Datasheet

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-chargephase.
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 260µsofa
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 V
SS
or by selecting Mode 2 in the dis
-
play.
Charge Status Indication
Charge status is indicated by the LED
1
and LED
2
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 V
CELL
exceeds the voltage at the MCV
pin, both LED
1
and LED
2
outputs are held low regard
-
less of other conditions. Both can be used to directly
drive an LED.
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 regulatedcurrentsource.
When used in switch mode configuration, the nominal
regulated current is:
I
REG
= 0.225V/R
SNS
Charge current is monitored at the SNS input by the
voltage drop across a sense resistor, R
SNS
, between the
low side of the battery pack and ground. R
SNS
is sized to
provide the desired fast charge current.
If the voltage at the SNS pin is less than V
SNSLO
, the
MOD output is switched high to pass charge current to
the battery.
When the SNS voltage is greater than V
SNSHI
, the MOD
output is switched low—shutting off charging current to
the battery.
V
SNSLO
= 0.04 ∗ V
CC
± 25mV
V
SNSHI
= 0.05 ∗ V
CC
± 25mV
When used to gate an externally regulated current
source, the SNS pin is connected to V
SS
, and no sense re-
sisitor is required.
7
bq2004E/H