BQ2004E_07 Datasheet, PDF (7/19 Pages) Texas Instruments – Fast-Charge ICs

bq2004E/H
Maximum charge time is configured using the TM pin.
Time settings are available for corresponding charge
rates of C/4, C/2, 1C, and 2C. Maximum time-out termi-
nation 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 the C/2 through 4C
rates. This phase may be necessary on NiMH or other
battery 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 equal to
0.235∗ the fast-charge safety time (See Table 1.) Dur-
ing top-off, the MOD pin is enabled at a duty cycle of
260µs active for every 1820µs inactive. This modula-
tion results in an average rate 1/8th that of the fast
charge rate. Maximum voltage, time, and temperature
are the only termination methods enabled during top-
off.
Pulse-Trickle Charge
Pulse-trickle charging may be configured to follow the
fast charge and optional top-off charge phases to com-
pensate for self-discharge of the battery while it is idle
in the charger.
In the pulse-trickle mode, MOD is active for 260µs of a
period specified by the settings of TM1 and TM2. See
Table 1. The resulting trickle-charge rate is C/512.
Both pulse trickle and top-off may be disabled by tying
TM1 and TM2 to VSS or by selecting Mode 2 in the dis-
play.
Charge Current Control
The bq2004E/H controls charge current through the MOD
output pin. The current control circuitry is designed to sup-
port implementation of a constant-current switching regulator
or to gate an externally regulated current source.
When used in switch mode configuration, the nominal
regulated current is:
IREG = 0.225V/RSNS
Charge current is monitored at the SNS input by the
voltage drop across a sense resistor, RSNS, between the
low side of the battery pack and ground. RSNS is sized to
provide the desired fast charge current.
If the voltage at the SNS pin is less than VSNSLO, the
MOD output is switched high to pass charge current to
the battery.
When the SNS voltage is greater than VSNSHI, the MOD
output is switched low—shutting off charging current to
the battery.
VSNSLO = 0.04 ∗ VCC ± 25mV
VSNSHI = 0.05 ∗ VCC ± 25mV
When used to gate an externally regulated current
source, the SNS pin is connected to VSS, and no sense re-
sisitor is required.
Charge Status Indication
Charge status is indicated by the LED1 and LED2 out-
puts. The state of these outputs in the various charge cy-
cle phases is given in Table 2 and illustrated in Figure 3.
In all cases, if VCELL exceeds the voltage at the MCV
pin, both LED1 and LED2 outputs are held low regard-
less of other conditions. Both can be used to directly
drive an LED.
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