View LTC1505_913256.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

1 lt1505 typical applicatio n u descriptio u features applicatio s u constant-current/voltage high efficiency battery charger figure 1. low dropout 4a lithium-ion battery charger n simple charging of li-ion, nimh and nicd batteries n very high efficiency: up to 97% n precision 0.5% charging voltage accuracy n preset battery voltages: 12.3v, 12.6v, 16.4v and 16.8v n 5% charging current accuracy n charging current programmed by resistor or dac n 0.5v dropout voltage, duty cycle > 99.5% n ac adapter current limit* maximizes charging rate n flag indicates li-ion charge completion n auto shutdown with adapter removal n only 10 m a battery drain when idle n synchronizable up to 280khz the lt ? 1505 pwm battery charger controller fast charges multiple battery chemistries including lithium-ion (li-ion), nickel-metal-hydride (nimh) and nickel-cadmium (nicd) using constant-current or constant-voltage control. maxi- mum current can be easily programmed by resistors or a dac. the constant-voltage output can be selected for 3 or 4 series li-ion cells with 0.5% accuracy. a third control loop limits the current drawn from the ac adapter during charging*. this allows simultaneous opera- tion of the equipment and fast battery charging without over- loading the ac adapter. the lt1505 can charge batteries ranging from 2.5v to 20v with dropout voltage as low as 0.5v. synchronous n-channel fets switching at 200khz give high efficiency and allow small inductor size. a diode is not required in series with the battery because the charger automatically enters a 10 m a sleep mode when the wall adapter is un- plugged. a logic output indicates li-ion full charge when current drops to 20% of the programmed value. the lt1505 is available in a 28-pin ssop package. n notebook computers n portable instruments n chargers for li-ion, nimh, nicd and lead acid rechargeable batteries , ltc and lt are registered trademarks of linear technology corporation. 5 w c prog 1 m f 300 c7 0.68 m f c6 0.1 m f c3 2.2 m f c out 22 m f 25v 2 c2 0.68 m f v bat 12.6v battery note: dbody is the body diode of m3 c in : sanyo os-con l1: sumida cdrh127-150 (can be from 10 h to 30 h) m1 si4412 m2 si4412 d4 mbrs140 d2 mmsd4148t1 d3 mmsd4148t1 r7 500 w 100k r5 4k r1 1k r6 4k *body diode polarity must be as shown r s4 0.025 w m3 si4435 dbody* to system power v in (from adapter) r s1 0.025 w l1 15 m h 1505 f01 r prog 4.93k 1% 0.33 m f r x4 3k r s2 200 w 1% r s3 200 w 1% c in 47 m f 35v c1 1 m f c4 0.1 m f bat2 bat sense lt1505 v cc boost boostc spin pgnd agnd 4.1v 4.2v v fb 3 cell prog v c bgate comp1 cap flag shdn sync uv infet sw tgate gbias clp cln *us patent no. 5,723,970
2 lt1505 v cc , clp, cln, infet, uv, 3cell, flag ................ 27v sw voltage with respect to gnd ........................... C 2v boost, boostc voltage with respect to v cc ....... 10v gbias ..................................................................... 10v sync, bat2, bat, sense, spin ............................ 20v v c , prog, v fb , 4.1v, 4.2v ........................................ 7v cap, shdn .......................................................... 3ma absolute m axi m u m ratings w ww u (note 1) tgate, bgate current continuous ....................... 0.2a tgate, bgate output energy (per cycle) ............... 2 m j maximum operating v cc ......................................... 24v operating ambient temperature range ....... 0 c to 70 c operating junction temperature range .... 0 c to 125 c storage temperature range ................. C 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c order part number lt1505cg lt1505cg-1 order part number t jmax = 125 c, q ja = 100 c/ w consult factory for industrial and military grade parts. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 top view g package 28-lead plastic ssop 28 27 26 25 24 23 22 21 20 19 18 17 16 15 boost tgate sw sync shdn agnd uv infet clp cln comp1 cap flag 4.1v pgnd bgate gbias boostc v cc bat spin sense bat2 prog v c v fb 3cell 4.2v t jmax = 125 c, q ja = 100 c/ w 1 2 3 4 5 6 7 8 9 10 11 12 13 14 top view g package 28-lead plastic ssop 28 27 26 25 24 23 22 21 20 19 18 17 16 15 boost tgate sw sync shdn agnd uv infet nc nc gnd cap flag 4.1v pgnd bgate gbias boostc v cc bat spin sense bat2 prog v c v fb 3cell 4.2v note: lt1505cg-1 does not have input current limiting function. electrical characteristics package/order i n for m atio n w u u the l denotes specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v cc = 18v, v bat = 12.6v, v cln = v cc (lt1505), no load on any outputs unless otherwise noted. parameter conditions min typ max units overall supply current v cc 24v l 12 15 ma sense amplifier ca1 gain and input offset voltage 11v v cc 24v , 0v v bat 20v (with r s2 = 200 w , r s3 = 200 w )r prog = 4.93k 95 100 105 mv (measured across r s1 , figure 1) (note 2) r prog = 4.93k l 92 108 mv r prog = 49.3k 7 10 13 mv boost pin current v boost = v sw + 8v, 0v v sw 20v tgate high 2 3 ma tgate low 2 3 ma boostc pin current v boostc = v cc + 8v 1 ma reference reference voltage (note 3) r prog = 4.93k, measured at v fb with v a 2.453 2.465 2.477 v supplying i prog and switching off reference voltage tolerance 11v v cc 24v l 2.441 2.489 v
