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ltc4001-1 1 40011fa typical application features applications description 2a synchronous buck li-ion charger the ltc ? 4001-1 is a 2a li-ion battery charger intended for 5v wall adapters. it utilizes a 1.5mhz synchronous buck converter topology to reduce power dissipation during charging. low power dissipation, an internal mosfet and sense resistor allow a physically small charger that can be embedded in a wide range of handheld applications. the ltc4001-1 includes complete charge termination circuitry, automatic recharge and a 1% 4.1v ? oat voltage. input short-circuit protection is included so no blocking diode is required. this 4.1v version of the standard ltc4001 is intended for applications which will be operated or stored above approximately 60c. under these conditions, the reduced ? oat voltage will trade-off initial cell capacity for the bene? t of increased capacity retention over the life of the battery. a reduced ? oat voltage also minimizes swelling in prismatic and polymer cells, and avoids open cid (pressure fuse) in cylindrical cells. battery charge current, charge timeout and end-of-charge indication parameters are set with external components. additional features include shorted cell detection, tempera- ture quali? ed charging and overvoltage protection. the ltc4001-1 is available in a low pro? le (0.75mm) 16-lead (4mm 4mm) qfn package. 2a single cell li-ion battery charger n low power dissipation n 2a maximum charge current n no external mosfets, sense resistor or blocking diode required n remote sensing at battery terminals n programmable charge termination timer n preset 4.1v float voltage with 0.5% accuracy n 4.1v float voltage improves battery life and high temperature safety margin n programmable charge current detection/ termination n automatic recharge n thermistor input for temperature quali? ed charging n compatible with current limited wall adapters n low pro? le 16-lead (4mm 4mm) qfn package n handheld battery-powered devices n handheld computers n charging docks and cradles n digital cameras n smart phones l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. power loss vs v bat charging (pwm mode) v bat (v) 3 total application circuit power dissipation (w) 0.75 1.00 1.25 4 40011 ta01b 0.50 0.25 0 3.25 3.5 3.75 4.25 v in = 5v 2a charger + prog en fault ntc chrg pgnd pv in v insense bat batsens idet timer 274 0.22f 10f 40011 ta01a 4.1v li-ion 10f v in 4.5v to 5.5v 0.1f ss sw sense ltc4001-1 1.5h gndsens
ltc4001-1 2 40011fa pin configuration absolute maximum ratings pv in , v insense t < 1ms, dc < 1% .................................... ?0.3v to 7v steady state ............................................. ?0.3v to 6v sw, sense, bat, batsens, ss, fault, chrg, en, ntc, prog, idet, timer voltage ........................ ? 0.3v to 6v operating temperature range (note 3) .. ?40c to 85c operating junction temperature (note 5) ................................................ ?40c to 125c storage temperature range .................. ?65c to 125c (note 1) 16 15 14 13 5 6 7 8 top view 17 uf package 16-lead (4mm 4mm) plastic qfn 9 10 11 12 4 3 2 1bat sense pgnd gndsens prog ntc fault v insense batsens timer ss idet sw en chrg pv in t jmax = 125c, en r rg r e reer cnn n n n n n n c nene rge c en n r engnen
ltc4001-1 3 40011fa electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: operation with current limited wall adapters is allowed down to the undervoltage lockout threshold. note 3: the ltc4001e-1 is guaranteed to meet performance speci? ca- tions from 0c to 85c. speci? cations over the C 40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v in = 5v, v en = 0v, r prog = 549, r idet = 549, unless otherwise speci? ed. symbol parameter conditions min typ max units f osc oscillator frequency 1.3 1.5 1.7 mhz d maximum duty factor 100 % r pfet r ds(on) of p-channel mosfet measured from pv in to sw 127 m r nfet r ds(on) of n-channel mosfet measured from sw to pgnd 121 m t timer timer accuracy c timer = 0.22f 10 % v en enable input threshold voltage v en rising 0.6 0.8 1 v 6 v en enable input hysteresis 100 mv v prog prog pin voltage r prog = 549 1.213 v v idet idet pin voltage r idet = 549 1.213 v i idet idet threshold r idet = 549 150 200 250 ma i chrg chrg pin weak pull-down current v chrg = 1v 15 30 50 a v chrg chrg pin output low voltage i chrg = 5ma 0.2 0.4 v v ol fault pin output low voltage 1ma load 0.4 v v oh fault pin output high voltage 1ma load 4.6 v v rechrg recharge battery threshold voltage v float C v rechrg v bat falling 50 100 135 mv t rb recharge filter time constant 4 ms t rechrg recharge time percent of total charge time 50 % t trikl low-battery trickle charge time percent of total charge time, v bat < 2.8v, measured using batsens and gndsens pins 25 % i ss soft-start ramp current v bat < v float C 100mv, v bat across batsens and gndsens pins 6 12.8 16 a v cold ntc pin cold temperature fault threshold from ntc to gndsens pin rising threshold falling threshold 0.74 v insense 0.72 v insense v v v hot ntc pin hot temperature fault threshold from ntc to gndsens pin falling threshold rising threshold 0.29 v insense 0.30 v insense v v v dis ntc disable threshold (falling) from ntc to gndsens pin 0.015 ? v insense 0.02 ? v insense 0.025 ? v insense v 6 v dis ntc disable hysteresis from ntc to gndsens pin 0.01 ? v insense v note 4: t j is calculated from the ambient temperature t a and power dis- sipation p d according to the following formula: t j = t a + (p d ? 37c/w) note 5: this ic includes overtemperature protection that is intended to protect the device during momentary overload. junction temperature will exceed 125c when overtemperature protection is active. continuous operation above the speci? ed maximum operating junction temperature my impair device reliability.
