IMAX

IMIN

Trickle

VLBAT

VMCV

Time

Phase1

Phase2

FastCharge

Voltage

Current

bq2000T

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SLUS149D – MAY 1999 – REVISED JANUARY 2010

Lithium-Ion Batteries

The bq2000T uses a two-phase fast-charge algorithm for Li-Ion batteries (Figure 4). In phase one, the bq2000T

regulates constant current until VBAT rises to VMCV. Once VBAT = VMCV, the device identifies the cell as a Li-ion,

and changes the termination method from

ΔT/Δt to minimum current. The bq2000T then moves to phase two,

regulates the battery with constant voltage of VMCV, and terminates when the charging current falls below the IMIN

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

below the VRCH threshold.

Figure 4. Lithium-Ion Charge Algorithm

During the current-regulation phase, the bq2000T 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

(VBAT < VMCV always)

4. Fast charge termination (rate of temperature rise, 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)

(VBAT ≤ VMCV )

4. Fast charge (constant voltage)

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

Copyright © 1999–2010, Texas Instruments Incorporated

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