BQ2902 Datasheet, PDF (4/12 Pages) Texas Instruments – Rechargeable Alkaline Charge/Discharge Controller IC

bq2902
tial of any battery is above the maximum open-circuit
voltage (VMAX = 1.63V ±3%), the following pulses are
skipped until all cell potentials fall below the VMAX
limit. Charging is terminated when the average charge
rate falls below approximately 3% of the maximum
charge rate. Once charging is terminated, the internal
charging FET remains off, and the CHG output becomes
active per Table 1 and Figure 2. With DC applied, the
internal discharge FET will always remain on.
discharge voltage (VEDV) is selectable by connecting the
VSEL pin as outlined in Table 2. Typically, higher dis-
charge loads (>200mA) should use a lower discharge
voltage cut-off to maximize battery capacity.
End-of-Discharge Control
When DC is not present or less than the voltage present
on the BAT1P pin, the bq2902 power is supplied by the
voltage present at the BAT1P pin. In this state, the bat-
teries discharge down to the level determined by the
VSEL pin. The bq2902 monitors the cell voltage of the re-
chargeable alkaline cells.
If the voltage across any cell is below the voltage speci-
fied by the VSEL input, the bq2902 disconnects the bat-
tery stack from the load by turning the internal
discharge FET off. The discharge FET remains off until
either the batteries are replaced or DC is reapplied, ini-
tiating a new charge cycle. After disconnecting the bat-
tery stack from the load, the standby current in the
bq2902 is reduced to less than 1µA. The end-of-
Table 2. bq2902 EDV Selections
End-of-Discharge Voltage
1.10V
1.00V
0.90V
Pin Connection
VSEL = BAT1P
VSEL = Z
VSEL = VSS
BAT1P
CHG
DC Valid
Pending
12.5ms
2/3 sec. 1/6 sec.
Charging 1
10ms
2
Charge
Complete
3
Notes: 1. Charging: 0.4 < VOCV < 1.63V, VCCV < 3.0V.
2. Pulses skipped when VOCV > 1.63V.
3. Charge complete when average charge falls below 3% of fast charge rate
TD290201.eps
Figure 2. bq2902 Application Diagram
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