BQ2002D_14 Datasheet, PDF (6/17 Pages) Texas Instruments – NiCd/NiMH Fast-Charge Management ICs

bq2002D/T
enforced again on the top-off phase, if selected (bq2002T
only). There is no time limit on the trickle-charge
phase.
Top-off Charge—bq2002T Only
An optional top-off charge phase may be selected to
follow fast charge termination for 1C and C/4 rates.
This phase may be necessary on NiMH or other bat-
tery chemistries that have a tendency to terminate
charge prior to reaching full capacity. With top-off en-
abled, charging continues at a reduced rate after
fast-charge termination for a period of time selected
by the TM pin. (See Table 1.) During top-off, the CC
pin is modulated at a duty cycle of 286µs active for
every 4290µs inactive. This modulation results in an
average rate 1/16th that of the fast charge rate. Maxi-
mum voltage, time, and temperature are the only ter-
mination methods enabled during top-off.
Pulse-Trickle Charge—bq2002T Only
Pulse-trickle is used to compensate for self-discharge
while the battery is idle in the charger. The battery is
pulse-trickle charged by driving the CC pin active for a
period of 286µs for every 72.9ms of inactivity for 1C and
2C selections, and 286µs for every 17.9ms of inactivity
for C/4 selection. This results in a trickle rate of C/256
for the top-off enabled mode and C/128 otherwise.
TM Pin
The TM pin is a three-level pin used to select the
charge timer, top-off, voltage termination mode,
trickle rate, and voltage hold-off period options. Table
1 describes the states selected by the TM pin. The
mid-level selection input is developed by a resistor
divider between VCC and ground that fixes the voltage
on TM at VCC/2 ± 0.5V. See Figure 5.
Charge Status Indication
In the fast charge and charge pending states, and when-
ever the inhibit pin is active, the LED pin goes low. The
LED pin is driven to the high-Z state for all other condi-
tions. Figure 3 outlines the state of the LED pin during
charge.
Charge Inhibit
Fast charge and top-off may be inhibited by using the
INH pin. When high, INH suspends all fast charge and
top-off activity and the internal charge timer. INH
freezes the current state of LED until inhibit is re-
moved. Temperature monitoring is not affected by the
INH pin. During charge inhibit, the bq2002D/T contin-
ues to pulse-trickle charge the battery per the TM selec-
tion. When INH returns low, charge control and the
charge timer resume from the point where INH became
active. The VTS sample history is cleared by INH.
Low-Power Mode
The IC enters a low-power state when VBAT is driven
above the power-down threshold (VPD) where
VPD = VCC - (1V ±0.5V)
Both the CC pin and the LED pin are driven to the
high-Z state. The operating current is reduced to less
than 1µA in this mode. When VBAT returns to a value
below VPD, the IC pulse-trickle charges until the next
new charge cycle begins.
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