general description the ds2731 evaluation kit (ev kit) demonstrates all thefeatures of the ds2731 battery-backup power-man- agement ic. the ev kit includes an assembled and tested pcb for easy connection to power sources and a load. three power sources? 3.3v auxiliary supply, a 12v supply, and a single lithium-ion (li+) battery connect to the ds2731 ev kit to supply the high-effi- ciency, synchronous buck regulator and battery charger. the ic automatically selects the best-quali- fied power source for the buck regulator. thresholds for low-battery voltage, charge regulation voltage and current, charge safety timer, and buck-output voltage are set by resistors. features ? convenient power source and load connections ? leds indicate charge status ? automatic power-source selection ? space for a wide variety of inductor sizes ? proven, compact and low-cost pcb layout ? fully assembled evaluates: ds2731 ds2731 evaluation kit ________________________________________________________________ maxim integrated products 1 19-4842; rev 1; 10/09 component list for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information designation qt description c1, c7 2 10f ceramic smt capacitors c2, c3, c6 3 47f ceramic smt capacitors c4, c5 2 22f ceramic smt capacitors g 1 green led l62305ct jp1 1 no power jp2 1 0 resistor (0603) l1 1 2.2h power inductor l2 1 6.8h power inductor r 1 red led l62301ct r1 1 56.2k resistor (0603) r2 1 10.2k resistor (0603) r3 1 590k resistor (0603) designation qt description r4 1 240k resistor (0603) r5 1 360k resistor (0603) r6, r7, r8, r11, r12 5 4.7k resistor (0603) r9 1 0.05k resistor (1206) r13 1 2.49k resistor (0603) thm1 1 103at-2 thermistor u1 1 cache-memory battery-backup management ic (28 tssop) ds2731e+ y 1 yellow led l62307ct 1 pcb: ds2731 evaluation kit+ part tpe DS2731EVKIT+ ev kit + denotes lead(pb)-free and rohs compliant. downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit 2 _______________________________________________________________________________________ 12v 3.3v load figure 1. quick start connection diagram quick start sequence required equipment before beginning, the following equipment is needed: ds2731 ev kit board +12v power supply +3.3v power supply +4.2v li+ battery voltmeter connecting wires optional equipment the following equipment is recommended but notrequired: programmable load (150ma at +1.7v typical) source/sink power supply board connections 1) connect a +4.2v source/sink supply or a li+ bat- tery between bat+ and bat-. 2) connect a +12v supply between vin and cgnd. 3) connect a +3.3v supply between aux and cgnd. 4) connect a load between mem+ and mem- (option- ally connect a voltage meter). 5) verify the regulator output at mem+/mem-, which should be close to +1.8v with no load. caution: always observe proper esd precautionswhen handling the ds2731 ev kit circuit board. supply connections a valid +12v and +3.3v supply are required for thecharger circuitry to function. the charge current is drawn directly from the +12v supply. the majority of the device logic and the buck regulator are powered off the +3.3v auxiliary supply. these supplies share a common ground at cgnd. battery connection connect a +4.2v li+ cell between bat+ and bat-. asource/sink supply can be used for board evaluation purposes. downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit _______________________________________________________________________________________ 3 i i charge chargebegin precharge mode constant-current mode constant-voltage mode charge end v i 10% x i charge vt v pk v min charge termination 5% x i charge figure 2. li+ charge cycle board configuration charger/buck regulator enables ( ens , enc) the charger circuitry can be disabled by removing the0 resistor on jp2. the board is shipped with the 0 resistor in place (charger enabled).similarly, the buck regulator can be disabled by pulling ens high through a 0 resistor on jp1. the board is shipped without the 0 resistor in place (buck regulator enabled). setting charge parameters constant current (cc) current is regulated based on the voltage drop acrossan external 50m sense resistor and an internal feed- back circuit. the cc charge rate, i charge , is set at the rset pin. it can be calculated by the following formula: i charge = 2500/r where r is the value of the resistor connected to rset.the charge current can range from 0.5a to 1.5a. the board is shipped with i charge = 1.00a. constant voltage (cv) when the battery voltage reaches the cv output thresh-old, cv mode is entered. the charger stops regulating current and begins regulating voltage. the margin pin sets the cv threshold according to the following formula: v pk (cv set point) = 4.97v x r1/(r2 + r1) where r2 is the resistor between stmr and margin,and r1 is the resistor between margin and ground. voltage regulation can be set from +3.8v to +4.6v. the board is shipped with v pk = +4.21v. smtr the charger has a safety timer that sets the maximumlength of time for a charge cycle. it is programmable from 1hr to 10hr. timing equation: 0.1647 x r stmr = t(s); r stmr = r1 + r2 the board is shipped with t = 10,936s = 3.04hr. if thistimer expires and the battery fails to reach the termina- tion current, the charger enters the fault state and is latched off. charging does not continue until either the downloaded from: http:///