3 lt1505 parameter conditions min typ max units preset battery voltage (12.3v, 16.4v, 12.6v, 16.8v) all preset battery voltages measured at bat2 pin 0.5 % preset battery voltage tolerance (v bat + 0.3v) v cc 24v l C1 1 % bat2 pin input current v bat2 = v preset C 1v l 6 m a voltage setting resistors tolerance (r4, r5, r6, r7) C 40 40 % shutdown undervoltage lockout (tgate and bgate off) measured at uv pin l 6.3 6.7 7.25 v threshold (note 9) uv pin input current 0v v uv 8v l C1 5 m a reverse current from battery in micropower v bat 20v, v uv 0.4v, 10 30 m a shutdown (note 10) v cc = v sw = battery voltage shutdown threshold at shdn pin when v cc l 12v is connected shdn pin current 0v v shdn 3v 8 m a supply current in shutdown v cc 24v 15 20 ma (v shdn is low, v cc is connected) minimum i prog for switching on C 1 C 4 C 22 m a minimum i prog for switching off at v prog 1v l C1 C2.4 ma current sense amplifier ca1 inputs (sense, bat) input bias current (sense, bat) v shdn = high l C 50 C 120 m a v shdn = low (shutdown) C 10 m a input common mode low l C 0.25 v input common mode high l v cc C 0.3 v spin input current v shdn = high, v spin 3 2v (note 8) l 2ma v shdn = low (shutdown) 10 m a oscillator switching frequency (f nom ) 180 200 220 khz switching frequency tolerance l 170 200 230 khz sync pin input current v sync = 0v C 0.5 ma v sync = 2v C 30 m a synchronization pulse threshold on sync pin 0.9 1.2 2.0 v synchronization frequency l 240 280 khz maximum duty cycle v boost threshold to turn tgate off measured at (v boost C v sw ) (comparator a2) (note 4) low to high l 6.8 7.3 7.6 v hysteresis 0.25 v maximum duty cycle of natural frequency 200khz l 85 90 % (note 5) current amplifier ca2 transconductance v c = 1v, i vc = 1 m a 150 200 300 m mho maximum v c for switch off l 0.6 v i vc current (out of pin) v c 3 0.6v l 50 m a v c < 0.45v l 3ma v c at shutdown v shdn = low (shutdown) l 0.35 v electrical characteristics the l denotes specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v cc = 18v, v bat = 12.6v, v cln = v cc (lt1505), no load on any outputs unless otherwise noted.
4 lt1505 note 6: see lithium-ion charging completion in the applications information section. note 7: tested with test circuit 3. note 8: i spin keeps switching on to keep v bat regulated when battery is not present to avoid high surge current from c out when battery is inserted. note 9: above undervoltage threshold switching is enabled. note 10: do not connect v cc directly to v in (see figure 1). this connection will cause the internal diode between v bat and v cc to be forward-biased and may cause high current to flow from v in . when the adapter is removed, v cc will be held up by the body diode of m1. note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: tested with test circuit 1. note 3: tested with test circuit 2. note 4: when v cc and battery voltage differential is low, high duty factor is required. the lt1505 achieves a duty factor greater than 99% by skipping cycles. only when v boost drops below the comparator a2 threshold will tgate be turned off. see applications information. note 5: when the system starts, c2 (boost cap) has to be charged up to drive tgate and to start the system. the lt1505 will keep tgate off and turn bgate on for 0.2 m s at 200khz to charge up c2. comparator a2 senses v boost and switches to the normal pwm mode when v boost is above the threshold. electrical characteristics the l denotes specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. v cc = 18v, v bat = 12.6v, v cln = v cc (lt1505), no load on any outputs unless otherwise noted. parameter conditions min typ max units voltage amplifier va transconductance (note 3) output current from 50 m a to 500 m a 0.21 0.6 1.0 mho output source current v fb = v prog = v ref + 10mv 1.1 ma v fb input bias current at 0.5ma va output current, t a < 70 c C 10 25 na (3 cell, 4.1v, 4.2v are not connected, v bat2 = 0v) current limit amplifier cl1 turn-on threshold 0.5ma output current 87 92 97 mv transconductance output current from 50 m a to 500 m a 0.5 1 3 mho clp input current 0.5ma output current 1 3 m a cln input current 0.5ma output current 0.8 2 ma input p-channel fet driver (infet) infet on clamping voltage (v cc C v infet )v cc 3 11v l 6.5 7.8 9 v infet on driver current v infet = v cc C 6v l 820 ma infet off clamping voltage (v cc C v infet )v cc not connected, i infet < C 2 m a 1.4 v infet off drive current v cc not connected, (v cc C v infet ) 3 2v C 2.5 ma charging completion flag (comparator e6) charging completion threshold (note 6) measured at v rs1 , v cap = 2v (note 7) 14 20 28 mv threshold on cap pin low to high threshold l 3.3 4.2 v high to low threshold l 0.6 v v cap at shutdown v shdn = low (shutdown) l 0.13 0.3 v flag (open collector) output low v cap = 4v, i flag < 1ma l 0.3 v flag pin leakage current v cap = 0.6v l 3 m a gate drivers (tgate, bgate) v gbias 11v < v cc < 24v, i gbias 15ma l 8.4 9.1 9.6 v v shdn = low (shutdown) l 13 v v tgate high (v tgate C v sw )i tgate 20ma, v boost = v gbias C 0.5v l 5.6 6.6 v v bgate high i bgate 20ma l 6.2 7.2 v v tgate low (v tgate C v sw )i tgate 50ma l 0.8 v v bgate low i bgate 50ma l 0.8 v peak gate drive current 10nf load 1 a gate drive rise and fall time 1nf load 25 ns v tgate , v bgate at shutdown v shdn = low (shutdown) l 1v i tgate = i bgate = 10 m a