ltc4001-1 4 40011fa typical performance characteristics oscillator frequency vs v in oscillator frequency vs temperature dissipation of figure 8 circuit vs i bat dissipation of figure 8 circuit vs v in prog pin characteristic (v prog vs i prog ) output charging characteristic showing constant current and constant voltage operation trickle charge current vs v bat v float and recharge battery threshold voltage vs temperature (t a = 25c unless otherwise noted) v in (v) 3 percent variation (%) C0.25 0 0.25 4.5 5.5 40011 g01 C0.50 C0.75 C1.00 3.5 4 5 0.50 0.75 1.00 6 v bat = 3.2v v ss = 1v temperature ( c) C50 frequency variation from 25 c (%) 0.4 0.6 0.8 110 40011 g02 0.2 0 C0.2 C30 C10 10 30 50 70 90 130 150 v in = 5v v bat = 3.2v v ss = 1v i bat (ma) 500 total application circuit power dissipation (w) 0.50 0.75 40011 g03 0.25 0 1000 1500 2000 1.25 1.00 v in = 5v v bat = 4v v in (v) 4.25 1.0 1.2 1.4 5.25 40011 g04 0.8 0.6 4.5 4.75 5 5.5 0.4 0.2 0 total application circuit power dissipation (w) i bat = 2a v bat = 4v i bat = 1.5a i bat = 1a i bat = 500ma i prog (ma) 0 0.8 1.0 15 40011 g05 0.6 0.4 510 20 0.2 0 1.2 v prog (v) v in = 5v v bat = 3.2v v bat = 4v v bat = 3.5v v bat = 3.7v v bat (v) 0 0 i bat (a) 0.5 1.0 1.5 2.0 0.5 1 1.5 2 40011 g06 2.5 3 3.5 4 v bat (v) 0 40 i bat (ma) 45 50 55 0.5 1 1.5 2 40011 g07 2.5 3 v in = 5.5v v in = 5v v in = 4v v in = 4.5v temperature ( c) 3.9 float and recharge voltages (v) 4.0 4.1 4.2 C10 30 70 110 40011 g08 150 C30 C50 10 50 90 130 v float v recharge (v bat falling)
ltc4001-1 5 40011fa typical performance characteristics soft-start (pwm mode) idet threshold vs r idet for r prog = 549 chrg pin temperature fault behavior (detail) pin functions bat (pin 1): battery charger output terminal. connect a 10f ceramic chip capacitor between bat and pgnd to keep the ripple voltage small. sense (pin 2): internal sense resistor. connect to ex- ternal inductor. pgnd (pin 3): power ground. gndsens (pin 4): ground sense. connect this pin to the negative battery terminal. gndsens provides a kelvin connection for pgnd and must be connected to pgnd schematically. sw (pin 5): switch node connection. this pin connects to the drains of the internal main and synchronous power mosfet switches. connect to external inductor. en (pin 6): enable input pin. pulling the en pin high places the ltc4001-1 into a low power state where the bat drain current drops to less than 3a and the supply current is reduced to less than 50a. for normal opera- tion, pull the pin low. chrg (pin 7): open-drain charge status output. when the battery is being charged, chrg is pulled low by an internal n-channel mosfet. when the charge current drops below the idet threshold (set by the r idet programming resistor) for more than 5milliseconds, the n-channel mosfet turns off and a 30a current source is connected from chrg to ground. (this signal is latched and is reset by initiating a new charge cycle.) when the timer runs out or the input supply is removed, the current source will be disconnected and the chrg pin is forced to a high impedance state. a temperature fault causes this pin to blink. pv in (pin 8): positive supply voltage input. this pin con- nects to the power devices inside the chip. v in ranges from 4v to 5.5v for normal operation. operation down to the undervoltage lockout threshold is allowed with cur- rent limited wall adapters. decouple with a 10f or larger surface mounted ceramic capacitor. v insense (pin 9): positive supply sense input. this pin connects to the inputs of all input comparators (uvl, v in to v bat ). it also supplies power to the controller portion of this chip. when the batsens pin rises to within 30mv of v insense , the ltc4001-1 enters sleep mode, dropping i in to 50a. tie this pin directly to the terminal of the pv in decoupling capacitor. fault (pin 10): battery fault. this pin is a logic high if a shorted battery is detected or if a temperature fault is detected. a temperature fault occurs with the temperature monitor circuit enabled and the thermistor temperature is either below 0c or above 50c (typical). 0 input current (i in ) 0.5a/div inductor current (i l ) 0.5a/div soft-start voltage (v ss ) 1v/div en pin (v en ) 5v/div 0 0 0 2ms/div v bat = 3.5v v in = 5v 40011 g09 r idet () 300 idet (ma) 200 250 300 1100 40011 g10 150 100 0 500 700 900 400 1200 600 800 1000 50 400 350 chrg 1v/div time (20s/div) 40011 g11
