general description the max1736 is a simple, low-cost, single-cell lithium-ion (li+) battery charger for small hand-held applica- tions. when accompanied by a current-limited voltage source (such as a wall cube), the max1736 provides simple, accurate charging and termination control for single-cell li+ batteries. the MAX1736EUT42 is preset to a 4.2v battery regulation voltage, while the max1736eut41 is preset to 4.1v. the max1736 initiates charging in one of four ways: battery insertion, charger power-up, battery voltage threshold, and by external manipulation of the en pin. the device features an internal precharge current source that safely charges near-dead cells, as well as input-supply detection that shuts down the max1736 when the supply is removed to minimize battery current drain. the max1736 accepts input voltages up to 22v, mak- ing it compatible with a wide range of input supplies. it has a single control input yet offers stand-alone and microprocessor-controlled operation. the max1736 is packaged in a small sot23-6 package. an evaluation kit (ev kit) is available to reduce design time. ________________________applications single-cell li+ portable applicationswireless handsets personal digital assistants digital cameras small hand-held equipment self-charging battery packs cradle chargers features ? small 6-pin sot23 package ? stand-alone or ?-controlled operation ? 0.5% voltage set-point accuracy ? lowest power dissipation ? low 4.7v min input voltage ? top-off charging to achieve full battery capacity ? no inductor required ? safely precharges near-dead cells ? automatic power-down when input powerremoved note: requires special solder temperature profile described in the absolute maximum ratings section. max1736 sot23, single-cell li+ battery charger for current-limited supply ________________________________________________________________ maxim integrated products 1 gate en gnd 16 batt 5 ct in max1736 sot23 top view 234 pin configuration current-limited voltage source gate batt battery gnd inen ct on off max1736 pfet typical operating circuit 19-1662; rev 1; 10/00 evaluation kit available ordering information part temp. range pin-package sot mark MAX1736EUT42-t -40 c to +85 c 6 sot23-6 aaho max1736eut41-t -40 c to +85 c 6 sot23-6 aanc for price, delivery, and to place orders, please contact maxim distribution at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. downloaded from: http:///
max1736 sot23, single-cell li+ battery charger for current-limited supply 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in, gate to gnd....................................................-0.3v to +26v batt, en, ct to gnd ..............................................-0.3v to +6v gate to in................................................................-6v to +0.3v gate continuous current.................................-10ma to +10ma continuous power dissipation (t a = +70 c) (note 1) 6-pin sot23 (derate 8.1mw/ c above +70 c) .............0.65w operating temperature range ...........................-40? to +85 c storage temperature range ..............................-65? to + 150 c maximum junction temperature ......................................+ 150 c lead temperature (soldering, 10s) (note 2) ...................+300 c electrical characteristics(v in = 10v, v batt = 4.2v for MAX1736EUT42 or 4.1v for max1736eut41, t a = 0 c to +85 c . typical values are at t a = +25 c, unless otherwise noted.) (note 3) parameter conditions min typ max units input voltage (note 4) external p-mosfet off 4.7 22 v fast-charge batt qualificationthreshold batt rising, transition from precharge to fast charge 2.4 2.5 2.65 v fast-charge batt qualificationthreshold hysteresis 70 mv MAX1736EUT42 4.179 4.20 4.221 batt regulation voltage max1736eut41 4.079 4.10 4.121 v batt removal detectionthreshold batt rising 4.875 5.0 5.1 v batt removal detectionthreshold hysteresis 125 mv batt input current, input powerremoved v in v batt - 0.3v 0.1 1 a batt input current, chargerdisabled en = gnd, v batt = 0 to 5v 2 6 a batt input current, whencharging 0.4 0.75 ma precharge source current v batt = 2v 3.5 6 8 ma in input current 0.25 1 ma in detection interval (note 5) c ct = 0.33? 20 s gate source/sink current 75 100 125 a gate drive source current atbattery removal v batt = 5.1v 15 30 60 ma minimum batt bypasscapacitance (note 6) 1.5 f/a en logic high threshold 2v en logic low threshold 0.7 v ct pulldown current 1.6 2 2.4 a note 1: thermal properties are specified with product mounted on pc board with one square-inch of copper area and still air. note 2: this device is constructed using a unique set of packaging techniques that impose a limit on the termal profile the device can be exposed to during solder attach and rework. this limit permits only the use of the solder profiles recommended in the industry stan- dard specification, ipc/jedec j-std-020a, paragraph 7.6, table 3 for the ir/vpr and convention reflow. pre-heating is required. hand or wave soldering is not allowed. downloaded from: http:///
