Trickle

Time

Phase1

Phase2

FastCharge

Voltage

Current

bq2000

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SLUS138D – JANUARY 2008 – REVISED DECEMBER 2009

Lithium-Ion Batteries

The bq2000 uses a two-phase fast-charge algorithm for Li-Ion batteries (Figure 4). In phase one, the bq2000

and changes the termination method from PVD to minimum current. The bq2000 then moves to phase two,

threshold or the timer expires (whichever happens first). A new charge cycle is started if the cell voltage falls

Figure 4. Lithium-Ion Charge Algorithm

During the current-regulation phase, the bq2000 monitors charge time, battery temperature, and battery voltage

for adherence to the termination criteria. During the final constant-voltage stage, in addition to the charge time

and temperature, it monitors the charge current as a termination criterion. There is no post-charge maintenance

mode for Li-Ion batteries.

Table 1 summarizes the charging process for both Nickel and Li-Ion batteries.

Table 1. Charge Algorithm

BATTERY CHEMISTRY

CHARGE ALGORITHM

1. Charge qualification

2. Trickle charge, if required

3. Fast charge (constant current)

NiCd or NiMH

4. Charge termination (peak voltage, maximum charge time = 1 MTO)

5. Top-off (optional)

6. Trickle charge

1. Charge qualification

2. Trickle charge, if required

Li-Ion

3. Fast charge (constant current)

4. Fast charge (constant voltage)

5. Charge termination (minimum current, maximum charge time = 2 MTO)

FAST CHARGE TERMINATION

Initial Hold-OFF Period

The bq2000 incorporates a user programmable hold-off period to avoid premature fast charge termination that

can occur with brand new cells at the very beginning of fast charge. The values of the external resistor and

capacitor connected to the RC pin set the initial hold-off period. During this period, the bq2000 avoids early

termination due to an initial peak in the battery voltage by disabling the peak voltage-detection (PVD) feature.

This period is fixed at the programmed value of the maximum charge time (MTO) divided by 32.

Copyright © 2008–2009, Texas Instruments Incorporated

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