ltc4001-1 6 40011fa pin functions ntc (pin 11): input to the ntc (negative temperature coef? cient) thermistor temperature monitoring circuit. under normal operation, tie a thermistor from the ntc pin to the gndsens pin and a resistor of equal value from ntc to v in . when the voltage on this pin is above 0.74v in (cold, 0c) or below 0.29v in (hot, 50c), charging is disabled and the chrg pin blinks. when the voltage on ntc comes back between 0.74v in and 0.29v in , the timer continues where it left off and charging resumes. there is approximately 3c of temperature hysteresis associated with each of the input comparators. if the ntc function is not used connect the ntc pin to gndsens. this will disable all of the ntc functions. ntc should never be pulled above v in . prog (pin 12): charge current program. the r prog resistor connects from this pin to gndsens, setting the current: r prog = 1.110k i bat(amp s) where i bat is the high rate battery charging current. idet (pin 13): charge rate detection threshold. connect- ing a resistor, r idet to gndsens programs the charge rate detection threshold. if r idet = r prog , chrg provides an i bat /10 indication. for other thresholds see the applica- tions information section. ss (pin 14): soft-start/compensation. provides soft-start function and compensation for the ? oat voltage control loop and compensation for the charge current control loop. tie a soft-start/compensation capacitor between this pin and gndsens. timer (pin 15): timer capacitor. the timer period is set by placing a capacitor, c timer , to gndsens. set c timer to: c timer = time (hrs) ? 0.0733 (f) where time is the desired charging time. connect this pin to idet to disable the timer. connect this pin to gndsens to end battery charging when i bat drops below the idet charge rate threshold. batsens (pin 16): battery sense input. an internal resistor divider sets the ? nal ? oat voltage at this pin. the resistor divider is disconnected in sleep mode or when en = h to reduce the battery drain current. connect this pin to the positive battery terminal. exposed pad (pin 17): ground. this pin must be soldered to the pcb ground (pgnd) for electrical contact and rated thermal performance.
ltc4001-1 7 40011fa block diagram battery overvoltage comparator voltage reference + C undervoltage comparator float voltage error amp recharge comparator low-battery comparator shutdown comparator overcurrent comparator current reversal comparator + C + C charge current error amp prog error amp prog short comparator + C idet comparator + C 1.2v 150mv gndsens 40011 bd + C + C soft-start copmparator + C 1.1v 1.2v low current v in good recharge discharge ss prog shorted ss low overvoltage chip over temp chip overtemp comparator connect pwm on trickle on overcurrent shutdown low battery + C + C + C 4 prog idet 12 13 gnd 17 50ma bat 9 v insense 16 batsens sense 2 sw 5 + C 1 + C + C pgnd driver pwm comparator oscillator q s ss rd 3 pv in 8 11 clk ramp + C tfault ntc ntc comparator 15 timer timer 10 fault logic fault 7 chrg chrg 6 en en 14 ss
ltc4001-1 8 40011fa operation the ltc4001-1 is a constant current, constant voltage li-ion battery charger based on a synchronous buck architecture. low power dissipation makes continuous high rate (2a) battery charging practical. the battery dc charge current is programmed by a resistor r prog (or a dac output current) at the prog pin. the ? nal battery ? oat voltage is internally set to 4.1v. charging begins when the v in voltage rises above the uvlo level (approximately 2.75v), v in is 250mv greater than the battery voltage and en is low. at the beginning of the charge cycle, if the battery voltage is less than the trickle charge threshold, 3v, the charger goes into trickle charge mode and delivers approximately 50ma to the bat- tery using a linear charger. if the battery voltage stays low for more than one quarter of the charge time, the battery is considered faulty, the charge cycle is terminated and the fault pin produces a logic high output. when the battery voltage exceeds the trickle charge threshold, the low rate linear charger is turned off and the high rate pwm charger ramps up (based on the ss pin capacitance) reaching its full-scale constant current (set via the prog pin). when the battery approaches the ? oat voltage, the charge current will start to decrease. when the charge current drops below the charge rate detec- tion threshold (set via the idet pin) for more than 5ms, an internal comparator turns off the internal pull-down n-channel mosfet at the chrg pin, and connects a weak current source (30a typical) to ground to indicate a near end-of-charge condition. total charge time is set by an external capacitor connected to the timer pin. after timeout occurs, the charge cycle is terminated and the chrg pin is forced to a high impedance state. to restart the charge cycle, remove and reapply the input voltage, or momentarily shut the charger down via the en pin. also, a new charge cycle will begin if the bat- tery voltage drops below the recharge threshold voltage (100mv below the ? oat voltage). a recharge cycle lasts only one-half of the normal charge time. a negative temperature coef? cient (ntc) thermistor located close to the battery pack can be used to monitor battery temperature and suspend charging when battery tempera- ture is outside the 0c to 50c window. a temperature fault drives the fault pin high and makes the chrg pin blink. when the input voltage (v in ) is present, the charger can be shut down by pulling the en pin up. idet blanking the idet comparator provides an end-of-charge indication by sensing when battery charge current is less than the idet threshold. to prevent a false end-of-charge indication from occurring during soft-start, this comparator is blanked until the battery voltage approaches the ? oat voltage. automatic