max1736 sot23, single-cell li+ battery charger for current-limited supply _______________________________________________________________________________________ 3 electrical characteristics (continued)(v in = 10v, v batt = 4.2v for MAX1736EUT42 or 4.1v for max1736eut41, t a = 0? to +85? . typical values are at t a = +25 c, unless otherwise noted.) electrical characteristics(v in = 10v, v batt = 4.2v for MAX1736EUT42 or 4.1v for max1736eut41, t a = -40? to +85? , unless otherwise noted.) (note 3) parameter conditions min typ max units ct pullup current -12 -10 -8 a minimum on-time c ct = 0.33? 165 ms minimum off-time c ct = 0.33? 33 ms en pullup resistance 175 350 725 k parameter conditions min max units input voltage (note 4) external p-mosfet off 4.7 22 v fast-charge batt qualificationthreshold batt rising, transition from precharge to fast charge 2.4 2.65 v MAX1736EUT42 4.158 4.242 v batt regulation voltage max1736eut41 4.058 4.142 batt removal detectionthreshold batt rising 4.85 5.125 v batt input current, input powerremoved v in v batt - 0.3v 1 a batt input current, chargerdisabled en = gnd, v batt = 0 to 5v 6 a batt input current, whencharging 0.75 ma precharge source current v batt = 2v 3 8 ma in input current 1m a gate source/sink current 60 140 a gate drive source current atbattery removal v batt = 5.1v 10 90 ma en logic high threshold 2 v en logic low threshold 0.7 v ct pulldown current 1.5 2.5 ? ct pullup current -12 -8 ? en pullup resistance 170 725 k note 3: all devices are 100% production tested at t a = +25 c. limits over the operating temperature range are guaranteed by design. note 4: the input voltage range is specified with the external pfet off. when charging, the pfet turns on and the input voltage (theoutput voltage of the constant-current power source) drops to very near the battery voltage. when the pfet is on, in may be as low as 2.5v. note 5: every 20s (for ct = 0.33?) the max1736 turns off the external p-channel mosfet and samples in to determine if inputpower is present. if input power is removed, the charger shuts down. note 6: for design guidance, not tested. downloaded from: http:///
max1736 sot23, single-cell li+ battery charger for current-limited supply 4 _______________________________________________________________________________________ 0.1 1 10 minimum on/off-times vs. c ct max1736 toc01 c ct ( f) minimum on/off-time (ms) 10 100 1000 10,000 minimum off-time minimum on-time -0.20 -0.15 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 -40 -15 10 35 60 85 batt regulation voltage deviation vs. temperature max1736-02 temperature (?) batt voltage deviation (%) 5.1 5.35.2 5.55.4 5.75.6 5.8 precharge current vs. input voltage max1736-03 v in (v) precharge current (ma) 4 9 14 19 24 v batt = 2v v batt = 1v v batt = 0 precharge current (ma) 0.1 1 10 input detection interval vs. c ct max1736 toc04 c ct (?) input detection interval (s) 1000 1 10 100 oa ov v batt 200mv/div i in 1a/div i in 5v/div v gate 10v/div typical operating waveforms max1736 toc05 10ms/div ac-coupled pfet off pfet on typical operating characteristics (t a = +25 c, unless otherwise noted.) downloaded from: http:///
max1736 sot23, single-cell li+ battery charger for current-limited supply _______________________________________________________________________________________ 5 pin description pin name description 1i n input voltage from current-limited voltage source (22v max). bypass to gnd with a 0.1 f capacitor. the charging current is set by the current limit of the external power supply. 2 gate gate drive for external pmos pass element. the pmos device should have a v gs threshold of 2.5v or less (see selecting external components) . 3 gnd ground. connect the battery s negative terminal to gnd. 4e n logic-level enable input. pull low to disable the max1736. en is internally pulled up to v batt + 100mv through 350k , but draws no current from batt. 5c t charge time control. sets the minimum on-time, minimum off-time, and the in detection interval.place a 0.33 f capacitor between ct and gnd for most applications (see selecting external components ). 