate-csip 2v/div adapter insertion inductor current 2a/div sgate-csip 2v/div system bus voltage 10v/div bgate-csip 2v/div inductor current 2a/div sgate-csip 2v/div system bus voltage 10v/div bgate-csip 2v/div adapter insertion adapter insertion isl6252, isl6252a
11 fn6498.3 august 25, 2010 functional pin descriptions boot connect boot to a 0.1f ce ramic capacitor to phase pin and connect to the cathode of the bootstrap schottky diode. ugate ugate is the high side mosfet gate drive output. lgate lgate is the low side mosfet gate drive output; swing between 0v and vddp. phase the phase connection pin connects to the high side mosfet source, output inductor, and low side mosfet drain. csop/cson csop/cson is the battery charging current sensing positive/negative input. the di fferential voltage across csop and cson is used to sense the battery charging current, and is compared with the charging current limit threshold to regulate the charging current. the cson pin is also used as the battery feedback voltage to perform voltage regulation. csip/csin csip/csin is the ac adapter current sensing positive/negative input. the differential voltage across csip and csin is used to sense the ac adapter current, and is compared with the ac adapter current limit to regulate the ac adapter current. gnd gnd is an analog ground. dcin the dcin pin is the input of the internal 5v ldo. connect it to the ac adapter output. connect a 0.1f ceramic capacitor from dcin to cson. acset acset is an ac adapter detection input. connect to a resistor divider from the ac adapter output. acprn open-drain output signals ac adapter is present. acprn pulls low when acset is higher than 1.26v; and pulled high when acset is lower than 1.26v. en en is the charge enable input. connecting en to high enables the charge control function, connecting en to low disables charging functions. use with a thermistor to detect a hot battery and suspend charging. icm icm is the adapter current ou tput. the output of this pin produces a voltage proportion al to the adapter current. pgnd pgnd is the power ground. connect pgnd to the source of the low side mosfet. vdd vdd is an internal ldo output to supply ic analog circuit. connect a 1f ceramic capacitor to ground. vddp vddp is the supply voltage for the low-side mosfet gate driver. connect a 4.7 resistor to vdd and a 1f ceramic capacitor to power ground. icomp icomp is a current loop error amplifier output. vcomp vcomp is a voltage loop amplifier output. cells this pin is used to select the battery voltage. cells = vdd for a 4s battery pack, cells = gnd for a 3s battery pack, cells = float for a 2s battery pack. figure 16. trickle to full-scale charging typical operating performance dcin = 20v, 4s2p li-battery, t a = +25c, unless otherwise noted. (continued) chlim 1v/div charge current 1a/div isl6252, isl6252a
12 fn6498.3 august 25, 2010 vadj vadj adjusts battery regulation voltage. vadj = vref for 4.2v + 5%/cell; vadj = floating for 4.2v/cell; vadj = gnd for 4.2v - 5%/cell. connect to a resistor divider to program the desired battery cell voltage between 4.2v - 5% and 4.2v + 5%. chlim chlim is the battery charge current limit set pin. chlim input voltage range is 0.1v to 3.6v. when chlim = 3.3v, the set point for csop to cson is 165mv. the charger shuts down if chlim is forced below 88mv. aclim aclim is the adapter current limit set pin. aclim = vref for 100mv, aclim = floating for 75mv, and aclim = gnd for 50mv. connect a resistor divider to program the adapter current limit threshold between 50mv and 100mv. vref vref is a 2.39v reference output pin. it is internally compensated. do not connect a decoupling capacitor. theory of operation introduction unless otherwise noted, all descriptions of isl6252 refer to both isl6252 and isl6252a. the isl6252 includes all of the functions necessary to charge 2- to 4-cell li-ion and li-polymer batteries. a high efficiency synchronous buck converter is used to control the charging voltage and charging current up to 10a. the isl6252 has input current limiting and analog inputs for setting the charge current and charge voltage; chlim inputs are used to control charge current and vadj inputs are used to control charge voltage. the isl6252 charges the batte ry with constant charge current, set by chlim input, until the battery voltage rises up to a programmed charge voltage se t by vadj input; then the charger begins to operate at a constant voltage charge mode. the charger also drives an adapter isolation p-channel mosfet to efficiently switch in the adapter supply. isl6252 is a complete power source selection controller for single battery systems and also aircraft power applications. it drives a battery selector p-channel mosfet to efficiently select between a single battery and the adapter. it controls the battery discharging mosfet and switches to the battery when the ac adapter is remo ved or switches to the ac adapter when the ac adapter is inserted for single battery system. the en input allows shutdown of the charger through a command from a micro-controller. it also uses en to safely shutdown the charger when the battery is in extremely hot conditions. the amount of adapter current is reported on the icm output. figure 1 shows the ?ic functional block diagram? on page 3. the synchronous buck converte r uses external n-channel mosfets to convert the input voltage to the required charging current and charging voltage. figure 2 shows the isl6252 typical application ci rcuit with charging current and charging voltage fixed at specific values. the typical application circuit shown in figure 3 shows the isl6252 typical application circuit, whic h uses a micro-controller to adjust the charging current set by chlim input for aircraft power applications. the voltage at chlim and the value of r 1 sets the charging current. t he dc/dc conver ter generates the control signals to drive tw o external n-channel mosfets to regulate the voltage and current set by the aclim, chlim, vadj and cells inputs. the isl6252 features a voltage regulation loop (vcomp) and two current regulation loops (icomp). the vcomp voltage regulation loop monitors cson to ensure that its voltage never exceeds the voltage and regulates the battery charge voltage set by vadj. the icomp current regulation loops regulate the battery charging current delivered to the battery to ensure that it never exceeds the charging current limit set by chlim; and the icomp current regulation loops also regulate the input current drawn from the ac adapter to ensure that it never exceeds the input current limit set by aclim, and to prevent a syst em crash and