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general description the max1898, with an external pnp or pmos transistor,forms a complete charger for 1-cell lithium-ion (li+) bat- teries. the max1898 provides accurate constant-cur- rent/constant-voltage charging. battery regulation voltage accuracy is ?.75% for optimum battery performance and cycle life. charging current is user set, but is sensed internally so no external current-sense resistor is needed. the max1898 also provides outputs to monitor charge status, presence-of-input power source, and charge cur- rent. additional features include shutdown, optional charge-cycle restart without input-power cycling, selec- table charge termination safety timer, and low-current preconditioning for deeply discharged cells. the max1898 offers the maximum integration and func- tionality in the smallest, most basic application circuit possible. very few external components are required. the max1898 offers two versions to safely charge all li+ battery chemistries. the battery regulation voltage is 4.2v for the max1898eub42 and 4.1v for the max1898eub41. both are available in a 10-pin ultra- thin ?ax package. features ? simple, safe linear charger ? uses low-cost pnp or pmos pass element ? 4.5v to 12v input range ? internal current-sense resistor ? ?.75% voltage accuracy ? programmable charging current ? automatic input power-source detection ? led charge status indicator ? programmable safety timer ? current-sense monitor output ? optional/adjustable auto-restart ? small ?ax package max1898 linear charger for single-cell li+ battery ________________________________________________________________ maxim integrated products 1 ordering information max1898 in ct rstrt gnd en/ok chg cs iset batt drv off on led li+battery sets chargecurrent ct sets charge time output input4.5v to 12v typical operating circuit 19-2295; rev 0; 1/02 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. part temp range pin-package max1898eub42 -40? to +85? 10 ?ax max1898eub41 -40? to +85? 10 ?ax pin configuration 1 23 4 5 10 98 7 6 csdrv gnd batt iset en/ok in max1898 max top view rstrt ct chg applications single-cell li+ powered portablesself-charging battery packs pdas cell phones cradle chargers downloaded from: http:///
max1898 linear charger for single-cell li+ battery 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics(v in = 8v, v batt = 4v, en/ok = open, rset = 2.8k , rstrt = gnd, t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) 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, drv, cs, chg to gnd .....................................-0.3v to +14v batt, en, iset, rstrt, ct to gnd ........................-0.3v to +6v drv to in................................................................-14v to +0.3v in to cs current ....................................................................?a drv continuous current ..................................................?0ma continuous power dissipation (t a = +70?) 10-pin ?ax (derate 5.6mw/? above +70?) ..........444mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) ....................?.+300? parameter conditions min typ max units supply voltage range 4.5 12 v input ok trip point, in rising(v in - v batt ) 45 70 100 mv input ok trip point, in falling(v in - v batt ) 30 55 85 mv v in input ok trip point, in rising 4.0 4.25 4.5 v v in input ok trip point, in falling 3.9 4.15 4.4 v en/ok sink current (when inputpower not ok) v in = 3.9v, v batt = 4v, v en/ok = 0.8v 100 ? en/ok source current (wheninput power ok) v en/ok = 2v 5 10 20 a en/ok logic input high 4.5v v in 12v 2 v en/ok logic input low 4.5v v in 12v 0.6 v done, rstrt = gnd, v batt = 4.1v for max1898eub42 and 4.0v for max1898eub41 40 100 done, rstrt = open, v batt = 4.1v for max1898eub42 and 4.0v for max1898eub41 41 0 en/ok = gnd 4 10 batt input current v in = 4v 3 10 ? v in = v batt = 4v (i in + i cs ) 2 10 ? in, cs input current v in = 12v, (i in + i cs ), done, rstrt = open 2 5 ma voltage loop max1898eub42 4.168 4.2 4.232 voltage-loop set point max1898eub41 4.069 4.1 4.131 v voltage-loop gain ? v drv / ? v batt 51 db max1898eub42 2.394 2.520 2.646 v batt prequal voltage threshold timers running max1898eub41 2.337 2.460 2.583 v drv sink current v drv = v in - 1v, v batt = 3.5v 4 ma drv output resistance 470 downloaded from: http:///
