DS2715 datasheet(7/17 Pages) MAXIM

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DS2715: NiMH Battery Pack Charge Controller

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DETAILED DESCRIPTION

Charge Cycle Overview

The DS2715 regulates the charge of up to 10 NiMH cells in a series configuration. With the mode select pin, the

DS2715 can be configured to regulate either as an error amplifier in linear mode or as a comparator in switched

mode. A charge cycle begins in one of two ways: with the application of power to the DS2715 while the cell pack is

already inserted, or with the detection of cell insertion after power-up.

After cell presence confirmation, PRECHARGE qualification occurs to prevent fast charging of deeply depleted

cells or charging under extreme temperature conditions. Pre-charging is performed at a reduced rate of

approximately ¼ the FAST-CHARGE current until each cell reaches 1V. The algorithm then proceeds to the FAST-

CHARGE phase. Fast charging continues as long as the cell pack temperature is less than 50

C based on the

THM voltage, and the cell voltage as measured at the VBATT pin in the middle of the resistor divider remains below

1.65V, indicating the cell pack is still present. Fast charging terminates normally by measuring the cell pack’s

thermal rate of change, dT/dt. When the cell pack’s thermal rate of change exceeds 0.5°C per minute, the DS2715

enters TOPOFF. The DS2715 has an internal charge timer as secondary overcharge protection if the charge is not

terminated properly by the dT/dt method. The charge termination timer duration is user selectable from 30 minutes

up to 6 hours by an external resistor on the RT pin.

Following a normally terminated or timed-out FAST-CHARGE phase, the DS2715 enters TOPOFF. It remains in

this state for one-half (one-quarter for DS2715B) of the period of the FAST-CHARGE timeout as selected by the

external resistor on RT. After the TOPOFF charge timer expires, the DONE phase continues indefinitely until the

cell pack is removed from the charger or DISCHARGE mode is entered. For the standard application circuit

configuration, when a load drawing at least Vdchg-set across the sense resistor is attached to the cell pack, the

DS2715 switches to DISCHARGE mode. All charge functions are disabled and the regulation FET is driven on to

allow the cell pack to discharge. Throughout the charging process, the open-drain LED1 output indicates the

charge status to the user.

Undervoltage Lockout (Reset)

The UVLO circuit serves as a power-up and brownout detector by monitoring VDD to prevent charging until VDD

rises above VUVLO, or when VDD drops below VUVLO - VUVLO-HYS. If UVLO is active, charging is prevented, the state

machine is forced to the RESET state, and all charge timers are reset. A 10

s deglitch circuit provides noise

immunity. Once VDD reaches an acceptable operating voltage, the DS2715 enters the PRESENCE state.

DS2715 データシート(PDF) 7 Page - Maxim Integrated Products