6 batt cell voltage monitor input, precharge current output, and max1736 power source. connect battto the positive terminal of a single li+ cell. bypass batt with a capacitor to gnd (1.5 f per amp of charge current). detailed description the max1736 provides a simple, safe, low-cost methodof charging a single-cell li+ battery with nearly no heat generation. combined with a current-limited voltage source, the max1736 provides precharge, fast-charge, and top-off-charge capabilities. after constant-current fast charge, top-off safely finishes charging the battery by pulse-width modulating charge current. the top-off on-time is kept below the electrochemical time constant of the cell. the key advantage of this method is that the charge circuit is small and generates minimal heat while providing a safe method of charging to ensure maximum cell life. figure 1 shows the max1736 func- tional diagram. precharge to protect li+ cells from damage that may occur if fastcharged from a dead state, the max1736 precharges the li+ cell with 6ma at the start of a charging cycle when the cell voltage is below 2.5v. as soon as the cell voltage reaches 2.5v, the max1736 begins fast charging. fast charge in fast-charge mode, the max1736 turns on the exter-nal p-channel mosfet. charging current is set by the current limit of the external supply; current is not regu- lated by the max1736 . the p-channel mosfet is used only as a switch, not as a linear regulator.therefore, the circuit s power dissipation is minimized, permitting rapid charge cycles with almost no heatgeneration. the external power supply should have a specified current limit that matches the desired fast-charge current for the li+ cell. with the p-channel mosfet on, v in will be nearly equal to v batt . to detect that an input supply is con- nected, the max1736 periodically turns the p-channelmosfet off and checks the voltage at in. during fast charge, this occurs once every input detection interval (20s with c ct = 0.33?). during pulsed top-off, input detection occurs more frequently and is continuouswhen the mosfet is off (see selecting external components ). pulsed top-off when the battery approaches full charge, its instanta-neous voltage reaches the batt regulation voltage and pulsed top-off begins. the max1736 uses a hysteretic algorithm with a minimum on- and off-time. cell voltage is sampled with no charging current to minimize errors due to battery and cell protection resistance. if the voltage is below the batt regulation voltage, the p-channel mosfet switches on for a minimum on-time. if, at the end of the minimum on-time, the cell voltage is still below the batt regulation voltage, the switch remains on until the cell voltage reaches the batt reg- ulation voltage. at that point, the p-channel mosfet then switches off for at least the minimum off-time. the minimum on-time is set by ct and should be set below the electrochemical time constant of the cell. a c ct value of 0.33? sets a minimum on-time of 165ms,which is adequate for most li+ batteries. downloaded from: http:///
6 ____________________________________________________________________________________________________ once the switch turns off, it remains off for at least theminimum off-time. after the minimum off-time, the p- channel mosfet turns on if the cell voltage is lower than the batt regulation voltage. a c ct value of 0.33? sets a minimum off-time of 33ms.at the beginning of the pulsed top-off state, charge cur- rent is modulated at approximately an 83% duty cycle. toward the end of top-off, charge current stays off for long periods of time between single on pulses. during these final pulses, the instantaneous cell voltage mayexceed the batt regulation voltage by several hun- dred millivolts, but these pulses are orders of magni- tude shorter than the electrochemical time constant of the li+ cell and do no harm. pulsed top-off charge ends when the cell voltage no longer falls below the batt regulation voltage. figure 2 shows the state machine. selecting external components input power supply one reason the max1736 li+ charger is so compactand simple is that the charging current is set by the external power source, not by the max1736. the p-channel mosfet in figure 3 s application circuit is either on or off, allowing the source to be directly con-nected to the cell or disconnected. therefore, it is important to choose a power supply with the correct current limit for the cell to be charged. in most applica- tions, this will be a small wall cube with an open-circuit output voltage of 5v to 12v, which is specified as cur- rent limited