battery recharge after the charge cycle is completed and if both the battery and the input power supply (wall adapter) are still con- nected, a new charge cycle will begin if the battery voltage drops below 4v due to self-discharge or external loading. this will keep the battery near maximum capacity at all times without manually restarting the charge cycle. in some applications such as battery charging in gprs cellphones, large load current transients may cause battery voltage to momentarily drop below the recharge threshold. to prevent these transients from initiating a recharge cycle when it is not needed, the output of the recharge compara- tor is digitally quali? ed. only if the battery voltage stays below the recharge threshold for at least 4ms will battery recharging occur. (gprs quali? cation is available even if timeout is disabled.) undervoltage lockout and automatic shutdown internal undervoltage lockout circuits monitor v in and keep the charger circuits shut down until v in rises above the undervoltage lockout threshold (3v). the uvlo has a built-in hysteresis of 100mv. furthermore, to protect against reverse current, the charger also shuts down if v in is less than v bat . if automatic shutdown is tripped, v in must increase to more than 250mv above v bat to allow charging.
ltc4001-1 9 40011fa operation overvoltage, chip overtemperature and short-circuit current protection the ltc4001-1 includes overvoltage, chip overtemperature and several varieties of short-circuit protection. a comparator turns off both chargers (high rate and trickle) if battery voltage exceeds the ? oat voltage by ap- proximately 5%. this may occur in situations where the battery is accidentally disconnected while battery charging is underway. a comparator continuously monitors on-chip temperature and will shut off the battery charger when chip temperature exceeds approximately 160c. battery charging will be enabled again when temperature drops to approximately 150c. short-circuit protection is provided in several different ways. first, a hard short on the battery terminals will cause the charge to enter trickle charge mode, limiting charge current to the trickle charge current (typically 50ma). second, pwm charging is prevented if the high rate charge current is programmed far above the 2a maximum recommended charge current (via the prog pin). third, an overcurrent comparator monitors the peak inductor current.
ltc4001-1 10 40011fa soft-start and compensation capacitor selection the ltc4001-1 has a low current trickle charger and a pwm-based high current charger. soft-start is used when- ever the high rate charger is initially turned on, preventing high start-up current. soft-start ramp rate is set by the internal 12.8a pull-up current and an external capacitor. the control range on the ss pin is approximately 0.3v to 1.6v. with a 0.1f capacitor, the time to ramp up to maximum duty cycle is approximately 10ms. the external capacitor on the ss pin also sets the compensa- tion for the current control loop and the ? oat voltage control loop. a minimum capacitance of 10nf is required. charge current and idet programming the ltc4001-1 has two different charge modes. if the battery is severely depleted (battery voltage less than 2.9v) a 50ma trickle current is initially used. if the battery voltage is greater than the trickle charge threshold, high rate charging is used. this higher charge current is programmable and is ap- proximately 915 times the current delivered by the prog pin. this current is usually set with an external resistor from prog to gndsens, but it may also be set with a current output dac connected to the prog pin. the volt- age on the prog pin is nominally 1.213v. for 2a charge current: r prog = 915 ? 1.213v 2 a 554.9 applications information figure 1. programming charge current and idet threshold with a single resistor the idet threshold (a charge current threshold used to determine when the battery is nearly fully charged) is programmed in much the same way as the prog pin, except that the idet threshold is 91.5 times the current delivered by the idet pin. this current is usually set with an external resistor from idet to ground, but it may also be set with a current output dac. the voltage on the prog pin is nominally 1.213v. for 200ma idet current (corresponding to c/10 for a 2ahr battery): r idet = 91.5 ? 1.213v 0.2 a 554.9 1.10k programs approximately 100ma and 274 ap- proximately 400ma. for applications where idet is set to one tenth of the high rate charge current, and slightly poorer charger current and idet threshold accuracy is acceptable, the prog and idet pins may be tied together and a single resistor, r1, can program both (figure 1). r1 = 457.5 ? 1.213 i charg e and idet = i charge 10 prog ltc4001-1 idet r1 274 for 2a gndsens 40011 f01