max1898 linear charger for single-cell li+ battery _______________________________________________________________________________________ 3 electrical characteristics (continued)(v in = 8v, v batt = 4v, en/ok = open, rset = 2.8k , rstrt = gnd, t a = 0 c to +85 c , unless otherwise noted. typical values are at t a = +25 c.) parameter conditions min typ max units maximum voltage (v in - v drv )v batt = 3.5v 3.5 7 v v batt restart threshold (as a percentage of voltage-loop setpoint) rstrt = gnd 92 95.25 98 % rstrt internal resistance 100 k current loop internal current-sense resistance in to cs pin-to-pin resistance 50 105 200 m rms charge current 1.4 a current-sense amplifier gain, i set to i in fast charge i cs = 500ma, v set = 1.4v 0.95 1 1.05 ma/a current-sense amplifier gain, i set to i in prequal i cs = 50ma, v iset = 0.14v, v batt = 2v 0.73 1 1.30 ma/a current-loop regulation set point rset = 2.8k , v batt = 3.5v, closed-loop performance 450 500 550 ma current-loop gain ? v drv / ? v iset 26 db i load falling, rset = 2.8k 15 20 25 chg trip threshold (as a percentage of full load current) i load rising, rset = 2.8k 17 22 27 % timer function timer source/sink current v ct = 0.9v 5 a timer accuracy c ct = 100nf for 2 hours, 54 minutes nominal -10 +10 % chg output low current v chg = 1v 4 5 6 ma chg output high leakage v chg = 12v 1 a chg blink rate fault state (50% duty cycle), ct = 100nf 1 1.5 2 hz electrical characteristics(v in = 8v, v batt = 4v, en/ok = open, rset = 2.8k , rstrt = gnd, t a = -40 c to +85 c , unless otherwise noted.) parameter conditions min max units supply voltage range 4.5 12 v input ok trip point, in rising(v in - v batt ) 45 100 mv input ok trip point, in falling(v in - v batt ) 30 85 mv v in input ok trip point, in rising 4.0 4.5 v v in input ok trip point, in falling 3.9 4.4 v en/ok sink current (when inputpower not ok) v in = 3.9v, v batt = 4v, v en/ok = 0.8v 100 ? en/ok source current (when inputpower ok) v en/ok = 2v 5 20 a en/ok logic input high 4.5v v in 12v 2 v en/ok logic input low 4.5v v in 12v 0.6 v downloaded from: http:///
max1898 linear charger for single-cell li+ battery 4 _______________________________________________________________________________________ note 1: specifications to -40 c are guaranteed by design and not production tested. electrical characteristics (continued)(v in = 8v, v batt = 4v, en/ok = open, rset = 2.8k , rstrt = gnd, t a = -40 c to +85 c , unless otherwise noted.) parameter conditions min max units done, rstrt = gnd, v batt = 4.1v for max1898eub42 and 4.0v for max1898eub41 100 done, rstrt = open, v batt = 4.1v for max1898eub42 and 4.0v for max1898eub41 10 en/ok = gnd 10 batt input current v in = 4v 10 ? v in = v batt = 4v (i in + i cs )1 0 a in, cs input current v in = 12v, (i in + i cs ), done, rstrt = open 5 ma voltage loop max1898eub42 4.137 4.263 voltage-loop set point max1898eub41 4.038 4.162 v max1898eub42 2.394 2.646 v batt prequal voltage threshold timers running max1898eub41 2.337 2.583 v drv sink current v drv = v in - 1v, v batt = 3.5v 3.5 ma maximum voltage (v in - v drv )v batt = 3.5v 3 7 v v batt restart threshold (as a percentage of voltage-loop setpoint) rstrt = gnd 92 98 % current loop internal current-sense resistance in to cs pin-to-pin resistance 50 200 m rms charge current 1.4 a current-sense amplifier gain, i set to i in fast charge i cs = 500ma, v set = 1.4v 0.93 1.07 ma/a current-sense amplifier gain, i set to i in prequal i cs = 50ma, v iset = 0.14v, v batt = 2v 0.6 1.50 ma/a current-loop regulation set point rset = 2.8k , v batt = 3.5v, closed-loop performance 440 560 ma i load falling, rset = 2.8k 15 25 chg trip threshold (as a percentage of full load current) i load rising, rset = 2.8k 17 27 % timer accuracy c ct = 100nf for 2 hours, 54 minutes nominal -13 +13 % chg output low current v chg = 1v 3.5 7 ma chg output high leakage v chg = 12v 1 a chg blink rate fault state (50% duty cycle), ct = 100nf 1 2 hz downloaded from: http:///