5 lt1505 typical perfor m a n ce characteristics uw i bat (a) 0 efficiency (%) 105 100 95 90 85 80 4 1505 g01 1 2 3 5 v in = 19v v bat = 12.6v efficiency of figure 1 circuit i va (ma) 0 ? v fb (mv) 4 3 2 1 0 0.8 1505 g04 0.2 0.1 0.3 0.5 0.7 0.9 0.4 0.6 1.0 125 c 25 c v cc (v) 15 14 13 12 11 10 i cc (ma) 1505 g06 10 13 16 19 22 25 0 c 25 c 125 c i gbias (ma) 9.2 9.1 9.0 8.9 8.8 8.7 8.6 8.5 8.4 8.3 8.1 v gbias (v) 1505 g02 0 246 ? ?0 ?2 14 ?6 18 ?0 0 c 25 c 125 c v gbias vs i gbias d v fb vs i va (voltage amplifier) temperature ( c) 0 255075100 threshold (mv) 125 1505 g05 98 96 94 92 90 88 current limit amplifier cl1 threshold i cc vs v cc junction temperature ( c) 0 reference voltage (v) 2.470 2.468 2.466 2.464 2.462 2.460 2.458 25 50 75 100 1505 g09 125 150 reference voltage vs temperature v prog (v) 0123 5 4 i prog (ma) 6 0 ? 1505 g07 125 c current feedback amplifier open loop 25 c prog pin characteristics v c (v) 1.2 1.0 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1.0 i vc (ma) 1505 g08 0 0.4 0.6 0.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0 v c pin characteristics v ref line regulation v cc (v) 0 ? v ref (v) 0.003 0.002 0.001 0 0.001 0.002 0.003 5 10 15 20 1505 g03 25 30 all temperatures 0 c t j 125 c
6 lt1505 pi n fu n ctio n s uuu boost (pin 1): this pin is used to bootstrap and supply power for the topside power switch gate drive and control circuity. in normal operation, v boost is powered from an internally generated 8.6v regulator v gbias , v boost ? v cc + 9.1v when tgate is high. do not force an external voltage on boost pin. tgate (pin 2): this pin provides gate drive to the topside power fet. when tgate is driven on, the gate voltage will be approximately equal to v sw + 6.6v. a series resistor of 5 w to 10 w should be used from this pin to the gate of the topside fet. sw (pin 3): this pin is the reference point for the floating topside gate drive circuitry. it is the common connection for the top and bottom side switches and the output inductor. this pin switches between ground and v cc with very high dv/dt rates. care needs to be taken in the pc layout to keep this node from coupling to other sensitive nodes. a 1a schottky clamp diode should be placed from this pin to the ground pin, using very short traces to prevent the chip substrate diode from turning on. see applications information for more details. sync (pin 4): synchronization input. the lt1505 can be synchronized to an external clock with pulses that have duty cycles between 10% and 95%. an internal one shot that is triggered on the rising edge of the sync pulse makes this input insensitive to the duty cycle of the sync pulse. the input voltage range on this pin is 0v to 20v. this pin can float if not used. shdn (pin 5): shutdown. when this pin is pulled below 1v, switching will stop, gbias will go low and the input cur- rents of ca1 will be off. note that input current of about 4 m a keeps the device in shutdown unless an external pull-up signal is applied. the voltage range on this pin is 0v to v cc . agnd (pin 6): low current analog ground. uv (pin 7): undervoltage lockout input. the rising thresh- old is 6.7v with a hysteresis of 0.5v. switching stops in undervoltage lockout. when the input supply (normally the wall adapter output) to the chip is removed, the uv pin must be pulled down to below 0.7v (a 5k resistor from adapter output to gnd is required), otherwise the reverse- battery current will be approximately 200 m a instead of 10 m a. do not leave the uv pin floating. if it is connected to v in with no resistor divider, the built-in 6.7v undervoltage lockout will be effective. maximum voltage allowed on this pin is v cc . infet (pin 8): for very low dropout applications, an external p-channel mosfet can be used to connect the input supply to v cc . this pin provides the gate drive for the pfet. the gate drive is clamped to 8v below v cc . the gate is driven on (low) when v cc >(v bat + 0.2v) and v uv > 6.7v. the gate is off (high) when v cc < (v bat + 0.2v). the body diode of the pfet is used to pull up v cc to turn on the lt1505. clp (pin 9): lt1505: positive input to the input current limit amplifier cl1. the threshold is set at 92mv. when used to limit input current, a filter is needed to filter out the 200khz switching noise. (lt1505-1: no connection.) cln (pin 10): lt1505: negative input to the input current limit amplifier cl1. when used, both clp and cln should be connected to a voltage higher than 6v and normally v cc (to the v cc bypass capacitor for less noise). maximum voltage allowed on both clp and cln is v cc + 1v. (lt1505-1: no connection.) comp1 (pin 11): lt1505: compensation node for the input current limit amplifier cl1. at input adapter current limit, this pin rises to 1v. by forcing comp1 low with an external transistor, amplifier cl1 will be disabled (no adapter current limit). output current is less than 0.2ma. see the figure 1 circuit for the required resistor and capacitor values. (lt1505-1: connect to gnd.) cap (pin 12): a 0.1 m f capacitor from cap to ground is needed to filter the sampled charging current signal. this filtered signal is used to set the flag pin when the charging current drops below 20% of the programmed maximum charging current. flag (pin 13): this pin is an open-collector output that is used to indicate the end of charge. the flag pin is driven low when the charge current drops below 20% of the programmed charge current. a pull-up resistor is required if this function is used. this pin is capable of sinking at least 1ma. maximum voltage on this pin is v cc . 