DS2715 データシートの表示（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS2715

NiMH Battery Pack Charge Controller

Dallas Semiconductor -> Maxim Integrated 

DS2715: NiMH Cell Pack Charge Controller

DONE state. If at any time during fast charge the voltage on VBATT exceeds 1.65V (VOPEN), the DS2715 determines

that the cell pack has been removed and returns to the PRESENCE state.

Top-Off

In top-off mode, the DS2715 regulates the voltage across the sense resistor to -33mV (VTO) in linear mode or -

29mV (VTO - 0.5 x VHYS-TO) in comparator mode. LED1 indicates the cell pack is being charged. The charge timer is

reset and restarted with a time-out period of one half the fast-charge duration. When the charge timer expires or if

the measured temperature exceeds 50°C, the charger enters the DONE state.

DONE/Maintenance

The DS2715 enters the DONE state whenever the charge completes normally or if the measured cell temperature

exceeds 50°C during the charge. While in the done state VCH is driven to high impedance to prevent further

charging of the cell pack and LED is driven on to indicate charge completion. A maintenance charge can be

applied to the cells by providing a resistive path from the cell pack to the charge source bypassing the regulator.

See the example circuit in Figure 3. The DS2715 remains in DONE until a cell voltage greater than 1.65V (VOPEN) is

detected on VBATT indicating the cell pack has been removed. The DS2715 then enters the PRESENCE state and

waits for the next cell insertion.

FAULT

The DS2715 enters FAULT if pre-charge is unable to charge the cell above 1.0V (VLB) before the 30 minute pre-

charge timeout of if the cell temperature exceeds 50°C during pre-charge. In the fault state VCH is driven to high

impedance and LED2 blinks to indicate the fault condition. The DS2715 remains in FAULT until a cell voltage

greater than 1.65V (VOPEN) is detected on VBATT indicating the cell pack has been removed. The DS2715 then

enters the PRESENCE state and waits for the next cell insertion.

Discharge Mode

When the DS2715 detects a discharge current voltage drop of VDCHG-SET or greater across the sense resistor,

charging is terminated and the DS2715 enters the DISCHARGE state. While in this mode, voltage sensing, thermal

sensing, and LED outputs are disabled. The VCH pin is driven low to allow the pack to be discharged. Current drain

of the DS2715 drops to IDDD. The DS2715 remains in discharge mode until a charge current of at least VDCHG-RST is

detected. When this occurs the DS2715 enters the presence detect state to begin a new charge cycle.

Application Circuit

Figure 3 shows a typical application circuit for charging a 3-cell stack. The mode pin is tied to VSS for linear

operation. A 75mΩ sense resistor (R10) sets the charge current at 1.6A. The DS2715 regulates the current through

Q1. 68kΩ on RT (R6) sets the fast charge timeout to 102 minutes. R5 and R8 form a 1:3 voltage divider to allow

VBATT to measure the voltage of a single cell. The charge source is isolated with diode CR1 to prevent discharge

through the source connection. R1 and CR2 form a maintenance charge path to supply the cell pack with ~40mA

constant current after the charge completes. Lastly VR1 and R4 create a current leakage path to bias the regulator

circuit and prevent an in-rush current spike when the cell stack is connected to the powered circuit.

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