BQ2002FSNTRG4 Datasheet, PDF (5/17 Pages) Texas Instruments – NiCd/NiMH Fast-Charge Management ICs

bq2002/F
PVD and -∆V Termination
There are two modes for voltage termination depending
on the state of TM. For -∆V (TM = high), if VBAT is
lower than any previously measured value by 12mV
±3mV, fast charge is terminated. For PVD (TM = low or
mid), a decrease of 2.5mV ±2.5mV terminates fast
charge. The PVD and -∆V tests are valid in the range
1V < VBAT < 2V.
Voltage Sampling
Voltage is sampled at the BAT pin for PVD and -∆V ter-
mination once every 17s. The sample is an average of
voltage measurements taken 570µs apart.The IC takes
32 measurements in PVD mode and 16 measurements
in -∆V mode. The resulting sample periods (9.17 and
18.18ms, respectively) filter out harmonics centered
around 55 and 109Hz. This technique minimizes the ef-
fect of any AC line ripple that may feed through the
power supply from either 50 or 60Hz AC sources. Toler-
ance on all timing is ±20%.
Voltage Termination Hold-off
A hold-off period occurs at the start of fast charging.
During the hold-off time, the PVD and -∆V terminations
are disabled. This avoids premature termination on the
voltage spikes sometimes produced by older batteries
when fast-charge current is first applied. Maximum
voltage and temperature terminations are not affected
by the hold-off period.
Maximum Voltage, Temperature, and Time
Any time the voltage on the BAT pin exceeds the maxi-
mum cell voltage,VMCV, fast charge or optional top-off
charge is terminated.
Maximum temperature termination occurs anytime the
voltage on the TS pin falls below the temperature cut-off
threshold VTCO.
Maximum charge time is configured using the TM pin.
Time settings are available for corresponding charge
rates of C/2, 1C, and 2C. Maximum time-out termina-
tion is enforced on the fast-charge phase, then reset, and
enforced again on the top-off phase, if selected. There is
no time limit on the trickle-charge phase.
Top-off Charge
An optional top-off charge phase may be selected to
follow fast charge termination for 1C and C/2 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
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 18.0ms of inactivity for 1C and
2C selections, and 286µs for every 8.86ms of inactivity
for C/2 selection. This results in a trickle rate of C/64
for the top-off enabled mode and C/32 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 de-
scribes the states selected by the TM pin. The mid-
level selection input is developed by a resistor di-
vider between VCC and ground that fixes the voltage
on TM at VCC/2 ± 0.5V. See Figure 4.
Charge Status Indication
A fast charge in progress is uniquely indicated when the
LED pin goes low. The LED pin is driven to the high-Z
state for all conditions other than fast charge. Figure 2
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 bq2002/F continues
to pulse-trickle charge the battery per the TM selection.
When INH returns low, charge control and the charge
timer resume from the point where INH became active.
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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