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1 lt1510/lt1510-5 constant-voltage/ constant-current battery charger figure 2. charging lithium batteries (efficiency at 1.3a > 87%) * nicd and nimh batteries require charge termination circuitry (not shown in figure 1). typical applicatio n s u , ltc and lt are registered trademarks of linear technology corporation. plest, most efficient solution to fast-charge modern re- chargeable batteries including lithium-ion (li-ion), nickel- metal-hydride (nimh)* and nickel-cadmium (nicd)* that require constant-current and/or constant-voltage charg- ing. the internal switch is capable of delivering 1.5a dc current (2a peak current). the 0.1 w onboard current sense resistor makes the charging current programming very simple. one resistor (or a programming current from a dac) is required to set the full charging current (1.5a) to within 5% accuracy. the lt1510 with 0.5% reference voltage accuracy meets the critical constant-voltage charg- ing requirement for lithium cells. the lt1510 can charge batteries ranging from 2v to 20v. ground sensing of current is not required and the batterys negative terminal can be tied directly to ground. a saturat- ing switch running at 200khz (500khz for lt1510-5) gives high charging efficiency and small inductor size. a block- ing diode is not required between the chip and the battery because the chip goes into sleep mode and drains only 3 m a when the wall adaptor is unplugged. soft start and shutdown features are also provided. the lt1510 is available in a 16-pin fused lead power so package with a thermal resistance of 50 c/w, an 8-pin so and a 16-pin pdip. features n charges nicd, nimh and lithium-ion batteries CC only one 1 / 10 w resistor is needed to program charging current n high efficiency current mode pwm with 1.5a internal switch and sense resistor n 3% typical charging current accuracy n precision 0.5% voltage reference for voltage mode charging or overvoltage protection n current sensing can be at either terminal of the battery n low reverse battery drain current: 3 m a n charging current soft start n shutdown control n 500khz version uses small inductor with switching frequency as high as 500khz, the lt ? 1510 current mode pwm battery charger is the smallest, sim- applicatio n s u descriptio n u n chargers for nicd, nimh and lithium batteries n step-down switching regulator with precision adjustable current limit figure 1. 500khz smallest li-ion cell phone charger (0.8a) sw boost gnd sense v cc prog v c bat 6.19k 8.2v to 20v + r3 70.6k 0.25% r4 100k 0.25% q3 ? 2n7002 note: complete lithium-ion charger, no termination required tokin or marcon ceramic surface mount coiltronics tp3-100, 10 h, 2.2mm height (0.8a charging current) coiltronics tp1 series, 10 h, 1.8mm height (<0.5a charging current) panasonic eefcd1b220 optional, see applications information 1510 f01 c1 0.22 m f c in * 10 m f l1** 10 m h lt1510-5 d1 mbrm120t3 d3 mbrm120t3 d2 mmbd914l ovp + c out *** 22 m f 4.2v + + 0.1 m f 1k 1 m f 300 w * ** *** ? sw boost gnd sense v cc prog v c bat 3.83k 11v to 28v + + r3 240k 0.25% r4 100k 0.25% q3 ? vn2222 note: complete lithium-ion charger, no termination required * tokin or marcon ceramic surface mount ** coiltronics ctx33-2 ? optional, see applications information 1510 f02 c1 0.22 m f c in * 10 m f l1** 33 m h lt1510 d1 1n5819 d3 1n5819 d2 1n914 ovp + c out 22 m f tant 4.2v 4.2v + + 0.1 m f 1k 1 m f 300 w
2 lt1510/lt1510-5 supply voltage (v max ) ............................................ 30v switch voltage with respect to gnd ...................... C 3v boost pin voltage with respect to v cc ................... 30v boost pin voltage with respect to gnd ................. C 5v v c , prog, ovp pin voltage ...................................... 8v i bat (average) ........................................................ 1.5a switch current (peak)............................................... 2a storage temperature range ................. C 65 c to 150 c absolute m axi m u m ratings w ww u operating ambient temperature range commercial ............................................. 0 c to 70 c extended commercial (note 7) ........... C 40 c to 85 c industrial (note 8) .............................. C 40 c to 85 c operating junction temperature range lt1510c (note 7) ............................. C 40 c to 125 c lt1510i ............................................ C 40 c to 125 c lead temperature (soldering, 10 sec).................. 300 c package/order i n for m atio n w u u consult factory for military grade parts. electrical characteristics v cc = 16v, v bat = 8v, v max (maximum operating v cc ) = 28v, no load on any outputs, unless otherwise noted. (notes 7, 8) parameter conditions min typ max units overall supply current v prog = 2.7v, v cc 20v l 2.90 4.3 ma v prog = 2.7v, 20v < v cc v max l 2.91 4.5 ma dc battery current, i bat (note 1) 8v v cc 25v, 0v v bat 20v, t j < 0 c l 0.91 1.09 a r prog = 4.93k l 0.93 1.0 1.07 a r prog = 3.28k (note 4) l 1.35 1.5 1.65 a r prog = 49.3k l 75 100 125 ma t j < 0 c l 70 130 ma v cc = 28v, v bat = 20v r prog = 4.93k l 0.93 1.0 1.07 a r prog = 49.3k l 75 100 125 ma lt1510cn lt1510cs lt1510in lt1510is order part number t jmax = 125 c, q ja = 125 c/ w order part number gn part marking *v cc1 and v cc2 should be connected together close to the pins. ** four corner pins are fused to internal die attach paddle for heat sinking. connect these four pins to expanded pc lands for proper heat sinking. 