max1898 linear charger for single-cell li+ battery _______________________________________________________________________________________ 5 0.90 0.940.92 0.980.96 1.00 1.02 -40 85 normalized timer period vs. temperature max1898 toc01 temperature ( c) timer period 10 -15 35 60 normalized to +25 c 0.996 0.9980.997 1.0000.999 1.001 1.002 -40 85 normalized batt regulation voltage vs. temperature max1898 toc02 temperature ( c) batt regulation voltage 10 -15 35 60 normalized to +25 c 40 45 50 55 60 precharge current vs. input voltage max1898 toc03 v in (v) precharge current (ma) 58 9 6 7 10 11 12 iset = 2.8k charging current setfor 500ma 0 0.40.2 0.80.6 1.0 1.2 3.9 4.1 4.0 4.2 4.3 normalized battery current vs. battery voltage max1898 toc04 battery voltage (v) normalized battery current -40 -20 20 0 40 60 -50 0 10050 150 200 0.01 1 0.1 10 100 1000 voltage-loop gain max1898 toc05 frequency (khz) gain (db) phase (deg.) gain phase typical operating characteristics (v in = 5v, v batt = 4v, en/ok = open, rset = 2.8k , rstrt = gnd, t a = +25 c, unless otherwise noted.) downloaded from: http:///
max1898 detailed description the max1898 forms a complete charger for 1-cell li+batteries. it includes precision voltage control (?.75%) to optimize both cell performance and cycle life. factory-set 4.2v (max1898eub42) and 4.1v (max1898eub41) versions charge all common li+ chemistries. externally selectable charge current is sensed internally, eliminating the need for a current- sense resistor. the charger also supplies outputs that indicate charge status ( chg ), the presence of input power (en/ok), and charge-current magnitude (iset).other features include a shutdown control input (en/ok), selectable threshold for charge-cycle restart without cycling input power (rstrt), and a selectable charge termination safety timer. see figure 1. the max1898 initiates fast charge when any of these conditions are met (see figure 6): an external power source is connected and the cellvoltage is above 2.5v. the cell voltage falls to the restart threshold, 4.0v inthe max1898eub42, or 3.9v for the max1898eub41. the ic is reset by driving the en/ok pin low andthen high again. the prequalification cycle ends with the cell reaching2.5v. li+ cells can be damaged when fast-charged from acompletely dead state. a fully discharged cell may indi- cate an abnormal cell condition. as a built-in safety fea- ture, the max1898 prequalifies the cell with 10 percent of the user-programmed fast-charge current at the start of a charge cycle. when the cell voltage rises to 2.5v, the max1898 begins fast-charging. current-limit mode the max1898 regulates charging current by linearlycontrolling an external pmos or pnp transistor. the maximum charging current is programmed by an exter- nal rset resistor connected from iset to gnd. select the rset value based on the following formula: where: i fastchg is in amps and rset is in ohms. the iset pin may also be used to monitor the actualcharging current at any time. the output current from i v r fastchg set = 1400 linear charger for single-cell li+ battery 6 _______________________________________________________________________________________ pin description pin name function 1 in sense input. detects power source; positive side of internal current-sense resistor. 2 chg open-drain led driver. see table 1 for chg output states. 3 en/ok logic-level enable input and input power ok output. hold low to disable charger. float for normaloperation, drive with an open-drain device to utilize both pin functions, or connect through 10k for logic- controlled on/off. see the en/ok (en input, ok output) section for details. 4 iset iset serves two functions. it provides an analog output proportional to the actual charge current. output current from iset is 1ma per amp of battery charging current. the charging current is set by connecting a resistor from iset to ground. see the current-limit mode section. 