4.1v (pin 14), 4.2v (pin 15), 3cell (pin 16), v fb (pin 17): these four pins are used to select the battery voltage using the preset internal resistor network. the v fb pin is
7 lt1505 the noninverting input to the amplifier, va in the block diagram, that controls the charging current when the device operates in constant voltage mode. the amplifier va controls the charging current to maintain the voltage on the v fb pin at the reference voltage (2.465v). input bias current for va is approximately 3na. the lt1505 incorpo- rates a resistor divider that can be used to select the correct voltage for either three or four 4.1v or 4.2v lithium-ion cells. for three cells the 3cell pin is shorted to the v fb pin. for four cells the 3cell pin is not con- nected. for 4.1v cells the 4.1v pin is connected to the v fb pin and the 4.2v pin is not connected. for 4.2v cells the 4.2v pin is connected to v fb and the 4.1v pin is not connected. see the table below. preset battery voltage pin selection 12.3v (3 4.1v cell) 4.1v, v fb , 3cell short together 16.4v (4 4.1v cell) 4.1v, v fb , short together, 3cell floats 12.6v (3 4.2v cell) 4.2v, v fb , 3cell short together 16.8v (4 4.2v cell) 4.2v, v fb , short together, 3cell floats for battery voltages other than the preset values, an external resistor divider can be used. if an external divider is used then the 4.1v, 4.2v and 3cell pins should not be connected and bat2 pin should be grounded. to maintain the tight voltage tolerance, the external resistors should have better than 0.25% tolerance. note that the v fb pin will float high and inhibit switching if it is left open. v c (pin 18): this is the control signal of the inner loop of the current mode pwm. switching starts at 0.9v, higher v c corresponds to higher charging current in normal operation and reaches 1.1v at full charging current. a capacitor of at least 0.33 m f to gnd filters out noise and controls the rate of soft start. pulling this pin low will stop switching. typical output current is 60 m a. prog (pin 19): this pin is for programming the charge current and for system loop compensation. during normal operation, v prog stays at 2.465v. if it is shorted to gnd or more than 1ma is drawn out of the pin, switching will stop. when a microprocessor controlled dac is used to pro- gram charging current, it must be capable of sinking current at a compliance up to 2.465v. pi n fu n ctio n s uuu bat2 (pin 20): this pin is used to connect the battery to the internal preset voltage setting resistor. an internal switch disconnects the internal divider from the battery when the device is in shutdown or when power is discon- nected. this disconnect function eliminates the current drain due to the resistor divider. this pin should be connected to the positive node of the battery if the internal preset divider is used. this pin should be grounded if an external divider is used. maximum input voltage on this pin is 20v. sense (pin 21): this pin is the noninverting input to the current amplifier ca1 in the block diagram. typical bias current is C 50 m a. spin (pin 22): this pin is for the internal amplifier ca1 bias. it must be connected as shown in the application circuit. bat (pin 23): current amplifier ca1 inverting input. typical bias current is C 50 m a. v cc (pin 24): input supply. for good bypass, a low esr capacitor of 10 m f or higher is required. keep the lead length to a minimum. v cc should be between 11v and 24v. do not force v cc below v bat by more than 1v with the battery present. boostc (pin 25): this pin is used to bootstrap and supply the current sense amplifier ca1 for very low dropout condition. v cc can be as low as only 0.4v above the battery voltage. a diode and a capacitor are needed to get the voltage from v boost . if low dropout is not needed and v cc is always 3v or higher than v bat , this pin can be left floating or tied to v cc . do not force this pin to a voltage lower than v cc . typical input current is 1ma. gbias (pin 26): this is the output of the internal 9.1v regulator to power the drivers and control circuits. this pin must be bypassed to a ground plane with a minimum of 2.2 m f ceramic capacitor. switching will stop when v gbias drops below 7v. bgate (pin 27): low side power mosfet drive. pgnd (pin 28): mosfet driver power ground. a solid system ground plane is very important. see the lt1505 demo manual for further information.