1 2 3 4 5 6 7 8 top view n package 16-lead pdip 16 15 14 13 12 11 10 9 **gnd sw boost gnd ovp sense gnd **gnd gnd** v cc2 v cc1 prog v c bat gnd gnd** s package* 16-lead plastic so t jmax = 125 c, q ja = 75 c/ w (n) t jmax = 125 c, q ja = 50 c/ w (s)* 1 2 3 4 8 7 6 5 top view sw boost gnd sense v cc prog v c bat s8 package 8-lead plastic so lt1510cs8 lt1510is8 1510 1510i order part number s8 part marking 1 2 3 4 5 6 7 8 top view 16 15 14 13 12 11 10 9 **gnd sw boost gnd ovp nc sense **gnd gnd** v cc2 v cc1 prog v c nc bat gnd** gn package (0.015 in) 16-lead plastic ssop t jmax = 125 c, q ja = 75 c/ w ** four corner pins are fused to internal die attach paddle for heat sinking. connect these four pins to expanded pc lands for proper heat sinking. lt1510cgn lt1510ign lt1510-5cgn lt1510-5ign 1510 1510i 15105 15105i
3 lt1510/lt1510-5 electrical characteristics v cc = 16v, v bat = 8v, v max (maximum operating v cc ) = 28v, no load on any outputs, unless otherwise noted. parameter conditions min typ max units overall minimum input operating voltage undervoltage lockout l 6.2 7 7.8 v reverse current from battery (when v cc is not v bat 20v, 0 c t j 70 c l 315 m a connected, v sw is floating) boost pin current v cc C v boost 20v l 0.10 20 m a 20v < v cc C v boost 28v l 0.25 30 m a 2v v boost C v cc 8v (switch on) l 611 ma 8v < v boost C v cc 25v (switch on) l 814 ma switch switch on resistance v cc = 10v i sw = 1.5a, v boost C v sw 3 2v (note 4) l 0.3 0.5 w i sw = 1a, v boost C v sw < 2v (unboosted) l 2.0 w d i boost / d i sw during switch on v boost = 24v, i sw 1a 20 35 ma/a switch off leakage current v sw = 0v, v cc 20v l 2 100 m a 20v < v cc 28v l 4 200 m a maximum v bat with switch on l v cc C 2 v minimum i prog for switch on 2420 m a minimum i prog for switch off at v prog 1v l 1 2.4 ma current sense amplifier inputs (sense, bat) sense resistance (r s1 ) 0.08 0.12 w total resistance from sense to bat (note 3) 0.2 0.25 w bat bias current (note 5) v c < 0.3v C 200 C 375 m a v c > 0.6v 700 1300 m a input common mode limit (low) l C 0.25 v input common mode limit (high) l v cc C 2 v reference reference voltage (note 1) s8 package r prog = 4.93k, measured at prog pin l 2.415 2.465 2.515 v reference voltage (note 2) 16-pin r prog = 3.28k, measured at ovp with 2.453 2.465 2.477 v va supplying i prog and switch off reference voltage tolerance, 16-pin only 8v v cc 28v, 0 c t j 70 c l 2.446 2.465 2.480 v 8v v cc 28v, 0 c t j 125 c l 2.441 2.489 v 8v v cc 28v, t j < 0 c l 2.430 2.489 v oscillator switching frequency lt1510 180 200 220 khz lt1510-5 440 500 550 khz switching frequency tolerance all conditions of v cc , temperature, lt1510 l 170 200 230 khz lt1510, t j < 0 c l 160 230 khz lt1510-5 l 425 500 575 khz lt1510-5, t j < 0 c l 400 575 khz maximum duty cycle lt1510 l 87 % lt1510, t a = 25 c (note 8) 90 93 % lt1510-5 (note 9) l 77 81 %
4 lt1510/lt1510-5 electrical characteristics v cc = 16v, v bat = 8v, v max (maximum operating v cc ) = 28v, no load on any outputs, unless otherwise noted. parameter conditions min typ max units current amplifier (ca2) transconductance v c = 1v, i vc = 1 m a 150 250 550 m mho maximum v c for switch off l 0.6 v i vc current (out of pin) v c 3 0.6v 100 m a v c < 0.45v 3 ma voltage amplifier (va), 16-pin only transconductance (note 2) output current from 100 m a to 500 m a 0.5 1.2 2.5 mho output source current, v cc = 10v v prog = v ovp = v ref + 10mv 1.3 ma ovp input bias current at 0.75ma va output current l 50 150 na the l denotes specifications which apply over the specified temperature range. note 1: tested with test circuit 1. note 2: tested with test circuit 2. note 3: sense resistor r s1 and package bond wires. note 4: applies to 16-pin only. 8-pin packages are guaranteed but not tested at C 40 c. note 5: current ( ? 700 m a) flows into the pins during normal operation and also when an external shutdown signal on the v c pin is greater than 0.3v. current decreases to ? 200 m a and flows out of the pins when external shutdown holds the v c pin below 0.3v. current drops to near zero when input voltage collapses. see external shutdown in applications information section. note 6: a linear interpolation can be used for reference voltage specification between 0 c and C 40 c. note 7: commercial grade device specifications are guaranteed over the 0 c to 70 c temperature range. in addition, commercial grade device specifications are assured over the C40 c to 85 c temperature range by design or correlation, but are not production tested. maximum allowable ambient temperature may be limited by power dissipation. parts may not necessarily be operated simultaneously at maximum power dissipation and maximum ambient temperature. temperature rise calculations must be done as shown in the applications information section to ensure that maximum junction temperature does not exceed the 125 c limit. with high power dissipation, maximum ambient temperature may be less than 70 c. note 8: industrial grade device specifications are