BAT+

bq2000T

2

4

BAT

VSS

RB1

RB2

bq2000T

SLUS149D – MAY 1999 – REVISED JANUARY 2010

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Initiation and Charge Qualification

The bq2000T initiates a charge cycle when it detects

•

Application of power to VCC

•

Battery replacement

•

Exit from sleep mode

•

Capacity depletion (Li-Ion only)

Immediately following initiation, the IC enters a charge-qualification mode. The bq2000T charge qualification is

based on battery voltage and temperature. If the voltage on the BAT pin is less than the internal threshold, VLBAT,

the bq2000T 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 bq2000T 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 pulse-width is user-selectable and is set by the value of the resistance connected between the RC pin and

VSS.

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

Once battery conditioning (trickle charge) has raised the voltage on the BAT pin above VLBAT, the IC enters fast

charge, if the battery temperature is within the VLTF to VHTF range. The bq2000T stays in the battery conditioning

state indefinitely and does not progress to fast charge until the voltage on the BAT pin is above VLBAT and the

temperature is within the VLTF and VHTF range. No timer is implemented during battery conditioning.

Battery Chemistry

The bq2000T detects the battery chemistry by monitoring the battery-voltage profile during the initial stage of the

fast charge. If the voltage on the BAT pin rises to the internal VMCV reference, the IC assumes a Li-Ion battery.

Otherwise, the bq2000T assumes a NiCd/NiMH chemistry. While in the fast charge state, the LED pin is pulled

low (the LED is on).

As shown in Figure 3, a resistor voltage-divider between the battery pack's positive terminal and VSS scales the

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 bq2000T 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 bq2000T 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 maintenance-charge that continues as long as the voltage on the BAT pin remains below VMCV.

6

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