BQ2002ESNTR Datasheet, PDF (5/15 Pages) Texas Instruments – NiCd/NiMH Fast-Charge Management ICs

bq2002E/G
VLBAT = 0.175 ∗ VCC ±20%
The valid temperature range is VTS > VHTF where
VHTF = 0.6 ∗ VCC ±5%.
If the battery voltage or temperature is outside of these
limits, the IC pulse-trickle charges until the next new
charge cycle begins.
If VMCV < VBAT < VPD (see “Low-Power Mode”) when a
new battery is inserted, a delay of 0.35 to 0.9s is imposed
before the new charge cycle begins.
Fast charge continues until termination by one or more of
the five possible termination conditions:
n Peak voltage detection (PVD)
n Negative delta voltage (-∆V)
n Maximum voltage
n Maximum temperature
n Maximum time
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 de-
crease of 2.5mV ±2.5mV terminates fast charge. The PVD
and -∆V tests are valid in the range 1V < VBAT < 2V.
Synchronized Voltage Sampling
Voltage sampling at the BAT pin for PVD and -∆V termi-
nation may be synchronized to an external stimulus us-
ing the INH input. Low-high-low input pulses between
100ns and 3.5ms in width must be applied at the INH
pin with a frequency greater than the “maximum syn-
chronized sampling period” set by the state of the TM
pin as shown in Table 1. Voltage is sampled on the fal-
ling edge of such pulses.
If the time between pulses is greater than the synchro-
nizing period, voltage sampling “free-runs” at once every
17 seconds. A sample is taken by averaging together
voltage measurements taken 57µs 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.
If the INH input remains high for more than 12ms, the
voltage sample history kept by the IC and used for PVD
and -∆V termination decisions is erased and a new his-
tory is started. Such a reset is required when transition-
ing from free-running to synchronized voltage sampling.
The response of the IC to pulses less than 100ns in
width or between 3.5ms and 12ms is indeterminate. Tol-
erance on all timing is ±12%.
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 where
VTCO = 0.5 ∗ VCC ± 5%.
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 before reaching full capacity. With top-off en-
abled, ch arging continues a t a r educed r ate 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 73ms active for
every 1097ms 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 once
every 1.17s for the period specified in Table 1. This re-
sults in a trickle rate of C/32.
TM Pin
The TM pin is a three-level pin used to select the
charge timer, top-off, voltage termination mode, trickle
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