bq24160, bq24161
bq24163, bq24168
SLUSAO0A –NOVEMBER 2011–REVISED MARCH 2012
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Safety Timer and Watchdog Timer (bq24160/ bq24161/ bq24163 only)
At the beginning of charging process, the bq24160/1/3 starts the safety timer. This timer is active during the
entire charging process. If charging has not terminated before the safety timer expires, charging is halted and the
CE bit is written to a “1”. The length of the safety timer is selectable using the I2C interface. A single 128μs pulse
is sent on the STAT and INT outputs and the STATx bits of the status registers are updated in the I2C. In
DEFAULT mode, the safety timer can be reset and a new charge initiated by removing/inserting the input supply
or toggling the CD pin. In HOST mode, the CE bit is set to a '1' when the safety timer expires. The CE bit must
be cleared to a '0' in order to resume charging and clear the safety timer fault. The safety timer duration is
selectable using the TMR_X bits in the Safety Timer Register/ NTC Monitor register. Changing the safety timer
duration resets the safety timer. This function prevents continuous charging of a defective battery.
In addition to the safety timer, the bq24160/1/3 contain 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 (tWATCHDOG) 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 the 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 27 minutes
and charging continues. The I2C may be accessed again to reinitialize the desired values and restart the
watchdog timer. The watchdog timer flow chart is shown in Figure 24.
Start Safety Timer
Yes
Safety timer expired?
fault
Safety timer
No
Charging suspended
Enter suspended
STAT = Hi
Update STAT
bits
Yes
Charge Done?
ICHG < ITERM
mode
Fault indicated in
STAT registers
No
No
I2C Read/Write
performed?
Yes
Start 30 second
watchdog timer
Reset 30 second
watchdog timer
STAT = Hi
Update STAT
bits
Yes
Charge Done?
ICHG < ITERM
No
Yes
Safety timer
fault
Safety timer expired?
No
Charging suspended
Fault indicated in
STAT registers
No
Yes
Received SW watchdog
RESET?
No
30s timer expired?
Yes
Reset to default
values in I2C
register
Restart 27min
safety timer
Figure 24. The Watchdog Timer Flow Chart for bq2416x
20
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Product Folder Link(s): bq24160 bq24161 bq24163 bq24168
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