BQ2000_15 Datasheet, PDF (7/29 Pages) Texas Instruments – Programmable Multi-Chemistry Fast-Charge Management IC

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
regulates constant current until V_BAT rises to V_MCV. Once V_BAT = V_MCV, the device identifies the cell as a Li-ion,
and changes the termination method from PVD to minimum current. The bq2000 then moves to phase two,
regulates the battery with constant voltage of V_MCV, and terminates when the charging current falls below the I_MIN
threshold or the timer expires (whichever happens first). A new charge cycle is started if the cell voltage falls
below the V_RCH threshold.
I_MAX
Voltage
V_MCV
Trickle
I_MIN
Fast Charge
Phase 1
Phase 2
Current
V_LBAT
Time
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.
BATTERY CHEMISTRY
NiCd or NiMH
(V_BAT < V_MCV always)
Li-Ion
(V_BAT ≤ V_MCV )
Table 1. Charge Algorithm
CHARGE ALGORITHM
1. Charge qualification
2. Trickle charge, if required
3. Fast charge (constant current)
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
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.
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