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general description ________________ the MAX1640/max1641 cmos, adjustable-output, switch-mode current sources operate from a +5.5v to +26v input, and are ideal for microprocessor-controlled battery chargers. charging current, maximum output voltage, and pulse-trickle charge are programmed with external resistors. programming the off-time modifies the switching frequency, suppressing undesirable har- monics in noise-sensitive circuits. the MAX1640? high- side current sensing allows the load to connect directly to ground, eliminating ground-potential errors. the max1641 incorporates a low-side current sense. the MAX1640/max1641 step-down pulse-width-modu- lation (pwm) controllers use an external p-channel mosfet switch and an optional, external n-channel mosfet synchronous rectifier for increased efficiency. an internal low-dropout linear regulator provides power for the internal reference and circuitry as well as the gate drive for the n-channel synchronous rectifier. the MAX1640/max1641 are available in space-saving, 16-pin narrow qsop packages. ________________________applications battery-powered equipment laptop, notebook, and palmtop computers handy terminals portable consumer products cordless phones cellular phones pcs phones backup battery charger ____________________________features ? 95% efficiency ? +5.5v to +26v input supply range ? 2v to 24v adjustable-output voltage range ? 100% maximum duty cycle (low dropout) ? up to 500khz pwm operation ? optional synchronous rectifier ? 16-pin qsop package ? current-sense accuracy: 2% (max1641), 5.3% (MAX1640) MAX1640/max1641 adjustable-output, switch-mode current sources with synchronous rectifier ________________________________________________________________ maxim integrated products 1 pin configuration 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 ldol in ldoh pdrv ndrv pgnd cs+ cs- gnd top view MAX1640 max1641 qsop toff d1 ref d0 cc set term 19-1245; rev 1; 1/02 part MAX1640 c/d MAX1640eee max1641 c/d 0 c to +70 c -40 c to +85 c 0 c to +70 c temp. range pin-package dice* 16 qsop dice* __________________ ______________________ ordering information * dice are specified at t a = +25 c, dc parameters only. max1641eee -40 c to +85 c 16 qsop in ldoh pdrv ndrv p pgnd cs+ cs- term ldol gnd out d0 v in = +5.5v to +26v d1 toff r toff ref set cc MAX1640 _____________ typical operating circuit evaluation kit available for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = +12v, v out = 6v, circuit of figure 2, t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. note 1: this ratio is generated by a 1:8 clock divider and is not an error source for current calculations. in to gnd ............................................................... -0.3v to +28v ldoh to in ............................................................... +0.3v to -6v ldol to gnd ........................................................... -0.3v to +6v pdrv to gnd .............................. (v ldoh - 0.3v) to (v in + 0.3v) ndrv to gnd ......................................... -0.3v to (v ldol + 0.3v) toff, ref, set, term, cc to gnd ...... -0.3v to (v ldol + 0.3v) d0, d1 to gnd ......................................................... -0.3v to +6v cs+, cs- to gnd ................................................... -0.3v to +28v pgnd to gnd ..................................................................... 0.3v continuous power dissipation (t a = +70 c) qsop (derate 8.30mw/ c above +70 c) ................... 667mw operating temperature range max164_eee ................................................... -40 c to +85 c storage temperature range ............................. -65 c to +150 c lead temperature (soldering, 10sec) ............................ +300 c i ref = 0 to 50 a d0 = d1 = low d0 = d1 = low (off mode) d0 or d1 = high v out = 2v to 24v v in = v out + 0.5v to 26v max1641 max1641 MAX1640 v in = 5.5v to 26v, i load = 0 to 20ma v in = 5.5v to 26v, i load = 0 to 20ma MAX1640 conditions a 1 v set input current mv 4 10 reference load regulation v 1.96 2.00 2.04 v ref reference voltage v 4.05 4.20 4.35 v ldol undervoltage lockout a 1 output current in off mode 500 ma 2 4 quiescent v in supply current 0.1 %/v 0.1 0.4 output current compliance %/v 0.03 current-sense line regulation 34 37.5 41 mv 36 42 48 147 150 153 mv 142 150 158 full-scale current-sense threshold v v in - v in - v in - 5.5 5.0 4.5 v ldoh linear-regulator output voltage, v in referenced v 4.5 5.0 5.5 v ldol linear-regulator output voltage, ground referenced units min typ max symbol parameter v 5.5 26 v in input voltage range fet drive output resistance pfet and nfet drive 12 off-time range 1 10 s off-time accuracy r toff = 62k 1.7 2.2 2.7 s pulse-trickle mode duty-cycle period d0 = low, d1 = high, r toff = 100k 27 33 40 ms pulse-trickle mode duty cycle (note 1) d0 = low, d1 = high, r toff = 100k 12.5 % quarter-scale current-sense threshold MAX1640 max1641 a
MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier _______________________________________________________________________________________ 3 electrical characteristics (v in = +12v, v out = 6v, circuit of figure 2, t a = -40?c to +85?c , unless otherwise noted.) i ref = 0 to 50 a v out = 2v to 24v (MAX1640) d0 = d1 = low d0 or d1 = high fet drive output resistance max1641 MAX1640 v in = 5.5v to 26v, i load = 0 to 20ma v in = 5.5v to 26v, i load = 0 to 20ma MAX1640 conditions a 1 v set input current mv 10 reference load regulation v 1.94 2.06 v ref reference voltage v 4.0 4.4 v ldol undervoltage lockout a 1 output current in off mode ma 4 quiescent v in supply current %/v 0.4 output current compliance mv 34 48 quarter-scale current-sense threshold 12 ? off-time range v 5.5 26 v in input voltage range 1.5 8 s off-time accuracy r toff = 62k ? 1.5 2.5 s 146 154 pulse-trickle mode duty-cycle period mv 141 159 full-scale current-sense threshold v v in - v in - 5.5 4.5 v ldoh linear-regulator output voltage, v in referenced d0 = low, d1 = high, r toff = 50k ? 25 42 ms v 4.5 5.5 v ldol linear-regulator output voltage, ground referenced units min typ max symbol parameter pwm maximum duty cycle 100 % input low voltage v il d0, d1 0.8 v input high voltage v ih d0, d1 2.4 v input leakage current i in d0, d1 1 a 33 42 max1641 electrical characteristics (continued) (v in = +12v, v out = 6v, circuit of figure 2, t a = 0?c to +85?c , unless otherwise noted. typical values are at t a = +25?c.) conditions units min typ max symbol parameter pwm maximum duty cycle 100 % input low voltage v il d0, d1 0.8 v input high voltage v ih d0, d1 2.4 v input leakage current i in d0, d1 1 a
MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier 4 _______________________________________________________________________________________ 0.45 0.51 0.49 0.47 0.53 0.55 0.57 0.59 0.61 0.63 0.65 4 12 8 16 20 24 28 off-mode supply current (no-load) MAX1640/41-toc07 input voltage (v) off-mode supply current (ma) t a = -40? t a = +25? t a = +85? 10,000 1 0 50 100 150 200 250 300 350 400 switching frequency vs. r toff MAX1640/41 toc 08 t off (k w ) switching frequency (khz) 10 100 1000 v out = +3v v out = +6v __________________________________________ t ypical operating characteristics (circuit of figure 2, t a = +25 c, unless otherwise noted.) 40 60 50 80 70 90 100 2 6 8 10 4 12 14 16 18 20 22 24 efficiency vs. output voltage MAX1640/41-toc01 output voltage (v) efficiency (%) v in = 12v v in = 18v v in = 26v 1.460 1.470 1.480 1.490 1.500 1.510 4 12 8 16 20 24 28 MAX1640 output current vs. input voltage MAX1640/41 toc02 input voltage (v) output current (a) t a = -40? (v out = 4v) t a = +25? t a = +85? 1.450 1.470 1.460 1.490 1.480 1.500 1.510 2 6 8 10 4 12 14 16 18 20 22 24 MAX1640 output current vs. output voltage MAX1640/41-toc03 output voltage (v) output current (a) t a = -40? t a = +85? t a = +25? 1.450 1.475 1.500 1.525 1.550 4 12 8 16 20 24 28 max1641 output current vs. input voltage MAX1640/41 toc04 input voltage (v) output current (a) t a = -40? (v out = 4v) t a = +25? t a = +85? 1.420 1.460 1.440 1.500 1.480 1.540 1.520 1.560 2 6 8 10 4 12 14 16 18 20 22 24 max1641 output current vs. output voltage MAX1640/41-toc05 v out (v) output current (a) t a = -40? t a = +25? t a = +85? 1.5 1.9 1.7 2.1 2.3 2.5 2.7 2.9 4 12 8 16 20 24 28 quiescent current vs. input voltage (no-load) MAX1640/41-toc06 input voltage (v) quiescent current (ma) t a = -40? t a = +25? t a = +85? a: output current, d1 = d0 = 1 1a/div v load = 3v b: input voltage, 10v/div line-transient response a b 0a 0v 2ms/div MAX1640/41 toc 09
MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier _______________________________________________________________________________________ 5 ____________________________ t ypical operating characteristics (continued) (circuit of figure 2, t a = +25 ? c, unless otherwise noted.) a: output current, d0 = d1 = 0 1a/div v in = 12v, v set = 1v, r load = 4 w, no output capacitor b: load voltage, ac coupled, 500mv/div current-mode change response time a b 2ms/div 0a 0v MAX1640/41 toc 10 b a exiting off mode MAX1640/41 toc11 a: d0 = d1 = 1 2v/div v in = 12v, r load = 4 w b: output current, 0.5a/div 20 m s/div ______________________________________________________________ pin description name function 1 ldol internal, ground-referenced low-dropout linear regulator output. bypass with a 0.1 f capacitor in parallel with a 4.7 f capacitor to gnd. 2 toff off-time select input. a resistor (r toff ) connected from this pin to gnd programs the off-time for the hys - teretic pwm step-down converter. this resistor also sets the period in duty-cycle mode. see duty-cycle mode and programming the off-time. pin 3, 4 d1, d0 digital inputs. select mode of operation (table 1). 5 cc constant-current loop compensation input. bypass with a 0.01 f capacitor to gnd. 8 term maximum output voltage termination input. when v term exceeds the reference voltage, the comparator resets the internal pwm latch, shutting off the external p-channel fet. 7 set current select input. program the desired current level by applying a voltage at set between 0v and v ref , (i = v set / 13.3r sense ). see figure 3. 6 ref reference voltage output (v ref = 2v). bypass with a 0.1 f capacitor to gnd. 13 ndrv gate drive for an optional n-channel fet synchronous rectifier 12 pgnd high-current ground return for the output drivers 11 cs+ positive current-sense comparator input 10 cs- negative current-sense comparator input 9 gnd ground 14 pdrv gate drive for the p-channel fet 15 ldoh internal, input-referenced low-dropout linear regulator output. bypass with a 0.33 f capacitor to in. 16 in power-supply input. input of the internal, low-dropout linear regulators.
MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier 6 _______________________________________________________________________________________ mode control cc toff d0, d1 term ref set cs- cs+ reg pdrv ndrv pgnd in ldol ldoh a1 a2 gm mux b a sel MAX1640 max1641 figure 1. MAX1640/max1641 functional diagram
MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier _______________________________________________________________________________________ 7 _______________ detailed description the MAX1640/max1641 switch-mode current sources utilize a hysteretic, current-mode, step-down pulse- width-modulation (pwm) topology with constant off- time. internal comparators control the switching mechanism. these comparators monitor the current through a sense resistor (r sense ) and the voltage at term. when inductor current reaches the current limit [(v cs+ - v cs- ) / r sense ], the p-channel fet turns off and the n-channel fet synchronous rectifier turns on. inductor energy is delivered to the load as the current ramps down. this ramp rate depends on r toff and inductor values. when off-time expires, the p-channel fet turns back on and the n-channel fet turns off. two digital inputs, d0 and d1, select between four pos - sible current levels (table 1). in pulse-trickle mode, the part operates for 12.5% of the period set by r toff , resulting in a lower current for pulse-trickle charging. figure 1 is the MAX1640/max1641 functional diagram. figure 2 shows the standard application circuits. charge mode: programming the output currents the sense resistor, r sense , sets two charging current levels. choose between these two levels by holding d0 high, and toggling d1 either high or low (table 1). the fast-charge current level equals v cs / r sense where v cs is the full-scale current-sense voltage of 150mv. alternatively, calculate this current by v ref / (13.3r sense ). the top-off current equals v set / (13.3r sense ). a resistor-divider from ref to gnd pro - grams the voltage at set (figure 3). p n 0.1 m f 4.7 m f 47 m f 0.33 m f 0.01 m f 0.1 m f r1 r toff r2 set ref toff d1 d0 ldol pdrv ndrv pgnd cs+ cs- term gnd cc r3 47 m h v out batt 1/2 ir7309 1/2 ir7309 r4 100m w ldoh in max1641 p n 0.1 m f 0.01 m f 4.7 m f 47 m f 0.33 m f 0.1 m f r1 r2 set ref toff d1 d0 ldol pdrv ndrv pgnd cs+ cs- r3 r4 term gnd cc 47 m h 1/2 ir7309 1/2 ir7309 100m w batt v out r toff ldoh in MAX1640 figure 2a. standard application circuit figure 2b. standard application circuit