ac adapter overload. pwm c o ntrol the isl6252 employs a fixed frequency pwm current mode control architecture with a feed-forward function. the feed-forward function maintains a constant modulator gain of 11 to achieve fast line regulation as the buck input voltage changes. when the battery charge voltage approaches the input voltage, the dc/dc conv erter operates in dropout mode, where there is a timer to prevent the frequency from dropping into the audible frequency range. it can achieve duty cycle of up to 99.6%. to prevent boosting of the syst em bus voltage, the battery charger operates in standard-buck mode when csop-cson drops below 4.25mv. once in standard-buck mode, hysteresis does not allow synchronous operation of the dc/dc converter until csop-cson rises above 12.5mv. an adaptive gate drive scheme is used to control the dead time between two switches. the dead time control circuit monitors the lgate output and prevents the upper side mosfet from turning on until lgate is fully off, preventing cross-conduction and shoot-through. in order for the dead time circuit to work properly, there must be a low resistance, low inductance path from the lgate driver to mosfet gate, and from the source of mosfet to pgnd. the external schottky diode is between the vddp pin and boot pin to keep the bootstrap capacitor charged. isl6252, isl6252a
13 fn6498.3 august 25, 2010 setting the battery regulation voltage the isl6252 uses a high-accuracy trimmed band-gap voltage reference to regulate the battery charging voltage. the vadj input adjusts the charger output voltage, and the vadj control voltage can vary from 0 to vref, providing a 10% adjustment range (from 4.2v - 5% to 4.2v + 5%) on cson regulation voltage. an overall voltage accuracy of better than 0.5% is achieved. the per-cell battery termination voltage is a function of the battery chemistry (consult the battery manufacturers to determine this voltage): ? float vadj to set the battery voltage v cson =4.2v number of the cells ? connect vadj to vref to set 4.41v number of cells ? connect vadj to ground to set 3.99v number of cells so, the maximum battery voltage of 17.6v can be achieved. note that other battery charge voltages can be set by connecting a resistor divider from vref to ground. the resistor divider should be sized to draw no more than 100a from vref; or connect a low impedance voltage source like the d/a converter in the micro-contro ller. the programmed battery voltage per cell can be determined by equation 1: an external resistor divider from vref sets the voltage at vadj according to equation 2: to minimize accuracy loss due to interaction with vadj's internal resistor divider, ensu re the ac resistance looking back into the external resistor divider is less than 25k. connect cells as shown in table 1 to charge 2, 3 or 4 li+ cells. when charging other cell chemistries, use cells to select an output voltage range for the charger. the internal error amplifier gm1 maintains voltage regulation. the voltage error amplifier is compensated at vcomp. the component values shown in figure 3 provide suitable performance for most applications. individual compensat ion of the voltage regulation and current-regulation loops allows for optimal compensation. setting the battery charge current limit the chlim input sets the maximum charging current. the current set by the current sense-resistor connects between csop and cson. the full-scale differential voltage between csop and cson is 165mv for chlim = 3.3v, so the maximum charging current is 4.125a for a 40m sensing resistor. other battery charge current-sense threshold values can be set by connecting a resistor divider from vref or 3.3v to ground, or by connecting a low impedance voltage source like a d/a converter in the micro-controller. unlike vadj and aclim, chlim does not have an internal resistor divider network. the charge current limit threshold is given by equation 3: to set the trickle charge current for the dumb charger, an a/d output controlled by the micr o-controller is connected to chlim pin. the trickle charge current is determined by equation 4: when the chlim voltage is below 88mv (typical), it will disable the battery charge . when choosing the current sensing resistor, note that th e voltage drop across the sensing resistor causes further power dissipation, reducing efficiency. however, adjusting chlim voltage to reduce the voltage across the current sense resistor r 1 will degrade accuracy due to the smaller signal to the input of the current sense amplifier. there is a trade-off between accuracy and power dissipation. a low pass filter is recommended to eliminate switching noise. connect the resistor to the csop pin instead of the cson pin, as the csop pin has lower bias current and less influence on current-sense accuracy and voltage regulation accuracy. charge current limit accuracy the ?electrical specifications? table on page 6 gives minimum and maximum values for the csop-cson voltage resulting from ic variations at 3 different chlim voltages (csop-cson full-scale current sense voltage on page 7). it also gives formulae for calculating the minimum and maximum csop-cson voltage at any chlim voltage. equation 5 shows the formula for the max full scale csop-cson voltage (in mv) for the isl6252a: table 1. cell number programming cells cell number vdd 4 gnd 3 float 2 v cell 0.175 v vadj ? 3.99v + = (eq. 1) v vadj vref r bot_vadj 514k || r top _vadj 514k || r bot_vadj 514k || + ---------------------------------------------------------------------------------------------------------------- - = (eq. 2) i chg 165mv r 1 ------------------- ?? ?? v chlim 3.3v --------------------- - ?? ?? = (eq. 3) i chg 165mv r 1 ------------------- ?? ?? v chlim trickle , 3.3v --------------------------------------- - ?? ?? = (eq. 4) isl6252a csop cson ? () max chlim 50.28 2.4 + ? = csop cson ? () min chlim 49.72 2.4 ? ? = (eq. 5) isl6252, isl6252a
