BQ24180_1 Datasheet, PDF (19/41 Pages) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and Accessory Power Connection

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bq24180
SLUSA02 A – FEBRUARY 2010 – REVISED FEBRUARY 2010
Begin DEFAULT
Mode Battery
Charge Cycle
Reset safety timer to
27min and start
Yes
Safety Timer expired?
No
Safety timer
fault
Charging suspended
Enter suspended
mode
Fault indicated in
STAT registers
PSEL = Hi?
No
PC Mode
AC Adapter
Yes
Mode
(AAM)
Load default values to
I2C registers.
No Input Current Limit
STAT = 0
Load PC default
values for input
current limit from I2C
registers.
STAT = 0
No
No _{Load Optimized Charge}
Parameters?
Yes
Begin HOST Mode
Battery Charging
Figure 29. DEFAULT Mode Charging Process
Safety Timer and Watchdog Timer in Charge Mode
At the beginning of charging process, the bq24180 starts the safety timer. This timer is active during the entire
charging process. If charging has not terminated before the safety timer expires, the IC enters suspend mode
where charging is halted. The safety timer time 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. The EN bit or
power must be toggled in order to clear the safety timer fault. The safety timer duration is selectable using the
TMR_X bits in the V_IN-DPM Voltage/ Safety Timer Register. Changing the safety timer duration resets the safety
timer.
In addition to the safety timer, the bq24180 contains a watchdog timer that monitors the host through the I²C
interface. Once a read/write is performed on the I²C interface, a 12-second timer (t_WATCHDOG) is started. The
12-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 12-second timer is
reset. This process continues until battery is fully charged or the safety timer expires. If the 12-second timer
expires, the IC enters DEFAULT mode where the default charge parameters 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 as long as the 27 minute safety timer has not expired. Once the safety timer expires,
charging is disabled. This function prevents continuous charging of a defective battery if the host fails to reset the
safety timer. The watchdog timer flow chart is shown in Figure 30.
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