ltc4001-1 11 40011fa applications information the equations for calculating r1 (used in single resistor programming) differ from the equations for calculating r prog and r idet (2-resistor programming) and re? ect the fact that the current from both the idet and prog pins must ? ow through a single resistor r1 when a single programming resistor is used. chrg status output pin when a charge cycle starts, the chrg pin is pulled to ground by an internal n-channel mosfet which is capable of driving an led. when the charge current drops below the end-of-charge (idet) threshold for at least 4ms, and the battery voltage is close to the ? oat voltage, the n-channel mosfet turns off and a weak 30a current source to ground is connected to the chrg pin. this weak pull-down remains until the charge cycle ends. after charging ends, the pin will become high impedance. by using two different value resistors, a microprocessor can detect three states from this pin (charging, end-of-charge and charging stopped). see figure 2. to detect the charge mode, force the digital output pin, out, high and measure the voltage on the chrg pin. the n-channel mosfet will pull the pin low even with a 2k pull-up resistor. once the charge current drops below the end-of-charge threshold, the n-channel mosfet is turned off and a 30a current source is connected to the chrg pin. the in pin will then be pulled high by the 2k resistor connected to out. now force the out pin into a high impedance state, the current source will pull the pin low through the 390k resistor. when charging stops, the chrg pin changes to a high impedance state and the 390k resistor will then pull the pin high to indicate charg- ing has stopped. charge termination battery charging may be terminated several different ways, depending on the connections made to the timer pin. for time-based termination, connect a capacitor between the timer pin and gndsens (c timer = time(hrs) 0.0733f). charging may be terminated when charge current drops below the idet threshold by tying timer to gndsens. finally, charge termination may be defeated by tying timer to idet. in this case, an external device can terminate charging by pulling the en pin high. battery temperature detection when battery temperature is out of range (either too hot or too cold) charging is temporarily halted and the fault pin is driven high. in addition, if the battery is still charg- ing at a high rate (greater than the idet current) when a temperature fault occurs, the chrg pin nmos turns on and off at approximately 50khz, alternating between a high and low duty factor at an approximate rate of 1.5hz (figure 3). this provides a low rate visual indication (1.5hz) when driving an led from the chrg pin while providing a fast temperature fault indication (20s typical) to a mi- croprocessor by tying the chrg pin to an interrupt line. serrations within this pulse are typically 500ns wide. figure 2. microprocessor interface figure 3. chrg temperature fault waveform ltc4001-1 v in v dd in out processor chrg r2 2k r1 390k 40011 f02 20s 40011 f03 667ms
ltc4001-1 12 40011fa applications information the battery temperature is measured by placing a negative temperature coef? cient (ntc) thermistor close to the bat- tery pack. to use this feature, connect the ntc thermistor, r ntc , between the ntc pin and gndsens and the resistor, r nom , from the ntc pin to v insense . r nom should be a 1% resistor with a value equal to the value of the chosen ntc thermistor at 25c. the ltc4001-1 goes into hold mode when the resistance, r hot , of the ntc thermistor drops to 0.41 times the value of r nom . for instance for r ntc = 10k. (the value for a vishay nths0603n02n1002j thermistor at 25c) hold occurs at approximately 4.1k, which occurs at 50c. the hold mode freezes the timer and stops the charge cycle until the thermistor indicates a return to a valid temperature. as the temperature drops, the resistance of the ntc thermistor rises. the ltc4001-1 is designed to go into hold mode when the value of the ntc thermistor increases to 2.82 times the value of r nom . this resistance is r cold . for the vishay 10k thermistor, this value is 28.2k, which corresponds to approximately 0c. the hot and cold comparators each have approximately 3c of hysteresis to prevent oscillation about the trip point. grounding the ntc pin disables the ntc function. thermistors the ltc4001-1 ntc trip points were designed to work with thermistors whose resistance temperature characteristics follow vishay dales r-t curve 2. however, any thermis- tor whose ratio of r cold to r hot is about 7 will also work (vishay dale r-t curve 2 shows a ratio of r cold to r hot of 2.815/0.4086 = 6.89). power conscious designs may want to use thermistors whose room temperature value is greater than 10k. vishay dale has a number of values of thermistor from 10k to 100k that follow the r-t curve 1. using these as indicated in the ntc thermistor section will give temperature trip points of approximately 3c and 47c, a delta of 44c. this delta in temperature can be moved in either direction by changing the value of r nom with respect to r ntc . increasing r nom will move the trip points to higher temperatures. to calculate r nom for a shift to lower temperature for example, use the following equation: r nom = r cold 2.815 ?r ntc at 25 c where r cold is the resistance ratio of r ntc at the desired cold temperature trip point. if you want to shift the trip points to higher temperatures use the following equation: r nom = r hot 0.4086 ?r ntc at 25 c where r hot is the resistance ratio of r ntc at the desired hot temperature trip point. here is an example using a 100k r-t curve 1 thermistor from vishay dale. the difference between trip points is 44c, from before, and we want the cold trip point to be 0c, which would put the hot trip point at 44c. the r nom needed is calculated as follows: r nom = r cold 2.815 ?r ntc at 25 c = 3.266 2.815 ? 