14 fn6498.3 august 25, 2010 equation 5 shows the formula for the max full scale csop-cson voltage (in mv) for the isl6252: with chlim = 1.5v, the maximum csop-cson voltage is 78mv and the minimum csop-cson voltage is 72mv. when isl6252a is in charge current limiting mode, the maximum charge current is the maximum csop-cson voltage divided by the minimum sense resistor. this can be calculated for isl6252a with equation 7: maximum charge current can be calculated for isl6252 with equation 8: with chlim = 0.7v and r 1 = 0.02 , 1%: setting the input current limit the total input current from an ac adapter, or other dc source, is a function of the system supply current and the battery-charging current. the in put current regulator limits the input current by reducing the charging current, when the input current exceeds the input current limit set point. system current normally fluctuat es as portions of the system are powered up or down. without input current regulation, the source must be able to supply the maximum system current and the maximum charger input current simultaneously. by using the input current limiter, the current capability of the ac adapter can be lowered, reducing system cost. the isl6252 limits the battery charge current when the input current-limit threshold is exceeded, ensuring the battery charger does not load down t he ac adapter voltage. this constant input current regulation allows the adapter to fully power the system and prev ent the ac adapter from overloading and cras hing the system bus. an internal amplifier gm3 compares the voltage between csip and csin to the input current limit threshold voltage set by aclim. connect aclim to ref, float and gnd for the full-scale input current limit threshold voltage of 100mv, 75mv and 50mv, respectively, or use a resistor divider from vref to ground to set the input current limit as equation 10: an external resistor divider from vref sets the voltage at aclim according to equation 11: where r bot_aclim and r top_aclim are external resistors at aclim. to minimize accuracy loss due to interaction with aclim's internal resistor divider, ensure the ac resistance looking back into the resistor divider is less than 25k. when choosing the current sens e resistor, note that the voltage drop across this resistor causes further power dissipation, reducing efficien cy. the ac adapter current sense accuracy is very important. use a 1% tolerance current-sense resistor. the highest accuracy of 3% is achieved with 100mv current-sense threshold voltage for aclim = vref, but it has the highest power dissipation. for example, it has 400mw power dissipation for rated 4a ac adapter and 1 sensing resistor may have to be used. 4% and 6% accuracy can be achieved with 75mv and 50mv current-sense threshold voltage for aclim = floating and aclim = gnd, respectively. a low pass filter is suggested to eliminate the switching noise. connect the resistor to csin pin instead of csip pin because csin pin has lower bias current and less influence on the current-sense accuracy. ac adapter detection connect the ac adapter voltage through a resistor divider to acset to detect when ac power is available, as shown in figure 2. acprn is an open-dr ain output and is high when acset is less than v th,rise , and active low when acset is above v th,fall . v th,rise and v th,fall are given by equation 12 and equation 13: where: ?i hys is the acset input bias current hysteresis, and ?v acset = 1.24v (min), 1.26v (t yp) and 1.28v (max). the hysteresis is i hys r 8 , where i hys = 2.2a (min), 3.4a (typ) and 4.4a (max). isl6252 max csop cson ? () chlim 50 5 + ? = min csop cson ? () chlim 50 5 ? ? = (eq. 6) isl6252a i chg max , chlim 50.28 2.4 + ? () r 1min ? = i chg min , chlim 49.72 2.4 ? ? () r 1max ? = (eq. 7) isl6252 i chg max , chlim 50 5 + ? () r 1min ? = i chg min , chlim 50 5 ? ? () r 1max ? = (eq. 8) isl6252a i chg max , 1.5v 50.28 2.4 + ? () 0.0198 3930ma = ? = i chg min , 1.5v 49.72 2.4 ? ? () 0.0202 3573ma = ? = (eq. 9) i input 1 r 2 ------ - 0.05 vref ---------------- - v aclim 0.05 + ? ?? ?? ? = (eq. 10) v aclim vref r bot aclim , 152k || r top aclim , 152k || r bot aclim , 152k || + ----------------------------------------------------------------------------------------------------------------------- - ?? ?? ?? ? = (eq. 11) v th rise , r 8 r 9 ------ - 1 + ?? ?? ?? v acset ? = (eq. 12) v th fall , r 8 r 9 ------ - 1 + ?? ?? ?? v acset i hys r 8 ? ? ? = (eq. 13) isl6252, isl6252a
15 fn6498.3 august 25, 2010 current measurement use icm to monitor the input current being sensed across csip and csin. the output volt age range is 0v to 2.5v. the voltage of icm is proportional to the voltage drop across csip and csin, and is given by equation 14: where i input is the dc current drawn from the ac adapter. icm has 3% accuracy. it is recommended to have an rc filter at the icm output for minimizing the switching noise. ldo regulator vdd provides a 5.0v supply voltage from the internal ldo regulator from dcin and can deliver up to 30ma of current. the mosfet drivers are powered by vddp, which must be connected to vddp as shown in figure 2. vddp connects to vdd through an external low pass filter. bypass vddp and vdd with a 1f capacitor. shutdown the isl6252 features a low-pow er shutdown mode. driving en low shuts down the isl6252. in shutdown, the dc/dc converter is disabled, and vcomp and icomp are pulled to ground. the icm, acprn output continue to function. en can be driven by a thermistor to allow automatic shutdown of the isl6252 when the battery pack is hot. often a ntc thermistor is included inside the battery pack to measure its temperature. when connected to the charger, the thermistor forms a voltage divider with a resistive pull-up to the vref. the threshold voltage of en is 1.0v with 60mv hysteresis. the thermistor can be selected to have a resistance vs temperature characteristic that abruptly decreases above a critical te mperature. this arrangement automatically shuts down the isl6252 when the battery pack is above a critical temperature. another method for inhibiting charging is to force chlim below 85mv (typ). short circuit protection and 0v battery charging since the battery charger will regulate the charge current to the limit set by chlim, it aut omatically has short circuit protection and is able to provide the charge current to wake up an extremely discharged battery. over-temperature protection if the die temp exceeds +150c, it stops charging. once the die temp drops below +125c, charging will start up again. overvoltage protection isl6252 has an overvoltage protec tion circuit that limits the output voltage when the battery is removed or disconnected by a pulse charging circuit. if cson exceeds the output voltage set point by more than v ovp an internal comparator pulls vcomp down and turns off both upper and lower fets of the buck, as in figure 17. the trip point for overvoltage protection is always above t he nominal output voltage and can be calculated from equation 15: for example, if the cells pin is connected to ground (n cells = 3) and v adj is floating (v adj = 1.195v) then v out,nom = 12.6v and v ovp = 12.693v or v out,nom +93mv. there is a delay of approximately 400nsec between v out exceeding the ovp trip point and pulling vcomp, lgate and ugate low. during normal