DS2715 查看數據表（PDF） - Maxim Integrated

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DS2715

NiMH Battery Pack Charge Controller

Maxim Integrated 

DS2715: NiMH Battery Pack Charge Controller

Application Circuits

Switchmode

Figure 5 shows a typical DS2715 switchmode application circuit for charging a 3-cell battery stack. Connecting the

MODE pin to CBIAS enables the comparator mode of current regulation. The DS2715 regulates the current

through the current sense resistor R7 by switching Q1 on and off as the sense resistor voltage ramps up and down

toward the preset sense voltage thresholds. The .1ohm sense resistor along with the DC ground-referenced sense

threshold level of -(VFC + VHYS-FC/2) sets the average charge current in the example to 1.07A. The sense resistor

should have a proper power rating for the chosen charge current.

Figure 5. TYPICAL Switchmode APPLICATION CIRCUIT FOR A 3-CELL

STACK

A bootstrap subcircuit with C5, R3 and Q3 is used to improve the turnoff time of Q1 to minimize switching losses.

When VCH is pulled low to turn on Q1, C5 is charged through the R6/R3 path. When VCH is left open-circuit to turn

off Q1, the voltage of the VCH node jumps up close to the gate voltage of Q1. This causes the gate of Q3 to be

pushed up due to the voltage across C5. Q3 is then turned on, which helps to speed turn-off of Q1 by discharging

its internal capacitances. The values of the components in this section of the circuit are tuned to work with the

chosen transistors. The values of R6 and R9 should be chosen so that no more than 20mA is sunk by VCH. D4 is

used to clamp the inductive spike that could occur if the batteries are removed during charging. This function can

also be served by an energy absorbing capacitor placed in parallel with the battery stack.

Q2 is used to float the Rt pin when the supply source is disconnected. This puts the DS2715 into SUSPEND mode

and resets the state machine. D1 prevents current from flowing into the charge source. D2 and R2 create the

maintenance charge current path. D1, D2 and R2 should be sized appropriately for the wattage they must dissipate

based on the application parameters. R1 and C3 create a low pass filter to minimize noise transfer as the DS2715

local ground moves in relation to the system or charge source ground.

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