BQ24273 Datasheet, PDF (11/27 Pages) Texas Instruments – 2.5A, Single Input, Single Cell Switchmode Li-Ion Battery Charger with Integrated Current Sense

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bq24273
SLUSB08 – JUNE 2012
In addition to the safety timer, the bq24273 contains a watchdog timer that monitors the host through the I²C
interface. Once a read/write is performed on the I²C interface, a 30-second timer (t_WATCHDOG) is started. The 30-
second timer is reset by the host using the I2C interface. This is done by writing a “1” to the reset bit (TMR_RST)
in the control register. The TMR_RST bit is automatically set to “0” when the 30-second timer is reset. This
process continues until battery is fully charged or the safety timer expires. If the 30-second timer expires, the IC
enters DEFAULT mode where the default register values are loaded, the safety timer restarts at 27minutes and
charging continues. The I²C may be accessed again to reinitialize the desired values and restart the watchdog
timer as long as the 27 minute safety timer has not expired. The watchdog timer flow chart is shown in Figure 3.
Start Safety Timer
Yes
Safety timer expired?
No
Charge Done?
ICHG < ITERM
No
Yes ^{STAT = Hi}
Update STAT
bits
No
I2C Read/Write
performed?
Yes
Start 30 second
watchdog timer
Safety timer
fault
Charging suspended
Enter suspended
mode
Fault indicated in
STAT registers
Charge Done?
ICHG < ITERM
Yes ^{STAT = Hi}
Update STAT
bits
No
Safety timer expired?
No
Yes
Safety timer
fault
Reset 30 second
watchdog timer
30s timer expired?
Yes
Charging suspended
Fault indicated in
STAT registers
No
Yes
No
Received SW watchdog
RESET?
Reset to default
values in I2C
register
Restart 27min
safety timer
Figure 3. The Watchdog Timer Flow Chart for bq24273
Hardware Chip Disable Input (CD)
The bq24273 contains a CD input that is used to disable the IC and place the bq24273 into high-impedance
mode. Drive CD low to enable charge and enter normal operation. Drive CD high to disable charge and place the
bq24273 into high-impedance mode. Driving CD high during DEFAULT mode resets the safety timer. Driving CD
high during HOST mode resets the safety timer.
Copyright © 2012, Texas Instruments Incorporated
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