operation with cells installed, the cson pin voltage will be the cell stack voltage. when en is low and the cells are removed, this voltage may drop below 100mv. due to non-linearities in the ovp co mparator at this low input level, the vcomp pin may be held low even after en is commanded high. if regulation is required in the absence of cells then a series resistor and diode need to be installed which inject current into the cson pin from the v dd pin. see r23 and d5 in figure 3. this will maintain the cson pin voltage well within its linear range in the absence of cells, and will be effectively out of the circuit when the diode is reversed biased by the cell stack. resistor values from 10k to 100k have been found to be effective. application information the following battery charger design refers to the typical application circuit in figure 2, where typical battery configuration of 4s2p is used. this section describes how to select the external components including the inductor, input and output capacitors, switching mosfets, and current sensing resistors. icm 19.9 i input r 2 ? ? = (eq. 14) v ovp v out nom , n cells 42.2mv 22.2mv v adj 2.39v --------------- - ? ?? ?? + = (eq. 15) figure 17. overvoltage protection in isl6252 battery removal when v out exceeds the ovp threshold vcomp is pulled low and fets turn off vcomp icomp v out phase current flows in the lower fet body diode until inductor current reaches zero isl6252, isl6252a
16 fn6498.3 august 25, 2010 inductor selection the inductor selection has trade-offs between cost, size, crossover frequency and efficiency. for example, the lower the inductance, the smaller the size, but ripple current is higher. this also results in higher ac losses in the magnetic core and the windings, which decrease the system efficiency. on the other hand, the higher inductance results in lower ripple current and smaller output filter capacitors, but it has higher dcr (dc resistance of the inductor) loss, lower saturation current and has slower transient response. so, the practical inductor desi gn is based on the inductor ripple current being 15% to 20% of the maximum operating dc current at maximum input voltage. maximum ripple is at 50% duty cycle or v bat =v in,max /2. the required inductance can be calculated from equation 16: where v in,max and f sw are the maximum input voltage, and switching frequency, respectively. the inductor ripple current i is found from equation 17: where the maximum peak-to-peak ripple current is 30% of the maximum charge current is used. for v in,max = 19v, v bat = 16.8v, i bat,max = 2.6a, and f s = 300khz, the calculated inductance is 8.3h. choosing the closest standard value gives l = 10h. ferrite cores are often the best choice since they are optimized at 300khz to 600khz operation with low core loss. the core must be large enough not to saturate at the peak inductor current ipeak in equation 18: inductor saturation can lead to cascade failures due to very high currents. conservative design limits the peak and rms current in the inductor to less than 90% of the rated saturation current. crossover frequency is heavily dependent on the inductor value. f co should be less than 20% of the switching frequency and a conservative design has f co less than 10% of the switching frequency. the highest f co is in voltage control mode with the ba ttery removed and may be calculated (approximately) from equation 19: output capacitor selection the output capacitor in parallel with the battery is used to absorb the high frequency switching ripple current and smooth the output voltage. the rms value of the output ripple current i rms is given by equation 20: where the duty cycle d is the ratio of the output voltage (battery voltage) over the input voltage for continuous conduction mode which is typical operation for the battery charger. during the battery ch arge period, the output voltage varies from its initial battery voltage to the rated battery voltage. so, the duty cycle change can be in the range of between 0.53 and 0.88 for t he minimum battery voltage of 10v (2.5v/cell) and the maximum battery voltage of 16.8v. the maximum rms value of the output ripple current occurs at the duty cycle of 0.5 and is expressed as equation 21: for v in,max = 19v, vbat = 16.8v, l = 10h, and f s = 300khz, the maximum rms current is 0.19a. a typical 10f ceramic capacitor is a good choice to absorb this current and also has very small size. organic polymer capacitors have high capacitance with small size and have a significant equivalent series resistance (esr). although esr adds to ripple voltage, it also creates a high frequency zero that helps the closed loop operation of the buck regulator. emi considerations usually make it desirable to minimize ripple current in the battery leads. beads may be added in series with the battery pack to increase the battery impedance at 300khz switching frequency. switching ripple current splits between the battery and the output capacitor depending on the esr of the output capacitor and battery impedance. if the esr of the output capacitor is 10m and battery impedance is raised to 2 with a bead, then only 0.5% of the ripple current will flow in the battery. mosfet selection the notebook battery charger synchronous buck converter has the input voltage from the ac adapter output. the maximum ac adapter output voltage does not exceed 25v. therefore, 30v logic mosfet should be used. the high side mosfet must be able to dissipate the conduction losses plus the swit ching losses. for the battery charger application, the input voltage of the synchronous buck converter is equal to the ac adapter output voltage, which is relatively constant. the maximum efficiency is achieved by selecting a high side mosfet that has the conduction losses equal to the switching losses. switching losses in the low-side fet are very small. the choice of low-side fet is a trade-off between conduction losses (r ds(on) ) and cost. a good rule of thumb for the r ds(on) of the low-side fet is 2x the r ds(on) of the high-side fet. l v in max , 4f sw i ripple ?? --------------------------------------------- = (eq. 16) i ripple 0.3 i ? lmax , = (eq. 17) i peak i lmax , 1 2 -- - + i ripple ? = (eq. 18) f co 511r sense ?? 2 l ? ------------------------------------------ - = (eq. 19) i rms v in max , 12lf sw ?? ----------------------------------- d1d ? () ?? = (eq. 20) i rms v in max , 4 12lf sw ??? ----------------------------------------- = (eq. 21) isl6252, isl6252a