5c t safety charge timer control. connect timer capacitor to program safety time-out interval; 100nf for approximately three hours. connect to gnd to disable the timer function. 6 rstrt automatic-restart control pin. when tied to gnd, a new charging cycle starts if the cell drops 200mv belowthe battery regulation threshold. the restart threshold may be lowered by connecting a resistor from rstrt to ground. see the reinitiating a charging cycle section . automatic restart is disabled when rstrt is unconnected or when ct is grounded (timer disabled). 7 batt battery sense input. positive terminal of single li+ cell. 8 gnd ground 9 drv external transistor driver. this pin drives the gate/base of an external pmos/pnp pass transistor. 10 cs current-sense input. negative side of internal current-sense resistor. connect to source/emitter ofpmos/pnp pass transistor. downloaded from: http:///
max1898 linear charger for single-cell li+ battery _______________________________________________________________________________________ 7 led chg 0.1 f in 4.5v to 12v osc 2 18 ct charging for 3hr, c ct = 100nf rset (2.8k for 500ma charge current) iset timeout chg logic 5ma control logic 280mv iset (falling) 305mv iset (rising) ca va icharge < 20% ref 1.4v 1.4v1.4v restart hv drv prequal 2.5v done uvlo en/ok battin shutdown v l reg 3v 100k shutdown gnd shutdown done 69.275k 34.637k 2.653k rstrt 10 f batt drv cs 0.1 f 470 84m 84 20m dc in csa figure 1. functional diagram downloaded from: http:///
max1898 the iset pin is 1ma per amp of charging current. theoutput voltage at iset is proportional to charging cur- rent as follows: the voltage at iset is nominally 1.4v at the selected fast-charge current, and falls with charging current as the cell becomes fully charged. see figure 2 for typical li+ charging profile. chg status output chg is an open-drain output that monitors the cell s charging status. chg has a 5ma current limit so an led can be connected directly from in to chg for a visible indication. alternatively, a pullup resistor (typi-cally 100k ) to a logic supply provides a logic-level output. table 1 outlines the status of chg for various charger states. reinitiating a charging cycle the max1898 can be configured so that a chargingcycle automatically restarts when the cell voltage drops 200mv below the battery regulation voltage (connect rstrt to gnd). the restart threshold can also be low- ered by connecting an external resistor between rstrt and gnd. if automatic charging restart is not desired, this feature may be disabled by floating the rstrt pin. with restart disabled, charging can only be reinitiated by pulling en/ok low, or by removing and reapplying the input power source. en/ok (en input, ok output) the en/ok pin serves two functions. it primarily serves asa logic input (active high) to enable the charger. in addi- tion to on/off control, en/ok also indicates when input power is connected. when input power is applied to in (v in > v batt and v in > 4.25v) en/ok pulls high (to 3v) with a 100k internal pullup resistance. consequently, en/ok may be output to a logic input, to indicate acadapter presence, but at the same time may be driven by open-drain logic to turn the charger on and off. an open-drain logic-low input will over-ride the internal pullup resistor and turn off the charger (see figure 3). when the open drain goes high imped ance, en/ok will go high if v ir iset chg set = 1000 linear charger for single-cell li+ battery 8 _______________________________________________________________________________________ condition chg no battery or no charger input. high impedance (led off) the cell voltage is less than 2.5v and charge current is regulated to 10% of the selected fast-charge current (prequalification state). low impedance (led on) cell voltage is greater than 2.5v (fast-charge state). low impedance (led on) charge cycle complete charge current is less then 20% of the selected fast charge current or safety timer expires (3 hours for c ct = 100nf). high impedance (led off) charge cycle fault the cell voltage is less than 2.5v and the prequalification timer (45min for c ct = 100nf) has expired. blinking, led on 50% dutyfactor, 1.5hz table 1. chg output states off max1898 on power ok in gnd en/ok 3v 100k open-drain logic figure 3. driving en/ok with open-drain logic to retainon/off control with power ok indication 3.2 3.4 3.83.6 4.0 4.2 0 0.2 0.4 0.6 1.00.8 1.2 1.4 06 0 30 90 120 150 180 time (minutes) battery voltage (v) amps, watts, amp hours battery voltage amp hours battery current power dissipation figure 2. li+ charging profile downloaded from: http:///
