1 of 4 introduction the ds2714 evaluation kit (ev kit) displays all features of the ds2714 nimh charger. the board is set up to be used with an external current source as the charge supp ly. the fast-charge timeout is set for 2.5hrs. dmsel is floating, and v ctst is set to approximately 296mv. connections gnd should be connected to a common ground between vd d and vchg. vdd supplies power to the ds2714 and leds. vchg supplies the current for charging the cells. vdd and vchg must be separate supplies. the loading of vchg causes the voltage to drop out, resulting in a re set of the ds2714 if one supply is used to power both the ds2714 and vchg. ordering information part type DS2714EVKIT+ ev kit + denotes lead(pb)-free and rohs compliant. evaluation board schematic DS2714EVKIT+ quad loose-cell nimh charge r evaluation kit www.maxim-ic.com 19-4839; rev 8/09 downloaded from: http:///
DS2714EVKIT+ 2 of 4 supply connection diagram ds2714 evaluation board fast charge time and top-off time adjustment fast charge and top-off time are controlled by the exter nal resistor r21. resistor s can be selected to support fast charge timeout periods of 0.5hr s to 10hrs. top-off charge timeout is one-half of fast charge timeout. the programmed charge time approximately follows the equation: t = 1.5 x r/1000 (time in minutes) the evaluation board value of r21 is 100k ? giving a fast charge timeout of 150 minutes, 2.5hrs. cell test voltage adjustment v ctst is controlled by the external resist or r20. resistors can be selected to support ctst values from 32mv to 400mv. the programmed ctst value approximately follows the equation: v ctst = 8000/r (value in volts) the evaluation board value of r20 is 27k ? giving ctst a value of approximately 296mv. downloaded from: http:///
DS2714EVKIT+ 3 of 4 cell test vo ltage value ctst values should be select ed based on cell imped ance and charge rate. you will w ant to select a ctst value that will allow the ds2714 to reject an alkaline cell but charge an empty nimh. the following formula shows the relationship between charge rate, ctst, and cell impedance: v ctst = (charge rate) x (cell impedance) using a charge rate of 2a assuming a cell impedance of 52m ? will give you a v ctst = 104mv. this can be a delicate selection process because some aged nimh cells can have an impedance greater than new alkaline cells. the following table shows the impedance value of a few typical cells. charge states impedance (m ? ? cell type cell brand full low empty depleted duracell ultra 181 451 910 671 rayovac maximum plus 248 761 1282 462 energizer max 140 912 1080 524 energizer e 2 lithium 159 174 272 850 alkaline - aa energizer e 2 titanium 186 436 486 444 panasonic (1950mahr) 42 52 60 448 rayovac (2000mahr) 40 48 64 638 new nimh - aa sanyo (1600mahr) 34 54 206 982 maxell (2000mahr) 58 285 555 629 rayovac (1800mahr) 45 55 187 391 sanyo (2000mahr) 81 83 131 812 aged nimh - aa sony (2000mahr) 57 116 551 1420 led blink rates led blink rates are controlled by the dmsel pin. dmsel is floating and can be shorted to vdd or gnd through resistor connection pads r6 and r7, respectively. charge activity display mode dmsel pin no battery pre/fast/top-off charging maintenance fault dm0 low high-z low 0.75s low 0.25s high-z 0.5s low 0.5s high-z dm1 float high-z low high-z 0.125s low 0.125 high-z dm2 high high-z 0.75s low 0.25s high-z low 0.125s low 0.125s high-z downloaded from: http:///
DS2714EVKIT+ 4 of 4 maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the ci rcuitry and specifications wi thout notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2009 maxim integrated products maxim is a registered tra demark of maxim integrated products. revision history revision date description pages changed 8/09 changed the ordering part number from ds2714k to DS2714EVKIT+. all downloaded from: http:///
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