8 lt1505 block diagra m w + + a2 a3 7v a1 2 50k c3 4.7 m f l1 10 m h r s1 vr s1 + tgate v cc 3 sw 1 boost m1 m2 + 2.5v bgate + 9.1v 12.6v battery + + + a4 a6 4v sw + + + a12 0.02v pwm slope comp q2 q1 ca1 + + + a11 i prog vr s1 + + e4 1.3v 4u + 50k a5 a9 a7 a8 26 gbias 27 bgate 28 pgnd 22 spin r s3 21 sense 23 bat 20 bat2 16 3cell 17 v fb 14 4.1v r4 50.55k r5 21k 15 4.2v r6 0.33k r7 12.3k r prog c prog v ref 2.465v v in v cc r1 1k r2 r3 r8 75k 25 boostc c2 1 m f sr shutdown a10 i va v ref i prog b1 + e6 + ca2 c1 r s2 i bat + + cl1* *lt1505 only. see pin functions for lt1505-1 connections comp1 1505 bd prog v c 9 clp 92mv 10 11 19 18 cln system load agnd 6 q3 va osc 200k one shot sync 4 flag 13 5 shdn + e5 7v + gbias bat 3.3v i prog + + e1 shutdown v cc v in 24 uv v cc 7 8 + e2 6.7v + + + e8 6.7v 0.2v + e3 a13 q4 7.8v v cc infet v cc v in cap 12 e7 + r s i va 4 (lt1505)
9 lt1505 test circuits + + ca1 + + ? va v ref i va r s3 200 w 10k 10k 4.93k i prog i prog sense bat prog lt1505 1505 tc03 0.047 m f 0.47 m f 0.033 m f 3.3v 2.465v lt1013 flag + v bat v rs1 + + + 2v 1k + v fb cap 20k r s2 200 w 10 w e6 lt1013 i va 4 test circuit 1 test circuit 3 test circuit 2 v ref 2.465v + + va + 2k 2nf v fb or bat2 1505 tc02 i prog r prog lt1505 prog lt1013 0.47 m f + v ref ? 0.65v v bat v c ca2 + + ca1 + 300 w 20k 1k 1k r s1 10 bat sense spin 1505 tc01 prog r prog 0.047 m f lt1505 1 m f 75k lt1006 + r s2 200 r s3 200
10 lt1505 the lt1505 is a synchronous current mode pwm step- down (buck) switcher. the battery dc charge current is pro- grammed by a resistor r prog (or a dac output current) at the prog pin and the ratio of sense resistors r s2 over r s1 (see block diagram). amplifier ca1 converts the charge cur- rent through r s1 to a much lower current i prog (i prog = i bat ? rs1/rs2) fed into the prog pin. amplifier ca2 com- pares 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 supplies the topside power switch gate drive. the lt1505 generates an 9.1v v gbias to power drives and v boostc . boostc pin supplies the current amplifier ca1 with a voltage higher than v cc for low dropout appli- cation. for batteries like lithium that require both constant- current and constant-voltage charging, the 0.5% 2.465v reference and the amplifier va reduce the charge current when battery voltage reaches the preset level. for nimh and nicd, va can be used for overvoltage protection. the amplifier cl1 monitors and limits the input current, normally from the ac adapter, to a preset level (92mv/r s ). at input current limit, cl1 will supply the programming current i prog , thus reducing battery charging current. to prevent current shoot-through between topside and lowside switches, comparators a3 and a4 assure that one switch turns off before the other is allowed to turn on. comparator a12 monitors charge current level and turns lowside switch off if it drops below 20% of the programmed value (20mv across r s1 ) to allow for inductor discontinu- ous mode operation. therefore sometimes even in con- tinuous mode operation with light current level the lowside switch stays off. comparator e6 monitors the charge current and signals through the flag pin when the charger is in voltage mode and the charge current level is reduced to 20%. this charge complete signal can be used to start a timer for charge termination. the infet pin drives an external p-channel fet for low dropout application. when input voltage is removed, v cc will be held up by the body diode of the topside mosfet. the lt1505 goes into a low current, 10 m a typical, sleep mode as v cc drops below the battery voltage. to shut down the charger simply pull the v c pin or shdn pin low with a transistor. operatio n u applicatio n s i n for m atio n wu u u input and output capacitors in the 4a lithium battery charger (figure 1), 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 capaci- tors 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 the manufac- turer before use. alternatives include new high capacity ceramic (at least 20 m f) from tokin or united chemi-con/ marcon, et al. the output capacitor (c out ) is also assumed to absorb output switching current ripple. the general formula for capacitor current is: i rms = (l1)(f) v bat v cc () 0.29 (v bat ) 1 for example, v cc = 19v, v bat = 12.6v, l1 = 15 m h, and f = 200khz, i rms = 0.4a.