evaluates: ds2731 power is cycled or the enc pin is strobed low and thenreturns high. the timer does not start until cc mode is entered and continues through cv mode; precharge mode is not included in the stmr. buck regulator regulation voltage the buck regulator output voltage can range from+0.9v to +2.5v and is set by the following formula: v div x 25/12 = v vreg the board is shipped with v reg = +1.8v. low-battery shutdown the supply powering the buck regulator is the auxiliarysupply as long as it is > 2.93v. if the voltage of the aux- iliary supply drops below 2.93v, the ds2731 automati- cally switches power to the li+ battery. the ic transitions to a quiescent-power mode should the li+ battery reach empty before the system power is restored. in this mode, all circuitry is shut off and does not turn on again until the v cbias voltage is stable and uvlo-reg is off. the low-battery voltage set point canbe determined by the following formula: v lo_batt x 4.5 = low-battery voltage set point the board is shipped with the low-battery voltage setpoint = +2.76v. board operation charger the features of the charge circuitry can be easilydemonstrated when a source/sink supply is connected between bat+ and bat-. with the +12v and +3.3v supplies connected and on, lower the source/sink sup- ply? voltage below +4.0v (make sure the current limit of the supply is set above the charge current i charge ). the yellow led should turn on. if the source/sink sup-ply has a current meter display, it should read approxi- mately equal to i charge . lower the source/sink supply voltage below v min and there is a reduction in the charge current. increase the source/sink supply volt-age above v pk , the constant voltage set point, and observe the green led turn on.heat the ic up to > +160?. above +100?, the ic begins to choke the charge current 133ma/?. once the die temperature exceeds +160?, the charge cur- rent shuts off completely. buck regulator with the +12v and +3.3v supplies and the li+ batteryconnected, the voltage reading between mem+ and mem- should be approximately +1.8v. if a programma- ble load is being used, set the load current to 150ma. the user should be able to observe the current being drawn from the +3.3v auxiliary supply. power down the +12v and +3.3v supplies and observe that the buck regulator is still running. power up the +12v and +3.3v supplies again and operation of the buck regulator should remain constant during the switchovers. ds2731 evaluation kit 4 _______________________________________________________________________________________ downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit _______________________________________________________________________________________ 5 22 chg1 21 l2 6.8 h chg2 25 sns 10 agnd 3 ctg c1 10 f r9 0.05 r5 360k r4 240k r3 590k 18 y charge r8 4.7k 17 r fault r7 4.7k 16 g done r6 4.7k 23 vin 24 cgate thm110k or 103at-2 c7 10 f c5 22 f c4 22 f c647 f 4 aux 15 enc 14 ens 5 cbias 12 lo_batt 13 div 11 ref r2 10.2k r13 2.49k r1 56.2k 1 margin 2 stmr 27 rset 20 cgnd1 19 cgnd2 28 thm 26 batt+ isolated ground area isolated ground area 6 vreg 8 l1 2.2 h lx 7 cin 9 sgnd c247 f c347 f r12 4.7k r11 4.7 jp2 0 jp1 np ds2731 u1 j3 vin 1 j1 battery+ 1 j2 battery- j9 test 1 j8 mem+ 1 j10 mem- 1 1 j5 aux+ 1 j6 enc j7 ens 1 1 j4 cgnd 1 figure 3. ds2731 ev kit board schematic downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit 6 _______________________________________________________________________________________ figure 4. ds2731 ev kit board?op view downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit _______________________________________________________________________________________ 7 figure 5. ds2731 ev kit board?iddle layer downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit 8 _______________________________________________________________________________________ figure 6. ds2731 ev kit board?ottom layer downloaded from: http:///
evaluates: ds2731 ds2731 evaluation kit revision history revision number revision date description pages changed 0 1/09 initial release. 1 10/09 changed the part number in the ordering informaio n table from ds2731k to DS2731EVKIT+. 1 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 _____________________ 9 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. downloaded from: http:///
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