guaranteed over the C40 c to 85 c temperature range. note 9: 91% maximum duty cycle is guaranteed by design if v bat or v x (see figure 8 in application information) is kept between 3v and 5v. note 10: v bat = 4.2v. thermally limited maximum charging current, 8-pin so input voltage (v) 0 maximum charging current (a) 1.3 1.1 0.9 0.7 0.5 0.3 20 1510 g12 5 10 15 25 16v battery 12v battery 8v battery 4v battery ( q ja =125 c/w) t amax =60 c t jmax =125 c thermally limited maximum charging current, 16-pin so input voltage (v) 0 maximum charging current (a) 1.5 1.3 1.1 0.9 0.7 0.5 20 1510 g13 5 10 15 25 ( q ja =50 c/w) t amax =60 c t jmax =125 c 16v battery 12v battery 8v battery 4v battery thermally limited maximum charging current, 16-pin gn input voltage (v) 0 maximum charging current (a) 1.5 1.3 1.1 0.9 0.7 0.5 20 lt1510 ?tpc14 5 10 15 25 q ja = 80 c/w t amax = 60 c t jmax = 125 c 4v battery 8v battery 12v battery 16v battery typical perfor m a n ce characteristics u w
5 lt1510/lt1510-5 typical perfor m a n ce characteristics u w switching frequency vs temperature duty cycle (%) 010305070 i cc (ma) 80 1510 g04 20 40 60 8 7 6 5 4 3 2 1 0 125 c 0 c 25 c v cc = 16v i cc vs duty cycle temperature ( c) ?0 frequency (khz) 20 0 40 80 120 60 100 140 1510 g05 210 205 200 195 190 185 180 i bat (a) 0.1 efficiency (%) 100 98 96 94 92 90 88 86 84 82 80 0.5 0.9 1.5 1.3 1.1 1510 g01 0.3 0.7 v cc = 15v (excluding dissipation on input diode d3) v bat = 8.4v efficiency of figure 2 circuit i cc vs v cc v cc (v) 0 i cc (ma) 7.0 6.5 6.0 5.5 5.0 4.5 5 10 15 20 1510 g03 25 30 125 c 25 c 0 c maximum duty cycle i va (ma) 0 ? v ovp (mv) 4 3 2 1 0 0.8 1510 g08 0.2 0.1 0.3 0.5 0.7 0.9 0.4 0.6 1.0 125 c 25 c i va vs d v ovp (voltage amplifier) v cc (v) 0 ? v ref (v) 0.003 0.002 0.001 0 0.001 0.002 0.003 5 10 15 20 1510 g02 25 30 all temperatures v ref line regulation temperature ( c) 0 duty cycle (%) 120 1510 g09 40 80 98 97 96 95 94 93 92 91 90 20 60 100 140 maximum duty cycle v prog (v) 0123 5 4 i prog (ma) 6 0 ? 1510 g11 125 c 25 c prog pin characteristic v c (v) 0 0.2 0.6 1.0 1.4 1.8 i vc (ma) 1.20 1.08 0.96 0.84 0.72 0.60 0.48 0.36 0.24 0.12 0 0.12 1.6 1510 g10 0.4 0.8 1.2 2.0 v c pin characteristic
6 lt1510/lt1510-5 typical perfor m a n ce characteristics u w switch current (a) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.8 2.0 1.6 boost current (ma) 50 45 40 35 30 25 20 15 10 5 0 1510 g07 v cc = 16v v boost = 38v 28v 18v switch current vs boost current vs boost voltage temperature ( c) 0 reference voltage (v) 2.470 2.468 2.466 2.464 2.462 2.460 2.458 25 50 75 100 1510 g14 125 150 reference voltage vs temperature v boost (v) 4 268 maximum duty cycle (%) 16 18 20 96 95 94 93 92 91 90 89 88 87 86 lt1510 ?tpc15 10 12 14 22 v boost vs maximum duty cycle pi n fu n ctio n s uuu gnd: ground pin. sw: switch output. the schottky catch diode must be placed with very short lead length in close proximity to sw pin and gnd. v cc : supply for the chip. for good bypass, a low esr capacitor of 10 m f or higher is required, with the lead length kept to a minimum. v cc should be between 8v and 28v and at least 2v higher than v bat for v bat less than 10v, and 2.5v higher than v bat for v bat greater than 10v. under- voltage lockout starts and switching stops when v cc goes below 7v. note that there is a parasitic diode inside from sw pin to v cc pin. do not force v cc below sw by more than 0.7v with battery present. all v cc pins should be shorted together close to the pins. boost: this pin is used to bootstrap and drive the switch power npn transistor to a low on-voltage for low power dissipation. in normal operation, v boost = v cc + v bat when switch is on. maximum allowable v boost is 55v. sense: current amplifier ca1 input. sensing can be at either terminal of the battery. note that current sense resistor r s1 (0.08 w ) is between sense and bat pins. bat: current amplifier ca1 input. prog: this pin is for programming the charging current and for system loop compensation. during normal opera- tion, v prog stays close to 2.465v. if it is shorted to gnd the switching will stop. when a microprocessor-controlled dac is used to program charging current, it must be capable of sinking current at a compliance up to 2.465v. v c : this is the control signal of the inner loop of the current mode pwm. switching starts at 0.7v and higher v c corresponds to higher charging current in normal opera- tion. a capacitor of at least 0.1 m f to gnd filters out noise and controls the rate of soft start. to shut down switching, pull this pin low. typical output current is 30 m a. ovp: this is the input to the amplifier va with a threshold of 2.465v. typical input current is about 50na into pin. for charging lithium-ion batteries, va monitors the battery voltage and reduces charging current when battery volt- age reaches the preset value. if it is not used, the ovp pin should be grounded.
7 lt1510/lt1510-5 block diagra m w test circuits test circuit 1 + v ref ? 0.65v v bat v c 2n3055 1k lt1010 ca2 + + ca1 + + 3.3k 20k 1k 1k r s1 i bat bat sense 1510 tc01 prog r prog 0.047 m f lt1510 0.22 m f 56 m f 60k lt1006 + + + + + + v sw 0.7v 1.5v v bat v ref v c gnd slope compensation r2 r3 c1 pwm b1 ca2 + + ca1 va + + v ref 2.465v shutdown 200khz oscillator s r r r1 1k r s1 i bat i prog i prog v cc v cc boost sw sense bat 0vp 1510 bd prog r prog c prog 60k i prog i bat = 500 m a/a q sw g m = 0.64 w charging current i bat = (i prog )(2000) = 2.465v r prog (2000) ()