100k = 116k the nearest 1% value for r nom is 115k. this is the value used to bias the ntc thermistor to get cold and hot trip points of approximately 0c and 44c respectively. to extend the delta between the cold and hot trip points a resistor, r1, can be added in series with r ntc (see figure 4). the values of the resistors are calculated as follows: r nom = r cold ?r hot 2.815 ? 0.4086 r1 = 0.4086 2.815 ? 0.4086 ?r cold ?r hot () ?r hot
ltc4001-1 13 40011fa applications information where r nom is the value of the bias resistor, r hot and r cold are the values of r ntc at the desired temperature trip points. continuing the example from before with a desired hot trip point of 50c: r nom = r cold ?r hot 2.815 ? 0.4086 = 100k ? 3.2636 ? 0.3602 () 2.815 ? 0.4086 = 120.8k, 121k is nearest 1% r1 = 100k ? 0.4086 2.815 ? 0.4086 ? 3.266 ? 0.3602 () ? 0.3602 = 13.3k, 13.3k is nearest 1% the ? nal solution is as shown if figure 4 where r nom = 121k, r1 = 13.3k and r ntc = 100k at 25c. input and output capacitors the ltc4001-1 uses a synchronous buck regulator to provide high battery charging current. a 10f chip ceramic capacitor is recommended for both the input and output capacitors because it provides low esr and esl and can handle the high rms ripple currents. however, some high q capacitors may produce high transients due to self-resonance under some start-up conditions, such as connecting the charger input to a hot power source. for more information, refer to application note 88. 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 1.5mhz 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 the output capacitor is 0.1 and the battery impedance is raised to 2 with a bead or inductor, only 5% of the ripple current will ? ow in the battery. similar techniques may also be applied to minimize emi from the input leads. figure 4. extending the delta temperature too cold ltc4001-1 ntc block too hot 0.29 ? v insense 0.74 ? v insense r nom 121k v insense 0.02 ? v insense ntc enable 40011 f04 C + C + C + r1 13.3k r ntc 100k 9 ntc 11 gndsens 4
ltc4001-1 14 40011fa applications information inductor selection a high (1.5mhz) operating frequency was chosen for the buck switcher in order to minimize the size of the inductor. however, take care to use inductors with low core losses at this frequency. a good choice is the ihlp-2525ah-01 from vishay dale. to calculate the inductor ripple current: i l = v bat ? v bat 2 v i n l? f where v bat is the battery voltage, v in is the input voltage, l is the inductance and f is the pwm oscillator frequency (typically 1.5mhz). maximum inductor ripple current oc- curs at maximum v in and v bat = v in /2. peak inductor current will be: i pk = i bat + 0.5 ? 6 i l where i bat is the maximum battery charging current. when sizing the inductor make sure that the peak current will not exceed the saturation current of the inductors. also, 6 i l should never exceed 0.4(i bat ) as this may in- terfere with proper operation of the output short-circuit protection comparator. 1.5h provides reasonable inductor ripple current in a typical application. with 1.5h and 2a charge current: i l = 2.85v ? 2.85v 2 5.5 v 1.5 h ? 1.5mh z = 0.61a p-p and i pk = 2.31a remote sensing for highest ? oat voltage accuracy, tie gndsens and batsens directly to the battery terminals. in a similar fash- ion, tie bat and pgnd directly to the battery terminals. this eliminates ir drops in the gndsens and batsens lines by preventing charge current from ? owing in them. operation with a current limited wall adapter wall adapters with or without current limiting may be used with the ltc4001-1, however, lowest power dissipation battery charging occurs with a current limited wall adapter. to use this feature, the wall adapter must limit at a current smaller than the high rate charge current programmed into the ltc4001-1. for example, if the ltc4001-1 is programmed to charge at 2a, the wall adapter current limit must be less than 2a. to understand operation with a current limited wall adapter, assume battery voltage, v bat , is initially below v trikl , the trickle charge threshold (figure 5). battery charging begins at approximately 50ma, well below the wall adapter current limit so the voltage into the ltc4001-1 (v in ) is the wall adapters rated output voltage (v adapter ). battery voltage rises eventually reaching v trikl . the linear charger shuts off, the pwm (high rate) charger turns on and a soft- start cycle begins. battery charging current rises during the soft-start cycle causing a corresponding increase in wall adapter load current. when the wall adapter reaches current limit, the wall adapter output voltage collapses and the ltc4001-1 pwm charger duty cycle ramps up to 100% (the topside pmos switch in the ltc4001-1 buck regulator stays on continuously). as the battery voltage approaches v float , the ? oat voltage error ampli? er com- mands the pwm charger to deliver less than i limit . the wall adapter exits current limit and the v in jumps back up