MAX1640/max1641 the voltage at set is given by: r1 = r2 (v ref / v set -1 ); 10k ? < r2 < 300k ? where v ref = 2v and v set is proportional to the desired output current level. the MAX1640/max1641 are specified for v set between 0v and v ref . for v set > v ref , output current increases linearly (with reduced accuracy) until it clamps at v set ? 4v. pulse-trickle mode: selecting the pulse-trickle current pulling d0 low and d1 high selects pulse-trickle mode. this current equals v set / (13.3r sense ) and remains on for 12.5% of the period set by r toff . pulse-trickle current maintains full charge across the battery and can slowly charge a cold battery before fast charging commences. off mode: turning off the output current pulling d0 and d1 low turns off the p-channel fet and hence the output current flow. this mode also controls end of charge and protects the battery against exces - sive temperatures. setting the maximum output voltage level the maximum output voltage should be programmed to a level higher than the output/battery voltage (i load x r load ). an external resistor-divider between the output and ground (figure 4) sets the voltage at term. once the voltage at term exceeds the reference, the internal comparator turns off the p-channel fet, terminating current flow. select r4 in the 10k ? to 500k ? range. r3 is given by: r3 = r4 (v out / v term ) -1 period = 3.2 x 10 x r (sec) -7 toff adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier 8 _______________________________________________________________________________________ d1 do mode output current (a) 0 0 off 0 0 1 top-off v set / (13.3r sense ) 1 0 pulse-trickle v set / (13.3r sense ) 12.5% duty cycle 1 1 fast charge v ref / (13.3r sense ) table 1. selecting output current levels MAX1640 max1641 ref set r1 r2 figure 3. adjusting the output current level MAX1640 cs+ term cs- r3 r sense batt l r4 figure 4a. setting the maximum output voltage level max1641 cs+ term cs- r3 batt r4 r sense l figure 4b. setting the maximum output voltage level
where v term = 2v and v out is the desired output voltage. programming the off-time when programming the off-time, consider such factors as maximum inductor current ripple, maximum output voltage, inductor value, and inductor current rating. the output current ripple is less than the inductor current rip - ple and depends heavily on the output capacitor?s size. perform the following steps to program the off-time: 1) select the maximum output current ripple. i r (a) 2) select the maximum output voltage. v out (max)(v) 3) calculate the inductor value range as follows: l min = (v outmax x 1 s) / i r l max = (v outmax x 10 s) / i r 4) select an inductor value in this range. 5) calculate t off as follows: 6) program t off by selecting r toff from: r toff = (29.3 x 10 9 ) x t off 7) calculate the switching frequency by: fs = 1 / (t on + t off ) where t on = (i r x l) / (v in - v out ) and i r = (v out x t off ) / l. l is the inductor value, v in is the input volt - age, v out is the output voltage, and i r is the output peak-to-peak current ripple. note that r toff sets both the off-time and the pulse- trickle charge period. reference the on-chip reference is laser trimmed for a precise 2v at ref. ref can source no more than 50 a. bypass ref with a 0.1 f capacitor to ground. constant-current loop: ac loop compensation the constant-current loop?s output is brought out at cc. to reduce noise due to variations in switching currents, bypass cc with a 1nf to 100nf capacitor to ground. a large capacitor value maintains a constant average out - put current but slows the loop response to changes in switching current. a small capacitor value speeds up the loop response to changes in switching current, generating increased ripple at the output. select c cc to optimize the ripple vs. loop response. synchronous rectification synchronous rectification reduces conduction losses in the rectifier by shunting the schottky diode with a low- resistance mosfet switch. in turn, efficiency increases by about 3% to 5% at heavy loads. to prevent cross- conduction or shoot-through, the synchronous rectifier turns on shortly after the p-channel power mosfet turns off. the synchronous rectifier remains off for 90% of the off-time. in low-cost designs, the synchronous rectifier fet may be replaced by a schottky diode. component selection external switching transistors the MAX1640/max1641 drive an enhancement-mode p-channel mosfet and a synchronous-rectifier n- channel mosfet (table 2). when selecting a p-channel fet, some important para - meters to consider are on-resistance (r ds(on) ), maxi - mum drain-to-source voltage (v ds max), maximum gate-to-source voltage (v gs max), and minimum threshold voltage (v th min). in high-current applications, mosfet package power dissipation often becomes a dominant design factor. i 2 r power losses are the greatest heat contributor for both high-side and low-side mosfets. switching loss - es affect the upper mosfet only (p-channel), since the schottky rectifier or the n-fet body diode clamps the switching node before the synchronous rectifier turns on. rectifier diode if an n-channel mosfet synchronous rectifier is not used, a schottky rectifier is needed. the MAX1640/ t = l x i v off r outmax MAX1640/max1641 adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier _______________________________________________________________________________________ 9 table 2. component manufacturers component manufacturer mosfets sense resistor capacitors international rectifier dale avx sumida coilcraft inductor coiltronics siliconix s14539dy irf7309 wsl-2010 series tps series mbar5340t3 cdrh125 series d03316p series up2 series irc lr2010-01 series sprague 595d series nihon nsq03a04 rectifier in5817-in5822 motorola
MAX1640/max1641 max1641?s high switching frequency demands a high- speed rectifier (table 2). schottky diodes such as the 1n5817e1n5822 are recommend ed. make sure the schottky diode?s average current rating exceeds the peak current limit and that its breakdown voltage exceeds the output voltage (v out ). for high-tempera - ture applications, schottky diodes may be inadequate due to their high leakage current; high-speed silicon diodes such as the mur105 or ec11fs1 can be used instead. at heavy loads and high temperatures, the benefits of a schottky diode?s low forward voltage may outweigh the disadvantage of high leakage current. if the application uses an n-channel mosfet synchro - nous rectifier, a parallel schottky diode is usually unnecessary except with very high charge current (> 3 amps). best efficiency is achieved with both an n-channel mosfet and a schottky diode. inductor value refer to the section programming the off-time to select the proper inductor value. there is a trade-off between inductor value, off-time, output current ripple, and switching frequency. __________ applications infor mation all-purpose microcontroller battery charger: nicd, nimh in applications where a microcontroller is available, the MAX1640/max1641 can be used as a low-cost battery charger (figure 5). the controller takes over fast charge, pulse-trickle charge, charge termination, and other smart functions. by monitoring the output voltage at v out , the controller initiates fast charge (set d0 and d1 high), terminates fast charge and initiates top-off (set d0 high and d1 low), enters trickle charge (set d0 low and d1 high), or shuts off and terminates current flow (set d0 and d1 low). layout and grounding due to high current levels and fast switching wave - forms, proper pc board layout is essential. high-cur - rent ground paths should be connected in a star adjustable-output, switch-mode cur r ent sour ce with synchr onous rectifier 10 ______________________________________________________________________________________ p n d1 d0 t i/0 i/0 ch1 ch0 pdrv ndrv pgnd cs+ cs- r3 r4 term gnd low-side is shorted dc in r sense MAX1640 batt figure 5. microcontroller battery charger
configuration to pgnd. these traces should be wide to reduce resistance and as short as possible to reduce stray inductance. all low-current ground paths should be connected to gnd. place the input bypass capaci- tor as close as possible to the in pin. see MAX1640 ev kit for layout example. MAX1640/max1641 adjustable-output, switch-mode current source with synchronous rectifier ___________________ chip infor mation transistor count: 1233 qsop.eps maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 _____________________ 11 ? 2002 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .)

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