power is present at in. if there is no (or insufficient)voltage at in, en/ok will remain low and the charger will remain off. battery drain current the max1898 uses advanced cmos circuitry to com-pletely monitor battery state, while drawing minimal current from the cell itself. when the input voltage is less than the battery, battery drain is typically 3?. when input power is present and charging is complete (the charge timer expires), battery drain is then typically 40?. this current may be reduced to 4? by disabling the restart feature. applications information the max1898 basic application circuit is shown infigure 4. an led can be added as a charge-state indicator. a 10? bypass capacitor must be added to the batt pin. a schottky diode should be added between the exter- nal transistor drain/collector and batt, to avoid battery discharge in the event of an input source short circuit. figure 5 shows a charger circuit using an external pnp pass transistor. selecting maximum charge time the maximum charge time can be set with an externalcapacitor connected from ct to gnd. select the timing capacitor using: where:t chg = nominal charge time limit in hours. the maximum charge timer is intended as a safety timer.it is normally not intended to be part of the charge-con- trol loop. when charging a li+ cell at a 1c rate, normal charge time is approximately 1.5 hours, but this may have wide variations that depend on temperature and cell type. in most cases, 3 hours is recommended for the maximum charge time limit when fast-charging at 1c so that normal-charging is never interrupted by the charge timer. consult the battery manufacturer for details on rec- ommended timer settings. the charge safety timer may also be completely dis- abled by connecting ct to ground. note: if the charge timer is disabled, both the restart function and prequali-fication fault indication are also disabled. only the indi- cation (blinking led) is disabled, the prequalification function itself is not modified. controlling automatic restart the max1898 features automatic restart that resumescharging when the cell voltage drops to a predetermined level. in most timed chargers, once charging times out, subsequent loading of the battery can discharge the bat- tery and charging will not resume unless the charger is restarted by an outside signal. by automatically resuming charging when the battery voltage drops, the max1898 ensures that the cell does not remain partially charged c nf t hours ct chg [] = [] 34 33. max1898 linear charger for single-cell li+ battery _______________________________________________________________________________________ 9 max1898 led cs drv batt gnd ct 6 3 2 1 iset in 4 8 5 7 9 10 en/ok rstrt chg 10 f 100nf li+ cell c ct , 100nf capacitor sets charge timeto 3hr output voltageproportional to charge current r set sets chargecurrent input power ok output or enable input charge indicator 5v to 12v figure 4. basic application circuit max1898 led cs drv batt gnd ct 6 3 2 1 iset in 4 8 5 7 9 10 en/ok rstrt chg 10 f 220nf li+ cell c ct , 100nf capacitor sets charge timeto 3hr output voltageproportional to charge current r set sets chargecurrent input power ok output or enable input charge indicator 5v to 12v figure 5. application circuit with pnp pass transistor downloaded from: http:///