ltc4001-1 15 40011fa applications information to v adapter . battery charging current continues to drop as the v bat rises, dropping to zero at v float. because the voltage drop in the ltc4001-1 is very low when charge current is highest, power dissipation is also very low. thermal calculations (pwm and trickle charging) the ltc4001-1 operates as a linear charger when condition- ing (trickle) charging a battery and operates as a high rate buck battery charger at all other times. power dissipation should be determined for both operating modes. for linear charger mode: p d = (v in C v bat ) ? i trikl + v in ? i in where i in is v in current consumed by the ic. worst-case dissipation occurs for v bat = 0, maximum v in , and maximum quiescent and trickle charge current. for example with 5.5v maximum input voltage and 65ma worst case trickle charge current, and 2ma worst case chip quiescent current: p d = (5.5 C 0) ? 65ma + 5.5 ? 2ma = 368.5mw ltc4001-1 power dissipation is very low if a current limited wall adapter is used and allowed to enter current limit. when the wall adapter is in current limit, the voltage drop across the ltc4001-1 charger is: v drop = i limit ? r pfet where i limit is the wall adapter current limit and r pfet is the on resistance of the topside pmos switch. the total ltc4001-1 power dissipation during current limited charging is: p d = (v bat + v drop ) ? (i in + i p ) + v drop ? i limit where i in is the chip quiescent current and i p is total cur- rent ? owing through the idet and prog programming pins. maximum dissipation in this mode occurs with the highest v bat that keeps the wall adapter in current limit (which is very close to v float ), highest quiescent current i in , highest pmos on resistance r pfet , highest i limit and highest programming current i p . assume the ltc4001-1 is programmed for 2a charging and 200ma idet and that a 1.5a wall adapter is being used: i limit = 1500ma, r pfet = 127m, i in = 2ma, i p = 4ma and v bat v float = 4.141v then: v drop = 1500ma ? 127m = 190.5mv and: p d = (4.141v + 0.1905v) ? (2ma + 4ma) + 0.1905v ? 1500ma = 312mw power dissipation in buck battery charger mode may be estimated from the dissipation curves given in the typical performance characteristics section of the data sheet. this will slightly overestimate chip power dissipation because it assumes all loss, including loss from external components, occurs within the chip. figure 5. charging characteristic linear charging v adapter v in v trikl v float 40011 f05 v bat i bat i trickle wall adapter in current limit v bat + v drop i limit pwm charging
ltc4001-1 16 40011fa applications information insert the highest power dissipation ? gure into the following equation to determine maximum junction temperature: t j = t a + (p d ? 37c/w) the ltc4001-1 includes chip overtemperature protection. if junction temperature exceeds 160c (typical), the chip will stop battery charging until chip temperature drops below 150c. using the ltc4001-1 in applications without a battery the ltc4001-1 is normally used in end products that only operate with the battery attached (figure 6). under these conditions the battery is available to supply load transient currents. for inde? nite operation with a powered wall adapter there are only two requirementsthat the aver- age current drawn by the load is less than the high rate charge current, and that v bat stays above the trickle charge threshold when the load is initially turned on and during other load transients. when making this determination take into account battery impedance. if battery voltage is less than the trickle charge threshold, the system load may be turned off until v bat is high enough to meet these conditions. the situation changes dramatically with the battery re- moved (figure 7). since the battery is absent, v bat begins at zero when a powered wall adapter is ? rst connected to the battery charger. with a maximum load less than the ltc4001-1 trickle charge current , battery voltage will ramp up until v bat crosses the trickle charge threshold. when this occurs, the ltc4001-1 switches over from trickle charge to high rate (pwm) charge mode but initially delivers zero current (because the soft-start pin is at zero). battery volt- age drops as a result of the system load, crossing below the trickle charge threshold. the charger re-enters trickle charge mode and the battery voltage ramps up again until the battery charger re-enters high rate mode. the soft-start voltage is slightly higher this time around (than in the previous pwm cycle). every successive time that the charger enters high rate (pwm) charge mode, the soft-start pin is at a slightly higher voltage. eventually high rate charge mode begins with a soft-start