BQ2004 Datasheet, PDF (6/15 Pages) Texas Instruments – Fast-Charge IC

bq2004
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
the fast-charge safety time (See Table 1.) During top-
off, the MOD pin is enabled at a duty cycle of 260µs ac-
tive for every 1820µs inactive. This modulation 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 follows the fast charge and op-
tional top-off charge phases to compensate for self-
discharge of the battery while it is idle in the charger.
The configured pulse-trickle rate is also applied in the
charge pending state to raise the voltage of an over-
discharged battery up to the minimum required before
fast charge can begin.
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/64 when
top-off is enabled and C/32 when top-off is disabled.
Both pulse trickle and top-off may be disabled by tying
TM1 and TM2 to VSS.
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 2.
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.
Charge Current Control
The bq2004 controls charge current through the MOD
output pin. The current control circuitry is designed to
support 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.
Table 1. Fast-Charge Safety Time/Hold-Off/Top-Off Table
Corresponding
Fast-Charge
Rate
C/4
C/2
1C
2C
4C
C/2
1C
2C
4C
TM1
Low
Float
High
Low
Float
High
Low
Float
High
TM2
Low
Low
Low
Float
Float
Float
High
High
High
Typical
Typical
Fast-Charge Safety PVD, -∆ V Hold-Off Top-Off
Time (minutes)
Time (seconds) Rate
Pulse-
Trickle
Rate
360
137
Disabled Disabled
180
820
Disabled C/32
90
410
Disabled C/32
45
200
Disabled C/32
23
100
Disabled C/32
180
820
C/16
C/64
90
410
C/8
C/64
45
200
C/4
C/64
23
100
C/2
C/64
Pulse-
Trickle
Period (Hz)
Disabled
240
120
60
30
120
60
30
15
Note:
Typical conditions = 25°C, VCC = 5.0V.
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