11 lt1505 applicatio n s i n for m atio n wu u u emi considerations usually make it desirable to minimize ripple current in the battery leads. 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 imped- ance. if the esr of c out is 0.2 w and the battery impedance is raised to 4 w with a bead or inductor, only 5% of the ripple current will flow in the battery. soft start and undervoltage lockout the lt1505 is soft started by the 0.33 m f capacitor on the v c pin. on start-up, the v c pin voltage will rise quickly to 0.5v, then ramp up at a rate set by the internal 45 m a pull- up current and the external capacitor. battery charge current starts ramping up when v c voltage reaches 0.7v and full current is achieved with v c at 1.1v. with a 0.33 m f capacitor, time to reach full charge current is about 10ms and it is assumed that input voltage to the charger will reach full value in less than 10ms. the capacitor can be increased up to 1 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 30w, a 15v adapter might be current limited at 2.5a. if adapter voltage is less than (30w/2.5a = 12v) when full power is drawn, the adapter voltage will be pulled down by the constant 30w load until it reaches a lower stable state where the switching regu- lators can no longer supply full load. this situation can be prevented by setting undervoltage lockout higher than the minimum adapter voltage where full power can be achieved. figure 2. adapter current limiting 92mv + 500 clp cln v cc uv 1505 f02 r5 lt1505 r6 1 m f + r s4 * c in v in cl1 ac adapter output *r s4 = 92mv adapter current limit + a resistor divider is used to set the desired v cc lockout voltage as shown in figure 2. a typical value for r6 is 5k and r5 is found from: r5 = r6(v v ) v uv uv in v uv = rising lockout threshold on the uv pin v in = charger input voltage that will sustain full load power example: with r6 = 5k, v uv = 6.7v and setting v in at 16v; r5 = 5k (16v C 6.7v)/6.7v = 6.9k the resistor divider should be connected directly to the adapter output as shown, not to the v cc pin to prevent battery drain with no adapter voltage. if the uv pin is not used, connect it to the adapter output (not v cc ) and connect a resistor no greater than 5k to ground. floating the pin will cause reverse battery current to increase from 10 m a to 200 m a. adapter current limiting (not applicable for the lt1505-1) an important feature of the lt1505 is the ability to automatically adjust charge current to a level which avoids overloading the wall adapter. this allows the product to operate at the same time batteries are being charged without complex load management algo rithms. addition- ally, batteries will automatically be charged at the maximum possible rate of which the adapter is capable.
12 lt1505 applicatio n s i n for m atio n wu u u this is accomplished by sensing total adapter output current and adjusting charge current downward if a preset adapter current limit is exceeded. true analog control is used, with closed loop feedback ensuring that adapter load current remains within limits. amplifier cl1 in figure 2 senses the voltage across r s4 , connected between the clp and cln pins. when this voltage exceeds 92mv, the amplifier will override programmed charge current to limit adapter current to 92mv/r s4 . a lowpass filter formed by 500 w and 1 m f is required to eliminate switching noise. if the current limit is not used, then the r7 /c1 filter and the comp1 (r1/c7) compensation networks are not needed, and both clp and cln pins should be connected to v cc . charge current programming the basic formula for charge current is (see block diagram): i bat = i prog = 2.465v r prog r s2 r s1 ()() r s2 r s1 () where r prog is the total resistance from prog pin to ground. for the sense amplifier ca1 biasing purpose, r s3 should have the same value as r s2 and spin should be connected directly to the sense resistor (r s1 ) as shown in the block diagram. for example, 4a charging current is needed. for low power dissipation on r s1 and enough signal to drive the amplifier ca1, let r s1 = 100mv/4a = 0.025 w . this limits r s1 power to 0.4w. let r prog = 5k, then: r s2 = r s3 = = = 200 (i bat )(r prog )(r s1 ) 2.465v (4a)(5k)(0.025) 2.465v charge 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 3). charge 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 charge current, it must be capable of sinking current at a compliance up to 2.5v if connected directly to the prog pin. lithium-ion charging the 4a lithium battery charger (figure 1) charges lithium- ion batteries at a constant 4a until battery voltage reaches the preset value. the charger will then automatically go into a constant-voltage mode with current decreasing to near zero over time as the battery reaches full charge. preset battery voltage settings the lt1505 provides four preset battery voltages: 12.3v, 12.6v, 16.4v and 16.8v. see the pin functions section for pin setting voltage selection. an internal switch connects the resistor dividers to the battery sense pin, bat2. when shutting down the lt1505 by removing adaptor power or by pulling the shdn pin low, the resistor dividers will be disconnected and will not drain the battery. the bat2 pin should be connected to the battery when any of the preset battery voltages are used. external battery voltage setting resistors when an external divider is used for other battery voltages, bat2 should be grounded. pins 4.1v, 4.2v and 3cell should be left floating. to minimize battery drain when the charger is off, current through the r3/r4 divider (figure 4) is set at 15 m a . the input current to the v fb pin is 3na and the error can be neglected. pwm r prog 4.7k prog c prog 1 m f q1 vn2222 5v 0v lt1505 1505 f03 i bat = (dc)(4a) figure 3. pwm current programming
