1 ltc1731-4.2 lithium-ion linear battery charger controller june 2000 the ltc ? 1731-4.2 is a complete constant-current/con- stant-voltage linear charger controller for lithium-ion batteries. nickel-cadmium (nicd) and nickel-metal-hy- dride (nimh) batteries can also be charged with constant current using external termination. the external sense resistor sets the charge current with 5% accuracy. an internal resistor divider and precision reference set the final float potential with 1% accuracy. the output float voltage is set internally to 4.2v. when the input supply is removed, the ltc1731-4.2 automatically enters a low current sleep mode, dropping the battery drain current to typically 7 m a. an internal comparator detects the end-of-charge ( c /10) condition while a programmable timer, using an external capacitor, sets the total charge time. fully discharged cells are automatically trickle charged at 10% of the programmed current until cell voltage exceeds 2.457v. the ltc1731-4.2 is available in the 8-pin msop and so packages. n complete linear charger controller for 1-cell lithium-ion batteries n 1% voltage accuracy n programmable charge current n c/10 charge current detection output n programmable charge termination timer n space saving 8-pin msop package n automatic sleep mode when input supply is removed (7 m a battery drain) n automatic trickle charging of low voltage cells n programmable for constant-current-only mode n cellular phones n handheld computers n charging docks and cradles n programmable current source , ltc and lt are registered trademarks of linear technology corporation. features descriptio n u applicatio n s u typical applicatio n u v cc v in 5v to 12v sense drv 1k r sense 0.2 r prog * 19.6k li-ion cell ltc1731-4.2 *shutdown invoked by floating the prog pin bat chrg 8 7 mbrm120t3 10 f 1731 ta01 1 f i bat = 500ma c timer 0.1 f charge status q1 si9430dy 6 1 5 4 + 2 3 timer prog gnd 500ma li-ion battery charger information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. final electrical specifications
2 ltc1731-4.2 symbol parameter conditions min typ max units v cc input supply voltage l 4.5 12 v i cc input supply current charger on, current mode l 13 ma shutdown mode l 12 ma sleep mode (battery drain current) 7 20 m a v bat regulated output voltage ltc1731-4.2 (5v v cc 12v) l 4.158 4.2 4.242 v i bat current mode charge current r prog = 19.6k, r sense = 0.2 w 465 500 535 ma r prog = 19.6k, r sense = 0.2 w l 415 585 ma r prog = 97.6k, r sense = 0.2 w 70 100 130 ma i trikl trickle charge current v bat = 2v, r prog = 19.6k, i trikl = (v cc C v sense )/0.2 w l 30 50 100 ma v trikl trickle charge threshold voltage from low to high l 2.35 2.457 2.55 v v uv v cc undervoltage lockout voltage from low to high l 4.1 4.5 v d v uv v cc undervoltage lockout hysteresis 200 mv v msd manual shutdown threshold voltage prog pin low to high 2.457 v prog pin high to low 2.446 v order part number (note 1) input supply voltage (v cc ) ................................... 13.2v input voltage (sense, drv, bat, timer, prog) .................................. C 0.3v to 13.2v output voltage (chrg) ......................... C 0.3v to 13.2v ltc1731ems8-4.2 t jmax = 150 c, q ja = 180 c/w consult factory for industrial and military grade parts. absolute m axi m u m ratings w ww u package/order i n for m atio n w u u operating temperature range (note 2) .....C 40 to 85 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c ms8 part marking ltkq 1 2 3 4 bat chrg timer gnd 8 7 6 5 sense v cc drv prog top view ms8 package 8-lead plastic msop order part number ltc1731es8-4.2 s8 part marking 173142 the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v cc = 6v unless otherwise noted. electrical characteristics 1 2 3 4 8 7 6 5 top view sense v cc drv prog bat chrg timer gnd s8 package 8-lead plastic so t jmax = 150 c, q ja = 125 c/w
3 ltc1731-4.2 note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. symbol parameter conditions min typ max units v asd automatic shutdown threshold voltage (v cc C v bat ) high to low 30 54 90 mv (v cc C v bat ) low to high 40 69 100 mv v dis voltage mode disable threshold voltage v dis = v cc C v timer l 0.4 v i prog prog pin current internal pull-up current, no r prog 2.5 m a prog pin load regulation prog pin source current, d v prog 5mv l 300 m a v prog prog pin voltage r prog =19.6k 2.457 v i chrg chrg pin weak pull-down current v chrg = 1v 50 100 150 m a v chrg chrg pin output low voltage i chrg = 5ma 0.6 1.2 v i c/10 end of charge indication current level r prog = 19.6k, r sense = 0.2 w l 25 50 100 ma t timer timer accuracy c timer = 0.1 m f10% v clamp drv pin clamp voltage v clamp = v cc C v drv , i drive = 50 m a 6.5 v electrical characteristics pi n fu n ctio n s uuu bat (pin 1): battery sense input. a bypass capacitor of at least 10 m f is required to keep the loop stable when the battery is not connected. a precision internal resistor