BAT+

bq2000

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4

BAT

bq2000

SLUS138D – JANUARY 2008 – REVISED DECEMBER 2009

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Initiation and Charge Qualification

The bq2000 initiates a charge cycle when it detects

•

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Battery replacement

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Exit from sleep mode

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Capacity depletion (Li-Ion only)

Immediately following initiation, the IC enters a charge-qualification mode. The bq2000 charge qualification is

the bq2000 enters the battery conditioning state. This condition indicates the possibility of a defective or shorted

battery pack. In an attempt to revive a fully depleted pack, the bq2000 enables the MOD pin to trickle-charge at a

rate of once every 1.0s. As explained in the section "Top-Off and Pulse-Trickle Maintenance Charge," the trickle

During charge qualification, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger.

Battery Chemistry

The bq2000 detects the battery chemistry by monitoring the battery-voltage profile during the initial stage of the

Otherwise, the bq2000 assumes a NiCd/NiMH chemistry. While in the fast charge state, the LED pin is pulled low

(the LED is on).

battery voltage. A low-pass filter then smooths out this voltage to present a clean signal to the BAT pin. In a

mixed-chemistry design, a common voltage-divider is used as long as the maximum charge voltage of the

nickel-based pack is below that of the Li-Ion pack. Otherwise, different scaling is required.

Figure 3. Battery Voltage Divider and Filter

Once the chemistry is determined, the bq2000 completes the fast charge with the appropriate charge algorithm

(Table 1). The user can customize the algorithm by programming the device using an external resistor and a

capacitor connected to the RC pin, as discussed in later sections.

NiCd and NiMH Batteries

Following charge qualification (which includes trickle charge, if required ), the bq2000 fast-charges NiCd or NiMH

batteries using a current-limited algorithm. During the fast-charge period, it monitors charge time, temperature,

and voltage for adherence to the termination criteria. This monitoring is further explained in later sections.

Following fast charge, the battery is topped off, if top-off is selected. The charging cycle ends with a trickle

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