voltage that causes the pwm charger to provide more current than the system load demands, and v bat rapidly rises until the ? oat voltage is reached. for battery-less operation, system load current should be restricted to less than the worst case trickle charge current (preferably less than 30ma) when v bat is less than 3.15v (through an undervoltage lockout or other means). above v bat = 3.15v, system load current less than or equal to the high rate charge current is allowed. if operation without a battery is required, additional low-esr output ? ltering improves start-up and other load transients. battery-less start-up is also improved if a 10k resistor is placed in series with the soft-start capacitor. figure 6. typical application + wall adapter ltc4001-1 battery charger system load li-ion battery 40011 f06
ltc4001-1 17 40011fa applications information figure 7. battery-less start-up 024681012 time (ms) 14 16 18 20 22 24 4 3 2 1 0 v bat (v) 024681012 time (ms) 14 16 18 20 22 24 500 250 0 v ss (mv) 024681012 time (ms) 40011 f07 14 16 18 20 22 24 pwm charge trickle charge
ltc4001-1 18 40011fa applications information layout considerations switch rise and fall times are kept under 5ns for maximum ef? ciency. to minimize radiation, the sw pin and input bypass capacitor leads (between pv in and pgnd) should be kept as short as possible. a ground plane should be used under the switching circuitry to prevent interplane coupling. the exposed pad must be connected to the ground plane for proper power dissipation. the other paths contain only dc and/or 1.5mhz tri-wave ripple current and are less critical. with the exception of the input and output ? lter ca- pacitors (which should be connected to pgnd) all other components that return to ground should be connected to gndsens. recommended components manufacturers for a list of recommend component manufacturers, contact the linear technology application department. figure 8. 2a li-ion battery charger with 3hr timer, temperature quali? cation, soft-start, remote sensing and c/10 indication + prog en fault to p from p ntc chrg pgnd pv in v insense bat batsens idet timer r4 549 c2 0.22f c3 0.1f l1: vishay dale ihlp-2525ah-01 r3: ntc vishay dale nths0603n02n1002j c4 10f 40011 f08 2ahr 4.1v li-ion c1 10f d1 led v in 4.5v to 5.5v ss sw sense ltc4001-1 l1 1.5h gndsens r2 1k r1 10k r3 10k at 25 c r5 549
ltc4001-1 19 40011fa 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description uf package 16-lead plastic qfn (4mm 4mm) (reference ltc dwg # 05-08-1692) 4.00 0.10 (4 sides) note: 1. drawing conforms to jedec package outline mo-220 variation (wggc) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.55 0.20 16 15 1 2 bottom view?exposed pad 2.15 0.10 (4-sides) 0.75 0.05 r = 0.115 typ 0.30 0.05 0.65 bsc 0.200 ref 0.00 ? 0.05 (uf16) qfn 10-04 recommended solder pad pitch and dimensions 0.72 0.05 0.30 0.05 0.65 bsc 2.15 0.05 (4 sides) 2.90 0.05 4.35 0.05 package outline pin 1 notch r = 0.20 typ or 0.35 45 chamfer
ltc4001-1 20 40011fa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2007 lt 1207 rev a ? printed in usa related parts part number description comments lt ? 1511 3a constant-current/constant-voltage battery charger high ef? ciency, minimum external components to fast charge lithium, nimh and nicd batteries, 24-lead so package lt1513 sepic constant or programmable current/constant- voltage battery charger charger input voltage may be higher, equal to or lower than battery voltage, 500khz switching frequency, dd pak and to-220 packages lt1571 1.5a switching charger 1- or 2-cell li-ion, 500khz or 200khz switching frequency, termination flag, 16- and 28-lead ssop packages ltc1729 li-ion battery charger termination controller trickle charge preconditioning, temperature charge quali? cation, time or charge current termination, automatic charger and battery detection, and status output, ms8 and so-8 packages lt1769 2a switching charger constant-current/constant-voltage switching regulator, input current limiting maximizes charge current, 20-lead tssop and 28-lead ssop packages ltc4001 monolithic 2a switchmode synchronous li-ion battery charger 4.2v float voltage, standalone, 4v v in 5.5v, 6v max , 7v transient, 1.5mhz, ef? ciency > 90%, 4mm 4mm qfn-16 package ltc4002 standalone li-ion switch mode battery charger complete charger for 1- or 2-cell li-ion batteries, onboard timer terminati on, up to 4a charge current, 10-lead dfn and so-8 packages ltc4006 small, high ef? ciency, fixed voltage li-ion battery charger with termination complete charger for 2-, 3- or 4-cell li-ion batteries, ac adapter current limit and thermistor sensor, 16-lead narrow ssop package ltc4007 high ef? ciency, programmable voltage battery charger with termination complete charger for 3- or 4-cell li-ion batteries, ac adapter current limit, thermistor sensor and indicator outputs, 24-lead ssop package ltc4008 4a, high ef? ciency, multi-chemistry battery charger complete charger for 2- to 6-cell li-ion batteries or 4- to 18-cell nickel batteries, up to 96% ef? ciency, 20-lead ssop package

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