The device has a built-in fast charge safety timer to prevent extended charging cycle due to abnormal battery conditions. The user can program fast charge safety timer through CHG_TMR register bits. When safety timer expires, charging should stop through setting CHARGE_CURRENT() to 0A. The status register CHG_TMR_STAT bit is set to 1 and CHRG_STAT bits will be set to 000b(not charging), and CHRG_OK pin can be configured to be pulled low for minimum 256us to inform host if CHRG_OK_INT=1b. CHG_TMR_STAT bit will keep its 1b status until safety timer gets reset. The safety timer feature can be disabled by clearing EN_CHG_TMR bit.

During IINDPM and VINDPM regulation, or TREG thermal regulation, the safety timer counts at half clock rate as the actual charge current is likely to be below the programmed setting. For example, if the charger is in input current regulation throughout the whole charging cycle, and the safety timer is set to 5 hours, then the timer will expire in 10 hours. This half clock rate feature can be disabled by setting EN_TMR2X = 0. Changing the EN_TMR2X bit while the device is running has no effect on the safety timer count, other than forcing the timer to count at half the rate under the conditions dictated above. The deglitch times for determining IINDPM active and VINDPM active is 1ms, and deglitch times for determining TREG active is 10ms.

During faults which disable charging, timer is suspended. Since the timer is not counting in this state, the EN_TMR2X bit has no effect. Once the fault goes away, safety timer resumes. If the charging cycle is stopped and started again, the timer gets reset (toggle CHRG_INHIBIT bit restarts the timer, change CHARGE_CURRENT() register from non zero to zero and then non zero, charged battery falls below recharge threshold after termination).

The safety timer is reset for the following events:

1. Charging cycle stop and restart (toggle CHRG_INHIBIT bit, or charge-terminated battery falls below recharge threshold after termination, or change CHARGE_CURRENT() register from zero and then non zero)
2. BAT voltage changes from pre-charge to fast-charge or vice versa
3. Safety Timer (CHG_TMR[1:0]) register bits are changed
4. Toggle EN_CHG_TMR bit, when EN_CHG_TMR becomes 0b, the safety timer should be reset and count from beginning when re-enable again(EN_CHG_TMR=1b)

The pre-charge safety timer (fixed 2hr counter that runs when VBAT < VSYS_MIN()), follows the same rules as the fast-charge safety timer in terms of getting suspended, reset, and counting at half-rate when EN_TMR2X is set. Note pre-charge safety timer applies to both pre-charge and trickle charge phase.