8 lt1510/lt1510-5 test circuits v ref 2.465v + + va + 10k 10k ovp 1510 tc02 i prog r prog lt1510 prog lt1013 0.47 m f test circuit 2 operatio u the lt1510 is a current mode pwm step-down (buck) switcher. the battery dc charging current is programmed by a resistor r prog (or a dac output current) at the prog pin (see block diagram). amplifier ca1 converts the charging current through r s1 to a much lower current i prog (500 m a/a) fed into the prog pin. amplifier ca2 compares the output of ca1 with the programmed current and drives the pwm loop to force them to be equal. high dc accuracy is achieved with averaging capacitor c prog . note that i prog has both ac and dc components. i prog goes through r1 and generates a ramp signal that is fed to the pwm control comparator c1 through buffer b1 and level shift resistors r2 and r3, forming the current mode inner loop. the boost pin drives the switch npn q sw into saturation and reduces power loss. for batteries like lithium-ion that require both constant-current and con- stant-voltage charging, the 0.5%, 2.465v reference and the amplifier va reduce the charging current when battery voltage reaches the preset level. for nimh and nicd, va can be used for overvoltage protection. when input volt- age is not present, the charger goes into low current (3 m a typically) sleep mode as input drops down to 0.7v below battery voltage. to shut down the charger, simply pull the v c pin low with a transistor. applicatio n s i n for m atio n wu u u application note 68, the lt1510 design manual, contains more in depth appications examples. input and output capacitors in the chargers in figures 1 and 2 on the first page of this data sheet, the input capacitor c in is assumed to absorb all input switching ripple current in the converter, so it must have adequate ripple current rating. worst-case rms ripple current will be equal to one half of output charging current. actual capacitance value is not critical. solid tantalum capacitors such as the avx tps and sprague 593d series have high ripple current rating in a relatively small surface mount package, but caution must be used when tantalum capacitors are used for input bypass . high input surge currents can be created when the adapter is hot-plugged to the charger and solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. highest possible voltage rating on the capacitor will minimize problems. consult with the manufacturer before use. alternatives include new high
9 lt1510/lt1510-5 applicatio n s i n for m atio n wu u u capacity ceramic capacitor (5 m f to 10 m f) from tokin or united chemi-con/marcon, et al., and the old standby, aluminum electrolytic, which will require more microfarads to achieve adequate ripple rating. os-con can also be used. the output capacitor c out is also assumed to absorb output switching current ripple. the general formula for capacitor current is: i v v v lf rms bat bat cc = () - ? ? ? ? ()() 029 1 1 . for example, with v cc = 16v, v bat = 8.4v, l1 = 30 m h and f = 200khz, i rms = 0.2a. emi considerations usually make it desirable to minimize ripple current in the battery leads, and beads or inductors may be added to increase battery impedance at the 200khz switching frequency. switching ripple current splits be- tween the battery and the output capacitor depending on the esr of the output capacitor and the battery impedance. if the esr of c out is 0.2 w and the battery impedance is raised to 4 w with a bead of inductor, only 5% of the current ripple will flow in the battery. soft start the lt1510 is soft started by the 0.1 m f capacitor on v c pin. on start-up, v c pin voltage will rise quickly to 0.5v, then ramp at a rate set by the internal 45 m a pull-up current and the external capacitor. battery charging current starts ramping up when v c voltage reaches 0.7v and full current is achieved with v c at 1.1v. with a 0.1 m f capacitor, time to reach full charge current is about 3ms and it is assumed that input voltage to the charger will reach full value in less than 3ms. capacitance can be increased up to 0.47 m f if longer input start-up times are needed. in any switching regulator, conventional timer-based soft starting can be defeated if the input voltage rises much slower than the time-out period. this happens because the switching regulators in the battery charger and the com- puter power supply are typically supplying a fixed amount of power to the load. if input voltage comes up slowly compared to the soft start time, the regulators will try to deliver full power to the load when the input voltage is still well below its final value. if the adapter is current limited, it cannot deliver full power at reduced output voltages and the possibility exists for a quasi latch state where the adapter output stays in a current limited state at reduced output voltage. for instance, if maximum charger plus computer load power is 20w, a 24v adapter might be current limited at 1a. if adapter voltage is less than (20w/1a = 20v) when full power is drawn, the adapter voltage will be sucked down by the constant 20w load until it reaches a lower stable state where the switching regulators can no longer supply full load. this situation can be prevented by utilizing undevoltage lockout , set higher than the minimum adapter voltage where full power can be achieved. a fixed undervoltage lockout of 7v is built into the v cc pin. internal lockout is performed by clamping the v c pin low. the v c pin is released from its clamped state when the v cc pin rises above 7v. the charger will start delivering current about 2ms after v c is released, as set by the 0.1 m f at v c pin. higher lockout voltage can be implemented with a zener diode (see figure 3 circuit). figure 3. undervoltage lockout gnd v cc v c v in 1510 f03 lt1510 2k d1 1n4001 v z the lockout voltage will be v in = v z + 1v. for example, for a 24v adapter to start charging at 22v in , choose v z = 21v. when v in is less than 22v, d1 keeps v c low and charger off. charging current programming the basic formula for charging current is (see block diagram): ii v r bat prog prog = ()() = ? ? ? ? () 2000 2 465 2000 .
10 lt1510/lt1510-5 where r prog is the total resistance from prog pin to ground. for example, 1a charging current is needed. r v a k prog = ()() = 2 465 2000 1 493 . . charging current can also be programmed by pulse width modulating i prog with a switch q1 to r prog at a frequency higher than a few khz (figure 4). charging current will be proportional to the duty cycle of the switch with full current at 100% duty cycle. when a microprocessor dac output is used to control charging current, it must be capable of sinking current at a compliance up to 2.5v if connected directly to the prog pin. applicatio n s i n for m atio n wu u u even this low current drain. a 47k resistor from adapter output to ground should be added if q3 is used to ensure that the gate is pulled to ground. with divider current set at 25 m a, r4 = 2.465/25 m a = 100k and, r rv ra k ka k bat 3 4 2 465 2 465 4 0 05 100 8 4 2 465 2 465 100 0 05 240 = () - () + () = - () + () = . .. .. .. mm lithium-ion batteries typically require float voltage accu- racy of 1% to 2%. accuracy of the lt1510 ovp voltage is 0.5% at 25 c and 1% over full temperature. this leads to the possibility that very accurate (0.1%) resistors might be needed for r3 and r4. actually, the temperature of the lt1510 will rarely exceed 50 c in float mode because charging currents have tapered off to a low level, so 0.25% resistors will normally provide the required level of overall accuracy. external shutdown the lt1510 can be externally shut down by pulling the v c pin low with an open drain mosfet, such as vn2222. the v c pin should be pulled below 0.8v at room temperature to ensure shutdown. this threshold decreases at about 2mv/ c. a diode connected between the mosfet drain and the v c pin will still ensure the shutdown state over all temperatures, but it results in slightly different conditions as outlined below. if the v c pin is held below threshold, but above ? 0.4v, the current flowing into the bat pin will remain at about 700 m a. pulling the v c pin below 0.4v will cause the current to drop to ? 200 m a and reverse, flowing out of the bat pin. although these currents are low, the long term effect may need to be considered if the charger is held in a shutdown state for very long periods of time, with the charger input voltage remaining. removing the charger input voltage causes all currents to drop to near zero. if it is acceptable to have 200 m a flowing into the battery while the charger is in shutdown, simply pull the v c pin directly to ground with the external mosfet. the resistor divider used to sense battery voltage will pull current out figure 4. pwm current programming pwm r prog 4.64k 300 prog c prog 1 f q1 vn2222 5v 0v lt1510 1510 f04 i bat = (dc)(1a) lithium-ion charging the circuit in figure 2 uses the 16-pin lt1510 to charge lithium-ion batteries at a constant 1.3a until battery volt- age reaches a limit set by r3 and r4. the charger will then automatically go into a constant-voltage mode with cur- rent decreasing to zero over time as the battery reaches full charge. this is the normal regimen for lithium-ion charg- ing, with the charger holding the battery at float voltage indefinitely. in this case no external sensing of full charge is needed. current through the r3/r4 divider is set at a compromise value of 25 m a to minimize battery drain when the charger is off and to avoid large errors due to the 50na bias current of the ovp pin. q3 can be added if it is desired to eliminate
11 lt1510/lt1510-5 applicatio n s i n for m atio n wu u u period, after which the lt1510 can be shut down by pulling the v c pin low with an open collector or drain. some external means must be used to detect the need for additional charging if needed, or the charger may be turned on periodically to complete a short float-voltage cycle. current trip level is determined by the battery voltage, r1 through r3, and the internal lt1510 sense resistor ( ? 0.18 w pin-to-pin). d2 generates hysteresis in the trip level to avoid multiple comparator transitions. nickel-cadmium and nickel-metal-hydride charging the circuit in figure 6 uses the 8-pin lt1510 to charge nicd or nimh batteries up to 12v with charging currents of 0.5a when q1 is on and 50ma when q1 is off. of the battery, canceling part or all of the 200 m a. note that if net current is into the battery and the battery is removed, the charger output voltage will float high, to near input voltage. this could be a problem when reinserting the battery, if the resulting output capacitor/battery surge current is high enough to damage either the battery or the capacitor. if net current into the battery must be less than zero in shutdown, there are several options. increasing divider current to 300 m a - 400 m a will ensure that net battery current is less than zero. for long term storage conditions however, the divider may need to be disconnected with a mosfet switch as shown in figures 2 and 5. a second option is to connect a 1n914 diode in series with the mosfet drain. this will limit how far the v c pin will be pulled down, and current ( ? 700 m a) will flow into the bat pin, and therefore out of the battery. this is not usually a problem unless the charger will remain in the shutdown state with input power applied for very long periods of time. removing input power to the charger will cause the bat pin current to drop to near zero, with only the divider current remaining as a small drain on the battery. even that current can be eliminated with a switch as shown in figures 2 and 5. figure 5. disconnecting voltage divider some battery manufacturers recommend termination of constant-voltage float mode after charging current has dropped below a specified level (typically 50ma to 100ma) and a further time-out period of 30 minutes to 90 minutes has elapsed. this may extend the life of the battery, so check with manufacturers for details. the circuit in figure 7 will detect when charging current has dropped below 75ma. this logic signal is used to initiate a time-out figure 6. charging nimh or nicd batteries (efficiency at 0.5a ? 90%) for a 2-level charger, r1 and r2 are found from: i r bat prog = ()( ) 2000 2 465 . r i r ii low hi low 1 2 465 2000 2 2 465 2000 = ()() = ()() - .. all battery chargers with fast-charge rates require some means to detect full charge state in the battery to terminate the high charging current. nicd batteries are typically charged at high current until temperature rise or battery r3 12k r4 4.99k 0.25% r5 220k ovp v in + + 4.2v 4.2v v bat q3 vn2222 lt1510 1510 f05 sw boost gnd sense v cc prog v c bat r2 11k + r1 100k q1 vn2222 * tokin or marcon ceramic surface mount ** coiltronics ctx33-2 wall adapter 1510 f05.5 c1 0.22 m f c in * 10 m f l1** 33 m h lt1510 d1 1n5819 d3 1n5819 d2 1n914 + c out 22 m f tant 0.1 m f + 1k 1 m f 300 w 2v to 20v i bat on: i bat = 0.5a off: i bat = 0.05a
12 lt1510/lt1510-5 applicatio n s i n for m atio n wu u u figure 7. current comparator for initiating float time-out 0.18 w gnd negative edge to timer internal sense resistor 1510 f06 3.3v or 5v adapter output 3 8 7 1 4 2 lt1510 d1 1n4148 c1 0.1 m f bat sense r1* 1.6k r4 470k r3 430k r2 560k lt1011 d2 1n4148 * trip current = r1(v bat ) (r2 + r3)(0.18 w ) + voltage decrease is detected as an indication of near full charge. the charging current is then reduced to a much lower value and maintained as a constant trickle charge. an intermediate top off current may be used for a fixed time period to reduce 100% charge time. nimh batteries are similar in chemistry to nicd but have two differences related to charging. first, the inflection characteristic in battery voltage as full charge is ap- proached is not nearly as pronounced. this makes it more difficult to use dv/dt as an indicator of full charge, and change of temperature is more often used with a tempera- ture sensor in the battery pack. secondly, constant trickle charge may not be recommended. instead, a moderate level of current is used on a pulse basis ( ? 1% to 5% duty cycle) with the time-averaged value substituting for a constant low trickle. thermal calculations if the lt1510 is used for charging currents above 0.4a, a thermal calculation should be done to ensure that junction temperature will not exceed 125 c. power dissipation in the ic is caused by bias and driver current, switch resis- tance, switch transition losses and the current sense resistor. the following equations show that maximum practical charging current for the 8-pin so package (125 c/w thermal resistance) is about 0.8a for an 8.4v battery and 1.1a for a 4.2v battery. this assumes a 60 c maximum ambient temperature. the 16-pin so, with a thermal resistance of 50 c/w, can provide a full 1.5a charging current in many situations. the 16-pin pdip falls between these extremes. graphs are shown in the typical performance characteristics section. p ma v ma v v v ma i p iv v v p irv v tvi f p bias in bat bat in bat driver bat bat bat in sw bat sw bat in ol in bat sense = ()() + () + () + ()() [] = ()( ) + ? ? ? ? () = ()( )( ) + ()()( )() = 35 15 75 0012 1 30 55 0 2 2 2 .. .. .. 18 2 w ()() i bat r sw = switch on resistance ? 0.35 w t ol = effective switch overlap time ? 10ns f = 200khz (500khz for lt1510-5)
13 lt1510/lt1510-5 applicatio n s i n for m atio n wu u u example: v in = 15v, v bat = 8.4v, i bat = 1.2a; pma ma ma w pw bias driver = ()() + () + () + ()() [] = = ()() + ? ? ? ? () = 35 15 15 84 84 15 75 0012 12 017 12 84 1 84 30 55 15 013 2 2 ... . .... .. . . p khz w pw sw sense = ()( )() + ? ? ? ()( )( ) =+= = ()() = - 12 035 84 15 10 10 15 1 2 200 028 004 032 018 12 026 2 9 2 ... . ... .. . total power in the ic is: 0.17 + 0.13 + 0.32+ 0.26 = 0.88w temperature rise will be (0.88w)(50 c/w) = 44 c. this assumes that the lt1510 is properly heat sunk by con- necting the four fused ground pins to the expanded traces and that the pc board has a backside or internal plane for heat spreading. the p driver term can be reduced by connecting the boost diode d2 (see figures 2 and 6 circuits) to a lower system voltage (lower than v bat ) instead of v bat (see figure 8). then, p ivv v v driver bat bat x x in = ()( )() + ? ? ? ? () 1 30 55 for example, v x = 3.3v, p avv v v w driver = ()()() + ? ? ? ? () = 12 84 33 1 33 30 55 15 0 045 ... . . the average i vx required is: p v w v ma driver x == 0 045 33 14 . . total board area becomes an important factor when the area of the board drops below about 20 square inches. the graph in figure 9 shows thermal resistance vs board area for 2-layer and 4-layer boards. note that 4-layer boards have significantly lower thermal resistance, but both types show a rapid increase for reduced board areas. figure 10 shows actual measured lead temperature for chargers operating at full current. battery voltage and input voltage will affect device power dissipation, so the data sheet power calculations must be used to extrapolate these readings to other situations. vias should be used to connect board layers together. planes under the charger area can be cut away from the rest of the board and connected with vias to form both a board area (in 2 ) 0 60 55 50 45 40 35 30 25 15 25 1510 f08 510 20 30 35 thermal resistance ( c/w) s16, measured from air ambient to die using copper lands as shown on data sheet 2-layer board 4-layer board figure 9. lt1510 thermal resistance boost sw sense v x i vx 1510 f07 lt1510 c1 l1 d2 10 m f + figure 8
14 lt1510/lt1510-5 applicatio n s i n for m atio n wu u u board area (in 2 ) 0 90 80 70 60 50 40 30 20 15 25 1510 f09 510 20 30 35 lead temperature ( c) i chrg = 1.3a v in = 16v v bat = 8.4v v boost = v bat t a = 25 c note: peak die temperature will be about 10 c higher than lead temper- ature at 1.3a charging current 2-layer board 4-layer board event of an input short. the body diode of q2 creates the necessary pumping action to keep the gate of q1 low during normal operation (see figure 11). figure 12. high speed switching path 1510 f12 v bat l1 v in high frequency circulating path bat switch node c in c out figure 10. lt1510 lead temperature low thermal resistance system and to act as a ground plane for reduced emi. higher duty cycle for the lt1510 battery charger maximum duty cycle for the lt1510 is typically 90% but this may be too low for some applications. for example, if an 18v 3% adapter is used to charge ten nimh cells, the charger must put out 15v maximum. a total of 1.6v is lost in the input diode, switch resistance, inductor resistance and parasitics so the required duty cycle is 15/16.4 = 91.4%. as it turns out, duty cycle can be extended to 93% by restricting boost voltage to 5v instead of using v bat as is normally done. this lower boost voltage v x (see figure 8) also reduces power dissipation in the lt1510, so it is a win-win decision. even lower dropout for even lower dropout and/or reducing heat on the board, the input diode d3 (figures 2 and 6) should be replaced with a fet. it is pretty straightforward to connect a p-channel fet across the input diode and connect its gate to the battery so that the fet commutates off when the input goes low. the problem is that the gate must be pumped low so that the fet is fully turned on even when the input is only a volt or two above the battery voltage. also there is a turn off speed issue. the fet should turn off instantly when the input is dead shorted to avoid large current surges form the battery back through the charger into the fet. gate capacitance slows turn off, so a small p-fet (q2) discharges the gate capacitance quickly in the figure 11. replacing the input diode v x 3v to 6v high duty cycle connection v in 1510 f10 c3 l1 d2 d1 q2 q1 r x 50k q1: si4435dy q2: tp0610l c x 10 m f v bat boost sw sense v cc lt1510 bat + + layout considerations switch rise and fall times are under 10ns for maximum efficiency. to prevent radiation, the catch diode, sw pin and input bypass capacitor leads should be kept as short as possible. a ground plane should be used under the switching circuitry to prevent interplane coupling and to act as a thermal spreading path. all ground pins should be connected to expand traces for low thermal resistance. the fast-switching high current ground path including the switch, catch diode and input capacitor should be kept very short. catch diode and input capacitor should be close to the chip and terminated to the same point. this path contains nanosecond rise and fall times with several amps of current. the other paths contain only dc and /or 200khz triwave and are less critical. figure 13 shows critical path layout. figure 12 indicates the high speed, high current switching path.
15 lt1510/lt1510-5 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. applicatio n s i n for m atio n wu u u d1 l1 c in gnd 1510 f11 lt1510 gnd v cc2 v cc1 prog v c bat gnd gnd gnd sw boost gnd ovp sense gnd gnd figure 13. critical electrical and thermal path layer dimensions in inches (millimeters) unless otherwise noted. package descriptio n u gn package 16-lead plastic ssop (narrow 0.150) (ltc dwg # 05-08-1641) gn16 (ssop) 0895 * 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 12 3 4 5 6 7 8 0.229 ?0.244 (5.817 ?6.198) 0.150 ?0.157** (3.810 ?3.988) 16 15 14 13 0.189 ?0.196* (4.801 ?4.978) 12 11 10 9 0.016 ?0.050 (0.406 ?1.270) 0.015 0.004 (0.38 0.10) 45 0 ?8 typ 0.0075 ?0.0098 (0.191 ?0.249) 0.053 ?0.069 (1.351 ?1.748) 0.008 ?0.012 (0.203 ?0.305) 0.004 ?0.009 (0.102 ?0.249) 0.025 (0.635) bsc n package 16-lead pdip (narrow 0.300) (ltc dwg # 05-08-1510) n16 0695 0.255 0.015* (6.477 0.381) 0.770* (19.558) max 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0.015 (0.381) min 0.125 (3.175) min 0.130 0.005 (3.302 0.127) 0.065 (1.651) typ 0.045 ?0.065 (1.143 ?1.651) 0.018 0.003 (0.457 0.076) 0.005 (0.127) min 0.100 0.010 (2.540 0.254) 0.009 ?0.015 (0.229 ?0.381) 0.300 ?0.325 (7.620 ?8.255) 0.325 +0.025 0.015 +0.635 0.381 8.255 () *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed 0.010 inch (0.254mm) s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 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) 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 0695 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc 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 * **
16 lt1510/lt1510-5 1510fc lt/gp 1197 rev c 4k ? printed in usa ? linear technology corporation 1995 linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 l (408) 432-1900 fax: (408) 434-0507 l telex: 499-3977 l www.linear-tech.com part number description comments ltc ? 1325 microprocessor-controlled battery management can charge, discharge and gas gauge nicd, nimh and pb-acid system batteries with software charging profiles lt1372/lt1377 500khz/1mhz step-up switching regulators high frequency, small inductor, high efficiency switchers, 1.5a switch lt1373 250khz step-up switching regulator high efficiency, low quiescent current, 1.5a switch lt1376 500khz step-down switching regulator high frequency, small inductor, high efficiency switcher, 1.5a switch lt1511 3a constant-voltage/constant-current battery charger high efficiency, minimal external components to fast charge lithium, nimh and nicd batteries lt1512 sepic battery charger v in can be higher or lower than battery voltage related parts typical applicatio n u dimensions in inches (millimeters) unless otherwise noted. package descriptio n u s package 16-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) 1 2 3 4 5 6 7 8 0.150 ?0.157** (3.810 ?3.988) 16 15 14 13 0.386 ?0.394* (9.804 ?10.008) 0.228 ?0.244 (5.791 ?6.197) 12 11 10 9 s16 0695 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) typ 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 * ** adjustable voltage regulator with precision adjustable current limit sw boost v cc2 1k 1k v in 18v to 25v v out 2.5v to 15v current limit level 50ma to 1a 1510 ta01 0.22 m f 0.1 m f 100 m f 30 m h lt1510 1n5819 1n914 + + pot 5k pot 100k r prog 4.93k 0.01 m f 500 m f 1 m f gnd current limit level = (2000) 2.465v r prog v cc1 prog bat ovp sense v c ()

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