max1898 after use when charger power is available. the restartfeature can be configured in the following ways: floating the rstrt pin disables restart. once thebattery is charged and the charge timer expires, charging can only be started by cycling input power to in, or by toggling en/ok. when the restart func- tion is disabled, battery drain after charge comple- tion is reduced to 4?. with the restart function enabled, battery drain current after charge comple- tion is 40?. ground the rstrt pin to enable the default restartthreshold of 4v for the max1898eub42 and 3.9v for the max1898eub41. once the battery is charged and the charge timer expires, charging restarts when the cell voltage drops to the restart-threshold voltage. if desired, lower the restart-threshold voltage by con-necting a resistor from rstrt to gnd. select the resistor using the following equations: for max1898eub42:for v rstrt values between 3v and 4v. for max1898eub41: for v rstrt values between 3v and 3.9v. note that if ct is grounded (charge timer disabled), therestart function is also disabled. rk k v v k rstrt rstrt [] = ? ?? ?? ? ? ?? ?? ? ? ? 66 822 14 1 37 301 . . . rk k v v k rstrt rstrt [] = ? ?? ?? ? ? ?? ?? ? ? ? 69 275 14 1 37 301 . . . linear charger for single-cell li+ battery 10 ______________________________________________________________________________________ v batt < 2.5v timeout/4expires and v batt < 2.5v rstrt = gnd andv batt < 4.0v (max1898eub42) v batt < 3.9v (max1898eub41) prequalification 10% charge current led = on fast charge 100% charger current led = on top off led = off shutdown charger = off led = off fault led blinking at 1.5hz done (charge complete) charger = off led = off asynchronous from anywhere v in < 4.5v or v batt > v in v in < 4.5v or v batt > v in v batt > 2.5v, 3hr timer starts timeout = 3hr icharge < 20%of iset dotted line indicates the states that are not available when ct = 0 (timer disabled) icharge > 22% of iset timeout = 3hr figure 6. charger state diagram external transistors resistance rating voltage limit (v) power dissipation (w) package comments pmosfairchild ndt454p 50m -30 3 sot223 pnpzetex fzt968 0.17v, v ce(sat) -15 3 sot223 h fe = 300min pnpfcx717 0.32v, v ce(sat) -12 1 sot89 h fe = 160min, 1w rating suitable for0.5a charge or less table 2. external transistors downloaded from: http:///
selecting external components the max1898 drives an external transistor to controlcharging current. the most important specifications for the pass transistor (mosfet or bipolar) are current rating and package power dissipation. since the max1898 operates as a linear charger, heat will dissipate in the external tran- sistor. the worst-case power dissipation will be: p diss(max) = i fastchg (v in - 2.5v) the pass transistor and heatsinking (typically an expand-ed pc board plane) must be rated for p diss(max) . the pass device will most commonly be a p-channelmosfet. its operating voltage must exceed the expected input voltage, but mosfet on-resistance is important only in low-dropout designs where v in is only slightly higher than the battery regulation voltage. inmost charger designs, a fairly low-cost fet (around 100m to 200m r ds(on) ) performs more than ade- quately. lower resistance fets perform well also, butare not worth the added cost in this case. a pnp bipolar transistor may also be used as a passdevice. drv can sink up to 4ma, so reasonable high current gain (h fe or beta) is required to allow drv to drive the base of a bipolar pass transistor. for a 500mafast-charge current, an h fe of 125 is required. although their current gain is high, darlington pnp transistors arenot recommended due to stability limitations. if v in is less than v batt , the body diode inherent in the external enhancement-mode fet allows current to flowfrom the cell back to the source. to prevent this, add a schottky diode between the drain and batt, as shown in figure 4. chip information transistor count: 1816process: bicmos max1898 linear charger for single-cell li+ battery ______________________________________________________________________________________ 11 downloaded from: http:///
max1898 linear charger for single-cell li+ battery 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. 12 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2002 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information 10lumax.eps downloaded from: http:///

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