or constant current. some low-cost wall cubes may have poor transientcharacteristics. for these wall cubes, output current may exceed the specified current limit by several times when the load is quickly connected. the max1736 lim- its this current peak by controlling the slew rate of the p-channel mosfet. see c ct and c gate for more information. pmos switch the p-channel mosfet switches the current-limitedsource on and off. because of the intentionally slow switching times and limited slew rate, the max1736 is not particular about the power fet it drives. spec- ifications to consider when choosing an appropriate max1736 sot23, single-cell li+ battery charger for current-limited supply en in in gate in 6ma 4.2v (4.1v)5v ref gnd 0.4v 1.4v 10 a ct 2 a 350k v batt + 100mv state machine batt MAX1736EUT42 (max1736eut41) figure 1. functional diagram downloaded from: http:///
fet are the minimum drain-source breakdown voltageand the minimum turn-on threshold voltage (v gs ). power dissipation during fast charge is approximatelyr dson ? i chg 2 , where i chg is the current limit set by the input power source. the minimum breakdown volt-age (bv ds ) must typically be two times the wall cube s open-circuit voltage. an even larger margin may benecessary if the wall adapter has especially poor tran- sient response. the max1736 can operate with input voltages up to 22v. batt capacitor bypass batt with at least 1.5? per amp of chargecurrent. if the battery is removed while the p-channel mosfet is on, a batt voltage over 5v is quickly sensed, and the fet is immediately turned off. in appli- cations where the cell is removable, very large capaci- tance values may increase transient currents when the cell is replaced. therefore, batt capacitance in excess of 100? should be avoided. for best system performance with large output capacitance, at least 0.47? of the total capacitance should be low-esrceramic. c ct and c gate most applications will use the circuit of figure 3 withc gate = 0.22?, r gate = 100k , and c ct = 0.33?. c gate , r gate , and the internal 100? pull-up and pull- down current sources act to slow the switching of the p-channel mosfet. this prevents a wall cube with poor transient response from subjecting v in to excessive voltage when the p-channel mosfet turns off, and pre-vents excessive current into the battery when the p- channel mosfet turns on. excessive voltage at v in can potentially damage the ic, input capacitor, and thepmos switch. excessive current into the battery can cause errors in the termination process of the max1736 (by raising the instantaneous battery voltage) and may trip the battery s protection circuitry. in applications utilizing a wall cube with poor transientresponse, increase the value of c gate as needed to max1736 sot23, single-cell li+ battery charger for current-limited supply _______________________________________________________________________________________ 7 shutdown fet: off every cycle chargerpower present charger power present charger power removed (from any state) chargerpower present top-off qual fet: off top-off fet: pulsed fast-charge fet: on fast-charge qual fet: off v batt > 4.2v v batt 2.5v v batt < 2.5v v batt < 2.5v in detection interval en disabled fet: off precharge fet: off i out = -6ma (from any state) en figure 2. state machine downloaded from: http:///
max1736 maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 8 _____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2000 maxim integrated products printed usa is a registered trademark of maxim integrated products. further slow switching edges and prevent transientspikes. c ct sets the minimum on-time and off-time according to the following equations: t on(min) = 5 ? 10 5 x c ct t off(min) = 1 ? 10 5 x c ct layout guidelines the max1736 controls the gate slew rate; conse-quently, pc board layout is not as sensitive to noise as a high-frequency switching regulator. in addition, since cell voltage is sensed both during and between high- current pulses, the system is insensitive to ground errors. however, maxim recommends maintaining large ground area and large traces for high-current paths. refer to the max1736evkit for a recommended layout example. chip information transistor count: 1622 0.33 f 0.1 f 100k 0.22 f ct batt gate 2.2 f singleli+ cell gnd in current-limitedwall cube (800ma) fdc638p pfet max1736 figure 3. simple application circuit package information 6lsot.eps sot23, single-cell li+ battery charger for current-limited supply downloaded from: http:///
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