13 lt1505 with divider current set at 15 m a, r4 = 2.465/15 m a = 162k and, r3 r4 v 2.465 2.465 162k 8.4 2.465 2.465 390k bat = () - () = - () = li-ion batteries typically require float voltage accuracy of 1% to 2%. accuracy of the lt1505 v fb voltage is 0.5% at 25 c and 1% over the full temperature range. this leads to the possibility that very accurate (0.1%) resistors might be needed for r3 and r4. actually, the temperature of the lt1505 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. applicatio n s i n for m atio n wu u u v bat 1505 f04 8.4v r3 390k 0.25% r4 162k 0.25% + v fb lt1505 figure 4. external resistor divider lithium-ion charging completion some battery manufacturers recommend termination of constant-voltage float mode after charge current has dropped below a specified level (typically around 20% of the full current) and a further time-out period of 30 minutes to 90 minutes has elapsed. check with manufac- turers for details. the lt1505 provides a signal at the flag pin when charging is in voltage mode and current is reduced to 20% of full current, assuming full charge current is programmed to have 100mv across the current sense resistor (v rs1 ). the comparator e6 in the block diagram compares the charge current sample i prog to the output current i va voltage amplifier va. when the charge current drops to 20% of full current, i prog will be equal to 0.25 i va and the open-collector output v flag will go low and can be used to start an external timer. when this feature is used, a capacitor of at least 0.1 m f is required at the cap pin to filter out the switching noise and a pull-up resistor is also needed at the flag pin. if this feature is not used, c6 is not needed. very low dropout operation the lt1505 can charge the battery even when v cc goes as low as 0.5v above the combined voltages of the battery and the drops on the sense resistor as well as parasitic wiring. this low v cc sometimes requires a duty factor greater then 99% and tgate stays on for many switching cycles. while tgate stays on, the voltage v boost across the capacitor c2 drops down because tgate control circuits require 2ma dc current. c2 needs to be recharged before v boost drops too low to keep the topside switch on. a unique design allows the lt1505 to operate under these conditions; the comparator a2 moni- tors v boost and when it drops from 9.1v to 6.9v, tgate will be turned off for about 0.2 m s to recharge c2. note that the lt1505 gets started the same way when power turns on and there is no initial v boost . it is important to use 0.56 m f or greater value for c2 to hold v boost up for a sufficient amount of time. when minimum operating v cc is less than 2.5v above the battery voltage, d3 and c4 (see figure 1) are also needed to bootstrap v boostc higher than v cc to bias the current amplifier ca1. they are not needed if v cc is at least 2.5v higher than v bat . the pfet m3 is optional and can be replaced with a diode if v in is at least 3v higher than v bat . the gate control pin infet turns on m3 when v in gets up above the undervoltage lockout level set by r5 and r6 and is clamped internally to 8v below v cc . in sleep mode when v in is removed, infet will clamp m3 v sg to 0.2v. shutdown when adapter power is removed, v cc will drift down and be held by the body diode of the topside nfet switch. as soon as v cc goes down to 0.2v above v bat , the lt1505 will go into sleep mode drawing only 10 m a from the battery. there are two ways to stop switching: pulling the shdn pin low or pulling the v c pin low. pulling the shdn pin low will also turn off v gbias and ca1 input currents. pulling the v c pin low will only stop switching and v gbias stays high. make sure there is a pull-up resistor on the shdn pin even
14 lt1505 if the shdn pin is not used, otherwise internal pull-down current will keep the shdn pin low and switching off when power turns on. each tgate and bgate pin has a 50k pull-down resistor to keep the external power fets off when shut down or power is off. note that maximum operating v cc is 24v. for short transients the lt1505 can be operated as high as 27v. for v cc higher than 24v it is preferred to use the v c pin to shut down. if the shdn pin has to be used to shut down at v cc higher than 24v, the figure 5 pull-up circuit must be used to slow down the v gbias ramp-up rate when the shdn pin is released. otherwise, high surge current charging the bypass capacitor might damage the lt1505. for v cc less than 24v, only a 100k resistor and no capacitor is needed at shdn pin to v in for pull-up. synchronization the lt1505 can be synchronized to a frequency range from 240khz to 280khz. with a 200ns one-shot timer on chip, the lt1505 provides flexibility on the synchronizing pulse width. sync pulse threshold is about 1.2v (figure 6). nickel-cadmium and nickel-metal-hydride charging the circuit in the 4a lithium battery charger (figure 1) can be modified to charge nicd or nimh batteries. for example, 2-level charging is needed; 2a when q1 is on, and 200ma when q1 is off (figure 7). for 2a full current, the current sense resistor (r s1 ) should be increased to 0.05 w so that enough signal (10mv) will be across r s1 at 0.2a trickle charge to keep charging current accurate. for a 2-level charger, r1 and r2 are found from: r1 2.465 4000 i r2 2.465 4000 ii low hi low = ()() = ()() - all