divider sets the final float potential on this pin. the resistor divider is disconnected in sleep mode. chrg (pin 2): open-drain charge status output. when the battery is being charged, the chrg pin is pulled low by an internal n-channel mosfet. when the charge current drops to 10% of the full-scale current for at least 0.32 seconds, the n-channel mosfet turns off and a 100 m a current source is connected from the chrg pin to gnd. when the timer runs out or the input supply is removed, the current source will be disconnected and the chrg pin is forced into a high impedance state. timer (pin 3): timer capacitor and constant-voltage mode disable input pin. the timer period is set by placing a capacitor, c timer , to gnd. the timer period is t timer = (c timer ? 3 hours)/(0.1 m f). when the timer pin is connected to v cc , the constant-voltage mode is disabled and the chip will operate in constant-current mode only. short the timer pin to gnd to disable the internal timer function. gnd (pin 4): ground. prog (pin 5): charge current program and shutdown input pin. the charge current is programmed by connect- ing a resistor, r prog to ground. the charge current is i bat = (v prog ? 800 w )/(r prog ? r sense ). the ic can be forced into shutdown by either floating the prog pin or pulling it up to v cc . an internal 2.5 m a current source will pull the pin above the shutdown threshold voltage when the program resistor (r prog ) is disconnected. drv (pin 6): drive output pin for the p-channel mosfet or pnp transistor. the impedance is high at this pin, therefore, a high gain pnp pass transistor should be used. the drv pin is internally clamped to 6.5v below v cc . v cc (pin 7): positive input supply voltage. when v bat is within 54mv of v cc , the ltc1731-4.2 is forced into sleep mode, dropping i cc to 7 m a. v cc ranges from 4.5v to 12v. bypass this pin with a 1 m f capacitor. sense (pin 8): current sense input. a sense resistor, r sense , must be connected from v cc to the sense pin. this resistor is chosen using the following equation: r sense = (v prog ? 800 w )/(r prog ? i bat ) note 2: the ltc1731-4.2 is guaranteed to meet performance specifications from 0 c to 70 c. specifications over the C 40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical process controls. guaranteed i grade parts are available, consult factory. the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v cc = 6v unless otherwise noted.
4 ltc1731-4.2 block diagra w + + + + logic c1 + c4 + + c3 a1 ca c2 va charge gnd 1731 bd prog battery current i bat = (2.457v ?800 )/(r prog ?r sense ) r prog v ref 2.457v lbo 80 v cc 800 54mv r sense sense drv bat 720 100 a timer oscillator v ref counter stop shdn slp c /10 c /10 2.5 a v cc chrg 4 5 2 3 8 7 6 1 +
5 ltc1731-4.2 operatio u the ltc1731-4.2 is a linear battery charger controller. the charge current is programmed by the combination of a program resistor (r prog ) from the prog pin to ground and a sense resistor (r sense ) between the v cc and sense pins. r prog sets a program current through an internal trimmed 800 w resistor setting up a voltage drop from v cc to the input of the current amplifier (ca). the current amplifier servos the gate of the external p-channel mosfet to force the same voltage drop across r sense which sets the charge current. when the potential at the bat pin approaches the preset float voltage, the voltage amplifier (va) will start sinking current which shrinks the voltage drop across r sense , thus reducing the charge current. charging begins when the potential at v cc pin rises above the uvlo level and a program resistor is connected from the prog pin to ground. at the beginning of the charge cycle, if the battery voltage is below 2.457v, the charger goes into trickle charge mode. the trickle charge current is 10% of the full-scale current. if the cell voltage stays low for one quarter of the total charge time, the charge sequence will be terminated. the charger goes into the fast charge constant-current mode after the voltage on the bat pin rises above 2.457v. in constant-current mode, the charge current is set by the combination of r sense and r prog . when the battery approaches the final float voltage, the charge current will begin to decrease. when the current drops to 10% of the full-scale charge current, an internal comparator will turn off the pull-down n-channel mosfet at the chrg pin and connect a weak current source to ground to indicate an end-of-charge ( c /10) condition. an external capacitor on the timer pin sets the total charge time. after a time-out occurs, the charging will be terminated and the chrg pin is forced to a high imped- ance state. to restart the charge cycle, simply remove the input voltage and reapply it, or float the prog pin momentarily. for batteries like lithium-ion that require accurate final float potential, the internal 2.457v reference, voltage amplifier and the resistor divider provide regulation with 1% (max) accuracy. for nimh and nicd batteries, the ltc1731-4.2 can be turned into a current source by pulling the timer pin to v cc . when in the constant- current only mode, the voltage amplifier, timer and the trickle charge function are all disabled. when the input voltage is not present, the charger goes into a sleep mode, dropping i cc to 7 m a. this greatly reduces the current drain on the battery and increases the standby time. the charger can be shut down by floating the prog pin. an internal current source will pull it high and clamp at 3.5v. applicatio n s i n for m atio n wu u u charge termination the charger is off when any of the following conditions exist: the voltage at the v cc pin is below 4.1v, the voltage at the v cc pin is higher than 4.1v but is less than 54mv above v bat , or the prog pin is floating. the drv pin will be pulled to v cc and the internal resistor divider is discon- nected to reduce the current drain on the battery. undervoltage lockout (uvlo) an internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until v cc rises above 4.1v. to prevent oscillation around v cc = 4.1v, the uvlo circuit has built-in hysteresis. trickle charge and defective battery detection at the beginning of the charging sequence, if the battery voltage is low (below 2.457v) the charger goes into trickle charge mode. the charge current is set to 10% of the full- scale current. if the low cell voltage persists for one quarter of the total charging time, the battery is considered defective, charging will be terminated and the chrg pin output is forced to a high impedance state. shutdown the ltc1731-4.2 can be forced into shutdown by float- ing the prog pin and allowing the internal 2.5 m a current source to pull the pin above the 2.457v shutdown
6 ltc1731-4.2 threshold voltage. the drv pin will then be pulled up to v cc and turn off the external p-channel mosfet. the internal timer is reset in the shutdown mode. programming charge current the formula for the battery charge current (see block diagram) is: i bat = (i prog )(800 w /r sense ) = (2.457v/r prog )(800 w /r sense ) where r prog is the total resistance from the prog pin to ground. for example, if 0.5a charge current is needed, select a value for r sense that will drop 100mv at the maximum charge current. r sense = 0.1v/0.5a = 0.2 w , then calculate: r prog = (2.457v/500ma)(800 w /0.2 w ) = 19.656k for best stability over temperature and time, 1% resistors are recommended. the closest 1% resistor value is 19.6k. programming the timer the programmable timer is used to terminate the charge. the length of the timer is programmed by an external capacitor at the timer pin. the total charge time is: time = (3 hours)(c timer /0.1 m f) the timer starts when the input voltage greater than 4.1v is applied and the program resistor is connected to ground. after a time-out occurs, the chrg output will turn into a high impedance state to indicate that the charging has stopped. connecting the timer pin to v cc disables the timer and also puts the charger into a constant-current mode. to only disable the timer function, short the timer pin to gnd. chrg status output pin when the charge cycle starts, the chrg pin is pulled down to ground by an internal n-channel mosfet that can drive an led. when the battery current drops to 10% of the full- scale current ( c /10), the n-channel mosfet is turned off and a weak 100 m a current source to ground is connected to the chrg pin. after a time-out occurs, the pin will go into a high impedance state. by using two different value pull-up resistors, a microprocessor can detect three states applicatio n s i n for m atio n wu u u from this pin (charging, c /10 and stop charging). see figure 1. when the ltc1731-4.2 is in charge mode, the chrg pin is pulled down by an internal n-channel mosfet. to de- tect this mode, force the digital output pin, out, high and measure the voltage at the chrg pin. the n-channel mosfet will pull the pin low even with a 1k pull-up resis- tor. once the charge current drops to 10% of the full-scale current ( c /10), the n-channel mosfet is turned off and a 100 m a current source is connected to the chrg pin. the in pin will then be pulled high by the 1k pull-up. by forcing the out pin into a high impedance state, the current source will pull the pin low through the 100k resistor. when the internal timer has expired, the chrg pin will change to high impedance state and the 100k resistor will then pull the pin high to indicate the charging has stopped. end of charge (c/10) the ltc1731-4.2 includes a comparator to monitor the charge current to detect an end-of-charge condition. when the battery current falls below 10% of full scale, the comparator trips and turns off the n-channel mosfet at the chrg pin and switches in a 100 m a current source to ground. after an internal time delay of 300ms, this state is then latched. this delay will help prevent false triggering due to transient currents. the end-of-charge comparator is disabled in trickle charge mode. gate drive typically the ltc1731-4.2 controls an external p-channel mosfet to supply current to the battery. the drv pin is internally clamped to 6.5v below v cc . this feature allows low voltage p-channel mosfets with gate to source breakdown voltage rated at 8v to be used. 1k 100k chrg 1731 f01 v cc ltc1731-4.2 v + v dd out processor in 2 7 figure 1. microprocessor interface
7 ltc1731-4.2 an external pnp transistor can also be used as the pass transistor instead of the p-channel mosfet. due to the low current gain of the current amplifier (ca), a high gain darlington pnp transistor is required to avoid excessive charge current error. the gain of the current amplifier is around 0.6 m a/mv. for every 1 m a of base current, a 1.6mv of gain error shows up at the inputs of ca. with r prog = 19.6k (100mv across r sense ), it represents 1.67% of error in charging current. constant-current only mode the ltc1731-4.2 can be used as a programmable current source by forcing the timer pin to v cc . this is particularly useful for charging nimh or nicd batteries. in the con- stant-current only mode, the timer and voltage amplifier applicatio n s i n for m atio n wu u u are both disabled. an external termination method is required to properly terminate the charge. stability the charger is stable without any compensation when a p-channel mosfet is used as the pass transistor. however, a 10 m f capacitor is recommended at the bat pin to keep the ripple voltage low when the battery is disconnected. when a pnp transistor is chosen as the pass transistor, a 1000pf capacitor is required from the drv pin to v cc . this capacitor is needed to help stablize the voltage loop. a 10 m f capacitor at the bat pin is also recommended when a battery is not present. dimensions in inches (millimeters) unless otherwise noted. package descriptio n u s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 0.016 ?0.050 (0.406 ?1.270) 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) so8 1298 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) typ 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** ms8 package 8-lead plastic msop (ltc dwg # 05-08-1660) msop (ms8) 1098 * dimension does not include mold flash, protrusions or gate burrs. mold flash, protrusions or gate burrs shall not exceed 0.006" (0.152mm) per side ** dimension does not include interlead flash or protrusions. interlead flash or protrusions shall not exceed 0.006" (0.152mm) per side 0.021 0.006 (0.53 0.015) 0 ?6 typ seating plane 0.007 (0.18) 0.040 0.006 (1.02 0.15) 0.012 (0.30) ref 0.006 0.004 (0.15 0.102) 0.034 0.004 (0.86 0.102) 0.0256 (0.65) bsc 12 3 4 0.193 0.006 (4.90 0.15) 8 7 6 5 0.118 0.004* (3.00 0.102) 0.118 0.004** (3.00 0.102)
8 ltc1731-4.2 1731ia lt/tp 0600 2k rev a ? printed in usa part number description comments lt ? 1510-5 500khz constant-voltage/constant-current most compact, up to 1.5a, charges nicd, nimh, li-ion cells battery charger lt1512 sepic battery charger v in can be higher or lower than battery voltage, 1.5a switch lt1571-1/lt1571-2 200khz/500khz constant-current/constant-voltage up to 1.5a charge current for 1- or 2-cell li-ion batteries, pr eset and lt1571-5 battery charger family adjustable battery voltages, c /10 charge detection lt1620/lt1621 rail-to-rail current sense amplifier precise output current programming, up to 32v v out ltc1729 termination controller for li-ion time or charge current termination, automatic charger/battery detection, status output, preconditioning, 8-lead msop ltc1731-8.4 li-ion linear battery charger 2-cell li-ion charger, c /10 detection, complete charger related parts 1.5a single cell switching battery charger v cc sense drv r5 1k r3 0.082 1/4w r2 4.7 1-cell li-ion battery r4 18.2k 1% + ltc1731-4.2 bat chrg 8 7 c3 100 f 1731 ta03 c2 22 f cer c1* 0.1 f q2 si2305ds d1 mbrs130lt3 22 h cdrh6d38-220nc d2 mbrs130lt3 v in 5v to 6v 6 4 2 5 3 tps2829dbvr 1 *avx 0603zc104kat1a 45 2 3 timer gnd prog c4 0.47 f c5 1 f cer + linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com ? linear technology corporation 1999 v cc v in 5v to 12v sense drv r2 1k r sense 0.2 r1 10k r prog 19.6k li-ion cell ltc1731-4.2 bat chrg 8 7 mbrm120t3 c2 10 f c1 1nf 1731 ta02 c3 1 f i bat = 500ma + c timer 0.1 f q1 2n5087 6 1 5 4 2 3 timer prog gnd q2 ztx749 linear charger using a pnp transistor typical applicatio s u v cc v in 5v sense drv 4.7k 1k 2.2k 1k amber 1.5k 20k r sense 0.2 r prog 19.6k li-ion cell ltc1731-4.2 bat chrg 8 7 10 f 1731 ta04 0.1 f si9430dy 6 1 5 4 + 2 3 timer prog gnd green mmbt3906 mmsd4148 mbrm120t3 optional: for reverse input protection mmbt3906 condition no wall adapter charging (i > c /10) charging (i < c /10) timer expired green off off on on amber off on off off using chrg pin to indicate charge status
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