17 fn6498.3 august 25, 2010 the lgate gate driver can drive sufficient gate current to switch most mosfets efficient ly. however, some fets may exhibit cross conduction (or shoot through) due to current injected into the drain-to-source parasitic capacitor (c gd ) by the high dv/dt rising edge at the phase node when the high-side mosfet turns on. although lgate sink current (1.8a typical) is more than enough to switch the fet off quickly, voltage drops across parasitic impedances between lgate and the mosfet can allow the gate to rise during the fast rising edge of volt age on the drain. mosfets with low threshold voltage (<1.5v) and low ratio of c gs /c gd (<5) and high gate resistance (>4 ) may be turned on for a few ns by the high dv/dt (rising edge) on their drain. this can be avoided with higher threshold voltage and c gs /c gd ratio. another way to avoid cross conduction is slowing the turn-on speed of the high-side mosfet by connecting a resistor between the boot pin and the boot strap capacitor. for the high-side mosfet, the worst-case conduction losses occur at the minimum input voltage as shown in equation 22: the optimum efficiency occurs when the switching losses equal the conduction losses. however, it is difficult to calculate the switching losses in the high-side mosfet since it must allow for diff icult-to-quantify factors that influence the turn-on and turn-off times. these factors include the mosfet internal gate resistance, gate charge, threshold voltage, stray inductance, pull-up and pull-down resistance of the gate driver. the following switching loss calculation (equation 23) provides a rough estimate. where the following are the peak gate-drive source/sink current of q 1 , respectively: ?q gd : drain-to-gate charge ?q rr : total reverse recovery charge of the body-diode in low-side mosfet ?i lv : inductor valley current ?i lp : inductor peak current ?i g,sink ?i g , source low switching loss requires low drain-to-gate charge q gd . generally, the lower the drain-to-gate charge, the higher the on-resistance. therefore, there is a trade-off between the on-resistance and drain-to-gate charge. good mosfet selection is based on the figure of merit (fom), which is a product of the total gate charge and on-resistance. usually, the smaller the value of fom, the higher the efficiency for the same application. for the low-side mosfet, the worst-case power dissipation occurs at minimum battery voltage and maximum input voltage (equation 24): choose a low-side mosfet th at has the lowest possible on-resistance with a moderate-sized package (like the so-8) and is reasonably priced. the switching losses are not an issue for the low-side mosfet because it operates at zero-voltage-switching. choose a schottky diode in parallel with low-side mosfet q 2 with a forward voltage drop low enough to prevent the low-side mosfet q 2 body-diode from turning on during the dead time. this also reduces the power loss in the high-side mosfet associated with the reverse recovery of the low-side mosfet q 2 body diode. as a general rule, select a diode with dc current rating equal to one-third of the load current. one option is to choose a combined mosfet with the schottky diode in a single package. the integrated packages may work better in practice because there is less stray inductance due to a short connection. this schottky diode is optional and may be removed if efficiency loss can be tolerated. in addition, ensure that the required total gate drive current for the selected mosfets is less than 24ma. so, the total gate charge for the high-side and low-side mosfets is limited by equation 25: where i gate is the total gate drive current and should be less than 24ma. substituting i gate = 24ma and f s = 300khz into equation 25 yields that the total gate charge should be less than 80nc. therefore, t he isl6252 easily drives the battery charge current up to 10a. snubber design isl6252's buck regulator operates in discontinuous current mode (dcm) when the load current is less than half the peak-to-peak current in the inductor. after the low-side fet turns off, the phase voltage rings due to the high impedance with both fets off. this can be seen in figure 9. adding a snubber (resistor in series with a capacitor) from the phase node to ground can greatly reduce the ringing. in some situations a snubber can improve output ripple and regulation. the snubber capacitor should be approximately twice the parasitic capacitance on the phase node. this can be p q1 conduction , v out v in --------------- - i bat 2 r ds on () ?? = (eq. 22) q1 switching , v in i lv f sw q gd i gsource , ------------------------ - ?? ?? ?? 1 2 -- - v in i lp f sw q gd i gk sin , ----------------- ?? ?? ?? q rr v in f sw + + = (eq. 23) p q2 1 v out v in --------------- - ? ?? ?? ?? i bat 2 r ds on () ?? = (eq. 24) q gate 1 gate f sw ------------------ - (eq. 25) isl6252, isl6252a
18 fn6498.3 august 25, 2010 estimated by operating at very low load current (100ma) and measuring the ringing frequency. csnub and rsnub can be calculated from equations 26 and 27: input capacitor selection the input capacitor absorbs the ripple current from the synchronous buck converter, which is given by equation 28: this rms ripple current must be smaller than the rated rms current in the capacitor datas heet. non-tantalum chemistries (ceramic, aluminum, or oscon) are preferred due to their resistance to power-up surge currents when the ac adapter is plugged into the battery charger. for notebook battery charger applications, it is recommended that ceramic capacitors or polymer capacitors from sanyo be used due to their small size and reasonable cost. table 2 shows the component lists for the typical application circuit in figure 2. loop compensation design isl6252 has three closed loop control modes. one controls the output voltage when the battery is fully charged or absent. a second controls the current into the battery when charging and the third limits cu rrent drawn from the adapter. the charge current and input current control loops are compensated by a single capacitor on the icomp pin. the voltage control loop is comp ensated by a network on the vcomp pin. descriptions of these control loops and guidelines for selecting compensation components will be given in the following sections. which loop controls the output is determined by the minimum current buffer and the minimum voltage buffer shown in figure 1. these three loops will be described separately. transconductance amplifiers gm1, gm2 and gm3 the isl6252 uses several transconductance amplifiers (also known as gm amps). most commercially available op amps are voltage controlled voltage sources with gain expressed as a = v out /v in . transconductance amps are voltage controlled current sources with gain expressed as gm = i out /v in . transconductance gain (gm) will appear in some of the equations for poles and zeros in the compensation. pwm gain f m the pulse width modulator in the isl6252 converts voltage at vcomp to a duty cycle by comparing vcomp to a triangle wave (duty = vcomp/v p-p ramp ). the low-pass filter formed by l and c o convert the duty cycle to a dc output voltage (vo = v dcin *duty). in isl6252, the triangle wave amplitude is proportional to v dcin . making the ramp amplitude proportional to dcin makes the gain from vcomp to the phase output a constant 11 and is independent of dcin. for small signal ac analysis, the battery is modeled by it?s internal resistance. the total output resistance is the sum of the sense resistor and the internal resistance of the mosfets, inductor and capacitor. figure 18 shows the small signal model of the pulse width modulator (pwm), power stage , output filter and battery. table 2. component list parts part numbers and manufacturer c 1 , c 10 10f/25v ceramic capacitor, taiyo yuden tmk325 mj106my x5r (3.2mmx2.5mmx1.9mm) c 2 , c 4 , c 8 0.1f/50v ceramic capacitor c 3 , c 7 , c 9 1f/10v ceramic capacitor, taiyo yuden lmk212bj105mg c 5 10nf ceramic capacitor c 6 6.8nf ceramic capacitor c 11 3300pf ceramic capacitor d 1 30v/3a schottky diode, ec31qs03l (optional) d 2 100ma/30v schottky diode, central semiconductor l 10h/3.8a/26m , sumida, cdrh104r-100 q 1 , q 2 30v/35m , fds6912a, fairchild q 6 signal n-channel mosfet, 2n7002 r 1 40m , 1%, lrc-lr2512-01-r040-f, irc r 2 20m , 1%, lrc-lr2010-01-r020-f, irc r 3 18 , 5%, (0805) r 4 2.2 , 5%, (0805) r 5 100k , 5%, (0805) r 6 4.7k, 5%, (0805) c snub 2 2 f ring () 2 l ? ------------------------------------ - = (eq. 26) r snub 2l ? c snub ------------------- - = (eq. 27) i rms i bat v out v in v out ? () ? v in ------------------------------------------------------------- = (eq. 28) r 7 100 , 5%, (0805) r 8 , r 11 130k, 1%, (0805) r 9 10.2k , 1%, (0805) r 10 4.7 , 5%, (0805) r 12 20k , 1%, (0805) r 13 1.87k , 1%, (0805) table 2. component list (continued) parts part numbers and manufacturer isl6252, isl6252a
19 fn6498.3 august 25, 2010 in most cases the battery resistance is very small (<200m ) resulting in a very low q in the output filter. this results in a frequency response from the input of the pwm to the inductor current with a single pole at the frequency calculated in equation 29: the output capacitor creates a pole at a very high frequency due to the small resistance in parallel with it. the frequency of this pole is calculated in equation 30: charge current control loop when the battery voltage is less than the fully charged voltage, the voltage error amplifier goes to it?s maximum output (limited to 1.2v a bove icomp) and the icomp voltage controls the loop through the minimum voltage buffer. figure 19 shows the charge current control loop. the compensation capacitor (c icomp ) gives the error amplifier (gmi) a pole at a very low frequency (<<1hz) and a a zero at f z1 . f z1 is created by the 0.25*ca2 output added to icomp. the frequency of can be calculated from equation 31: placing this zero at a frequency equal to the pole calculated in equation 29 will result in maximum gain at low frequencies and phase margin near 90. if the zero is at a higher frequency (smaller c icomp ), the dc gain will be higher but the phase margin will be lower. use a capacitor on icomp that is equal to or greater than the value calculated in equation 32: a filter should be added between r s2 and csop and cson to reduce switching noise. the filter roll off frequency should be between the crossover frequency and the switching frequency (~100khz). r f2 should be small (<10 ) to minimize offsets due to leakage current into csop. the filter cut-off frequency is calculated using equation 33: the crossover frequency is determined by the dc gain of the modulator and output filter and the pole in equation 29. the dc gain is calculated in equation 34 and the crossover frequency is calculated with equation 35. figure 18. small signal ac model drivers ramp gen v ramp = vdd/11 vdd - + 11 pwm input l co l r esr co r sense r bat r fet_r ds(on) pwm input r l_dcr pwm gain = 11 f pole1 r sense r ds on () r dcr r bat +++ () 2 l ? ------------------------------------------------------------------------------------------------------ - = (eq. 29) f pole2 1 2 c o r bat ?? -------------------------------------- - = (eq. 30) figure 19. charge current limit loop r s2 r bat icomp cson phase r esr c o 11 + - ca2 20 csop s + - 0.25 chlim - + + - gm2 c f2 r f2 c icomp l r fet _r ds(on) r l_dcr f zero 4gm2 ? 2 c icomp ? () --------------------------------------- = (eq. 31) gm2 50 a v -------------- - = c icomp 450 av ? () ? r s2 r ds on () r dcr r bat +++ () ------------------------------------------------------------------------------------------ = (eq. 32) f filter 1 2 c f2 r f2 ?? () ------------------------------------------ - = (eq. 33) a dc 11 r ? s2 r s2 r ds on () r dcr r battery +++ () --------------------------------------------------------------------------------------------------------- - = (eq. 34) f co a dc f pole1 ? 11 r ? s2 2 l ? ---------------------- == (eq. 35) isl6252, isl6252a
20 fn6498.3 august 25, 2010 the bode plot of the loop gain, the compensator gain and the power stage gain is shown in figure 20: adapter current limit control loop if the combined battery charge current and system load current draws current that eq uals the adapter current limit set by the aclim pin, isl6252 will reduce the current to the battery and/or reduce the output voltage to hold the adapter current at the limit. above the adapter current limit, the minimum current buffer equals the output of gm3 and icomp controls the charger output. figure 21 shows the adapter current limit control loop. . the loop response equations, bode plots and the selection of c icomp are the same as the charge current control loop with loop gain reduced by the duty cycle and the ratio of r s1 /r s2 . in other words, if r s1 = r s2 and the duty cycle d = 50%, the loop gain will be 6db lower than the loop gain in figure 20. this gives lower crossover frequency and higher phase margin in this mode. if r s1 /r s2 = 2 and the duty cycle is 50% then the adapter current loop gain will be identical to the gain in figure 20. a filter should be added between r s1 and csip and csin to reduce switching noise. the filt er roll off frequency should be between the crossover frequency and the switching frequency (~100khz). voltage control loop when the battery is charged to the voltage set by cells and vadj the voltage error amplifier (gm1) takes control of the output (assuming that the adapter current is below the limit set by aclim). the voltage error amplifier (gm1) discharges the capacitor on vcomp to limit the output voltage. the current to the battery decreases as the cells charge to the fixed voltage and the voltage across the internal battery resistance decreases. as battery current decreases the 2 current error amplifiers (gm2 and gm3) output their maximum current and charge the capacitor on icomp to its maximum voltage (limited to 1.2v above vcomp). with high voltage on icomp, the minimum voltage buffer output equals the voltage on vcomp. the voltage control loop is shown in figure 22. . output lc filter transfer functions the gain from the phase node to the system output and battery depend entirely on external components. typical output lc filter response is shown in figure 23. transfer function a lc (s) is shown in equation 36: -60 -40 -20 0 20 40 60 0.01k 0.1k 1k 10k 100k 1m frequency (hz) gain (db) compensator modulator loop f zero f pole1 f filter f pole2 figure 20. charge current loop bode plots c icomp icomp phase 11 + - 0.25 aclim - + + - gm3 r s1 dcin csin + - ca1 20 csip c f1 r f1 r cson + - ca2 20 csop c f2 r f2 r esr c o l r fet _r ds(on) r l_dcr figure 21. adapter current limit loop figure 22. voltage control loop vcomp cson phase 11 csop + - 0.25 - + + - gm1 c vcomp r vcomp 2.1v r3 r4 + - ca2 20 r s2 r bat r esr c o c f2 r f2 l r fet _r ds(on) r l_dcr a lc 1 s esr --------------- ? ?? ?? s 2 dp ----------- - s lc q ? () ------------------------ - 1 ++ ?? ?? ?? ----------------------------------------------------------- = (eq. 36) esr 1 r esr c o ? () -------------------------------- - = lc 1 lc o ? () ----------------------- - = qr o l c o ------ - ? = isl6252, isl6252a
21 fn6498.3 august 25, 2010 the resistance r o is a combination of mosfet r ds(on) , inductor dcr, r sense and the internal resistance of the battery (normally between 50m and 200m ). the worst case for voltage mode control is when the battery is absent. this results in the highest q of the lc filter and the lowest phase margin. the compensation network cons ists of the voltage error amplifier gm1 and the compensation network r vcomp , c vcomp , which give the loop very high dc gain, a very low frequency pole and a zero at f zero1 . inductor current information is added to the feedback to create a second zero, f zero2 . the low pass filter r f2 , c f2 between r sense and isl6252 add a pole at f filter . r 3 and r 4 are internal divider resistors that set the dc output voltage. for a 3-cell battery, r 3 = 320k and r 4 = 64k . equations 37, 38, 39, 40, 41 and 42 relate the co mpensation network?s poles, zeros and gain to the components in figure 22. figure 24 shows an asymptotic bode pl ot of the dc/dc converter?s gain vs frequency. it is strongly recommended that f zero1 is approximately 30% of f lc and f zero2 is approximately 70% of f lc . compensation break frequency equations figure 23. frequency response of the lc output filter phase () gain (db) frequency -60 -50 -40 -30 -20 -10 0 10 20 100 200 500 1k 2k 5k 10k 20k 50k 100k 200k 500k -160 -140 -120 -100 -80 -60 -40 -20 no battery r battery = 50m r battery = 200m -60 -40 -20 0 20 40 0.1k 1k 10k 100k 1m frequency (hz) gain (db) compensator modulator loop f lc f pole1 f zero1 f zero2 f esr f filter figure 24. asymptotic bode plot of the voltage control loop gain f zero1 1 2 c vcomp r 1comp ?? () ---------------------------------------------------------------------- - = (eq. 37) f zero2 r vcomp 2 r sense c ? out ? -------------------------------------------------------- ?? ?? ?? r 4 r 4 r 3 + -------------------- - ?? ?? ?? gm1 5 ------------ ?? ?? ?? = (eq. 38) f lc 1 2 lc o ? () ------------------------------- = (eq. 39) f filter 1 2 r f2 c f2 ?? () ------------------------------------------ - = (eq. 40) f pole1 1 2 r sense c o ?? () --------------------------------------------------- - = (eq. 41) f esr 1 2 c o r esr ?? () -------------------------------------------- = (eq. 42) isl6252, isl6252a
22 fn6498.3 august 25, 2010 choose r vcomp equal or lower than the value calculated from equation 43: next, choose c vcomp equal or higher than the value calculated from equation 44: pcb layout considerations power and signal layers placement on the pcb as a general rule, power layers should be close together, either on the top or bottom of the board, with signal layers on the opposite side of the boar d. as an example, layer arrangement on a 4-layer board is shown in the following: 1. top layer: signal lines, or half board for signal lines and the other half board for power lines 2. signal ground 3. power layers: power ground 4. bottom layer: power mosfet, inductors and other power traces separate the power voltage and current flowing path from the control and logic level signal path. the controller ic will stay on the signal layer, which is isolated by the signal ground to the power signal traces. component placement the power mosfet should be close to the ic so that the gate drive signal, the lgate, ugate, phase, and boot, traces can be short. place the components in such a way that the area under the ic has less noise traces with high dv/dt and di/dt, such as gate signals and phase node signals. signal ground and power ground connection at minimum, a reasonably large area of copper, which will shield other noise couplings through the ic, should be used as signal ground beneath the ic. the best tie-point between the signal ground and the power ground is at the negative side of the output capacitor on each side, where there is little noise; a noisy trace beneath the ic is not recommended. gnd and vdd pin at least one high quality ceramic decoupling capacitor should be used to cross these two pins. the decoupling capacitor can be put close to the ic. lgate pin this is the gate drive signal for the bottom mosfet of the buck converter. the signal going through this trace has both high dv/dt and high di/dt, and the peak charging and discharging current is very hi gh. these two traces should be short, wide, and away from other traces. there should be no other traces in parallel wit h these traces on any layer. pgnd pin pgnd pin should be laid out to the negative side of the relevant output capacitor with separate traces.the negative side of the output capacitor must be close to the source node of the bottom mosfet. this trace is the return path of lgate. phase pin this trace should be short, and positioned away from other weak signal traces. this node has a very high dv/dt with a voltage swing from the input voltage to ground. no trace should be in parallel with it. this trace is also the return path for ugate. connect this pi n to the high-side mosfet source. ugate pin this pin has a square shape waveform with high dv/dt. it provides the gate drive current to charge and discharge the top mosfet with high di/dt. this trace should be wide, short, and away from other traces similar to the lgate. boot pin this pin?s di/dt is as high as the ugate; therefore, this trace should be as short as possible. csop, cson, csip and csin pins accurate charge current and adapter current sensing is critical for good performance. the current sense resistor connects to the cson and the csop pins through a low pass filter with the filter capacitor very near the ic (see figure 2). traces from the sens e resistor should start at the pads of the sense resistor and should be routed close together, throughout the low pass filter and to the cson and cson pins (see figure 25). the cson pin is also used as the battery voltage feedback. the traces should be routed away from the high dv/dt and di/dt pins like phase, boot pins. in general, the current sense resistor should be close to the ic. these guidelines should also be followed for the adapter current sense resistor and csip and csin. other layout arrangements should be adjusted accordingly. table 3. cells r 3 r 4 2 288k 48k 3 320k 64k 4 336k 96k vcomp 0.7 f lc ? () 2 c o r sense ?? () 5 gm1 ------------ ?? ?? r 3 r 4 + r 4 -------------------- - ?? ?? ?? ??? = (eq. 43) c vcomp 1 0.3 f lc ? () 2 r vcomp ? () ? ------------------------------------------------------------------------ - = (eq. 44) isl6252, isl6252a
23 fn6498.3 august 25, 2010 . en pin this pin stays high at enable mode and low at idle mode and is relatively robust. enable signals should refer to the signal ground. dcin pin this pin connects to ac adapter output voltage, and should be less noise sensitive. copper size for the phase node the capacitance of phase shoul d be kept very low to minimize ringing. it would be best to limit the size of the phase node copper in strict accordance with the current and thermal management of the application. identify the power and signal ground the input and output capacitors of the converters, the source terminal of the bottom swit ching mosfet pgnd should connect to the power ground. the other components should connect to signal ground. signal and power ground are tied together at one point. clamping capacitor for switching mosfet it is recommended that ceramic capacitors be used closely connected to the drain of t he high-side mosfet, and the source of the low-side mosfet . this capacitor reduces the noise and the power loss of the mosfet. high current trace high current trace kelvin connection traces to the low pass filter and csop and cson sense resistor figure 25. current sense resistor layout resistor isl6252, isl6252a
24 fn6498.3 august 25, 2010 isl6252, isl6252a package outline drawing l28.5x5 28 lead quad flat no-lead plastic package rev 2, 10/07 located within the zone indicated. the pin #1 identifier may be unless otherwise specified, tolerance : decimal 0.05 tiebar shown (if present) is a non-functional feature. the configuration of the pin #1 identifier is optional, but must be between 0.15mm and 0.30mm from the terminal tip. dimension b applies to the metallized terminal and is measured dimensions in ( ) for reference only. dimensioning and tolerancing conform to amse y14.5m-1994. 6. either a mold or mark feature. 3. 5. 4. 2. dimensions are in millimeters. 1. notes: bottom view detail "x" typical recommended land pattern top view bottom view side view 5.00 a 5.00 b index area pin 1 6 (4x) 0.15 28x 0.55 0.10 4 a 28x 0.25 m 0.10 c b 14 8 4x 0.50 24x 3.0 6 pin #1 index area 3 .10 0 . 15 0 . 90 0.1 base plane see detail "x" seating plane 0.10 c c 0.08 c 0 . 2 ref c 0 . 05 max. 0 . 00 min. 5 ( 3. 10) ( 4. 65 typ ) ( 24x 0 . 50) (28x 0 . 25 ) ( 28x 0 . 75) 15 22 21 7 1 28 + 0.05 - 0.07
25 all intersil u.s. products are manufactured, asse mbled and tested utilizing iso9000 quality systems. intersil corporation?s quality certifications ca n be viewed at www.intersil.com/design/quality intersil products are sold by description only. intersil corpor ation reserves the right to make changes in circuit design, soft ware and/or specifications at any time without notice. accordingly, the reader is cautioned to verify that data sheets are current before placing orders. information furnishe d by intersil is believed to be accurate and reliable. however, no responsibility is assumed by intersil or its subsidiaries for its use; nor for any infringements of paten ts or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of intersil or its subsidiari es. for information regarding intersil corporation and its products, see www.intersil.com fn6498.3 august 25, 2010 isl6252, isl6252a shrink small outline plastic packages (ssop) quarter size outline plastic packages (qsop) notes: 1. symbols are defined in the ?mo se ries symbol list? in section 2.2 of publication number 95. 2. dimensioning and tolerancing per ansi y14.5m - 1982. 3. dimension ?d? does not include mo ld flash, protrusions or gate burrs. mold flash, protrusion and gate burrs shall not exceed 0.15mm (0.006 inch) per side. 4. dimension ?e? does not include interlead flash or protrusions. interlead flash and protrusions shall not exceed 0.25mm (0.010 inch) per side. 5. the chamfer on the body is optional . if it is not present, a visual index feature must be located within the crosshatched area. 6. ?l? is the length of terminal for soldering to a substrate. 7. ?n? is the number of terminal positions. 8. parameters with min and/or max limits are 100% tested at +25c, unless otherwise specified. temperature limits established by ch aracterization and are not production tested. 9. dimension ?b? does not include dambar protrusion. allowable dambar protrusion shall be 0.10mm (0.004 inch) total in excess of ?b? dimension at maxi mum material condition. index area e d n 123 -b- 0.17(0.007) c a m bs e -a- b m -c- a1 a seating plane 0.10(0.004) h x 45 c h 0.25(0.010) b m m l 0.25 0.010 gauge plane a2 m24.15 24 lead shrink small outline plastic package (0.150? wide body) symbol inches millimeters notes min max min max a 0.053 0.069 1.35 1.75 - a1 0.004 0.010 0.10 0.25 - a2 - 0.061 - 1.54 - b 0.008 0.012 0.20 0.30 9 c 0.007 0.010 0.18 0.25 - d 0.337 0.344 8.55 8.74 3 e 0.150 0.157 3.81 3.98 4 e 0.025 bsc 0.635 bsc - h 0.228 0.244 5.80 6.19 - h 0.0099 0.0196 0.26 0.49 5 l 0.016 0.050 0.41 1.27 6 n24 247 0 8 0 8 - rev. 2 6/04

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