battery chargers with fast charge rates require some means to detect full charge state in the battery to terminate the high charge current. nicd batteries are typically charged at high current until temperature rise or battery voltage decrease is detected as an indication of near full charge. applicatio n s i n for m atio n wu u u figure 5. high input voltage shudown figure 6. synchronizing with external clock r2 5.49k r1 49.3k prog c prog 1 f q1 lt1505 1505 f07 5v to 20v vn2222 pulse width > 200ns 5k sync 1505 f06 lt1505 the charge current is then reduced to a much lower value and maintained as a constant trickle charge. an interme- diate 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 C d v as an indicator of full charge, and an increase in temperature is more often used with a temperature sensor in the battery pack. secondly, constant trickle charge may not be recommended. figure 7. 2-level charging shdn 1505 f05 3m v in 24v v cc < 27v open drain 3.3 m f lt1505
15 lt1505 applicatio n s i n for m atio n wu u u for at least 1a is necessary to clamp the sw pin and should be placed close to the low side mosfet. a ground plane should be used under the switching circuitry to prevent interplane coupling and to act as a thermal spreading path. note that the inductor is probably the most heat dissipat- ing device in the charging system. the resistance on a 4a, 15 m h inductor, can be 0.03 w . with dc and ac losses, the power dissipation can go as high as 0.8w. expanded traces should be used for the inductor leads for low thermal resistance. the fast switching high current ground path including the mosfets, d4 and input bypass capacitor should be kept very short. another smaller input bypass (1 m f ceramic) should be placed very close the chip. the demo board dc219 should be used for layout reference. figure 9. v bat crowbar protection 1505 f09 shdn lt1505 d5 1n4148 100k v bat v in m3 1505 f08 m4 tpo610 r s4 infet lt1505 v cc v in figure 8. v in crowbar protection 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. please contact the linear technology applications department about charge termination circuits. if overvoltage protection is needed, r3 and r4 in figure 4 should be calculated according to the procedure described in the lithium-ion charging section. the v fb pin should be grounded if not used. charger crowbar protection if the v in connector of figure 1 can be instantaneously shorted (crowbarred) to ground, then a small p-channel fet m4 should be used to quickly turn off the input p-channel fet m3 (see figure 8), otherwise, high reverse surge current might damage m3. m3 can also be replaced by a diode if dropout voltage and heat dissipation are not problems. note that the lt1505 will operate even when v bat is grounded. if v bat of figure 1 charger gets shorted to ground very quickly (crowbarred) from a high battery voltage, slow loop response may allow charge current to build up and damage the topside n-channel fet m1. a small diode d5 (see figure 9) from the shdn pin to v bat will shut down switching and protect the charger. note that m4 and/or d5 are needed only if the charger system can be potentially crowbarred. layout considerations switch rise and fall times are under 20ns for maximum efficiency. to prevent radiation, the power mosfets, the sw pin and input bypass capacitor leads should be kept as short as possible. a schottky diode (d4 in figure 1) rated 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.
16 lt1505 1505fb lt/tp 0900 2k rev b ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com dimensions in inches (millimeters) unless otherwise noted. package descriptio n u g package 28-lead plastic ssop (0.209) (ltc dwg # 05-08-1640) g28 ssop 0694 0.005 ?0.009 (0.13 ?0.22) 0 ?8 0.022 ?0.037 (0.55 ?0.95) 0.205 ?0.212** (5.20 ?5.38) 0.301 ?0.311 (7.65 ?7.90) 1234 5 6 7 8 9 10 11 12 14 13 0.397 ?0.407* (10.07 ?10.33) 25 26 22 21 20 19 18 17 16 15 23 24 27 28 0.068 ?0.078 (1.73 ?1.99) 0.002 ?0.008 (0.05 ?0.21) 0.0256 (0.65) bsc 0.010 ?0.015 (0.25 ?0.38) dimensions do not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimensions do not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * ** part number description comments ltc ? 1325 microprocessor-controlled battery management system can charge, discharge and gas gauge nicd and lead-acid batteries with software charging profiles lt1372/lt1377 1.5a, 500khz/1mhz step-up switching regulators high frequency, small inductor, high efficiency switchers, so-8 lt1376 1.5a, 500khz step-down switching regulator high frequency, small inductor, high efficiency switcher, so-8 lt1510 constant-voltage/constant-current battery charger up to 1.5a charge current, small so-8 footprint lt1511 3a constant-voltage/constant-current battery charger charges lithium, nicd and nimh batteries, 28-lead so package lt1512 sepic cc/cv battery charger v in can be higher or lower than battery voltage, 2a internal switch lt1513 sepic cc/cv battery charger v in can be higher or lower than battery voltage, 3a internal switch ltc1731 linear charger programmable timer; 8-pin msop; c/10 flag ltc1732 linear charger ac adapter present flag; programmable timer; 10-pin msop; c/10 flag ltc1759 smbus controlled smart battery charger lt1505 charger functionality with smbus control lt1769 2a constant-voltage/constant-current battery charger charges lithium, nicd and nimh batteries, 28-lead ssop related parts ? linear technology corporation 1999

▲Up To Search▲

Price & Availability of LTC1505

	To Download LTC1505 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .