Datasheet

bq24401
2
RC
7
6
V
SS
V
CC
C
MTO
R
MTO
MTO MTO
MTO = R C 35,988´ ´
bq24401
2
7
Battery
Pack
5
TS
N
T
C
V
SS
V
CC
V
CC
R
T1
R
T2
bq24401
www.ti.com SLUS497A –SEPTEMBER 2001–REVISED MARCH 2010
Maximum Charge Time
The bq24401 sets the maximum charge-time through the RC pin. With the proper selection of external resistor
and capacitor values, various time-out values may be achieved. If the timer expires while still in fast charge, the
bq24401 proceeds to top-off charge (if top-off is enabled) or trickle maintenance charge. If top-off is enabled, the
timer is reset on the completion of fast charge before beginning top-off charge. Figure 3 shows a typical
connection.
Figure 3. Typical Connection for the RC Input
The following equation shows the relationship between the R
MTO
and C
MTO
values and the maximum charge time
(MTO) for the bq24401:
(2)
MTO is measured in minutes, R
MTO
in ohms, and C
MTO
in farads. (Note: R
MTO
and C
MTO
values also determine
other features of the device. See Table 4 for details.)
If, during fast charge, V
TS
> V
LTF
, then the timer is paused and the IC enters battery conditioning charge until V
TS
< V
LTF
. Since the IC is in the battery conditioning state, the LED flashes at the 1 Hz rate. Once V
TS
<V
LTF
, fast
charge restarts and the timer resumes from where it left off with no change in total fast charge time.
Maximum Temperature
A negative-coefficient thermistor, referenced to V
SS
and placed in thermal contact with the battery, may be used
as a temperature-sensing device. Figure 4 shows a typical temperature-sensing circuit.
Figure 4. Temperature Monitoring Configuration
During fast charge, the bq24401 compares the battery temperature to an internal high-temperature cutoff
threshold, V
TCO
, and a low-temperature threshold, V
LTF
. During fast charge only, the V
HTF
fault comparator is
Copyright © 2001–2010, Texas Instruments Incorporated Submit Documentation Feedback 7
Product Folder Link(s): bq24401