8.3.4.6 Charging Safety Timer

The device has built-in safety timer to prevent extended charging cycle due to abnormal battery conditions. The user can program fast charge safety timer through I²C (CHG_TIMER bits). When safety timer expires, the fault register TMR_STAT bit is set to 1, and an INT pulse is asserted to the host. The safety timer feature can be disabled by clearing EN_TIMER bit.

During input voltage, current or thermal regulation or cell balancing active mode (cell balancing discharging), the safety timer counts at half clock rate as the actual charge current is likely to be below the register setting. For example, if the charger is in input current regulation (IINDPM_STAT=1) throughout the whole charging cycle, and the safety timer is set to 12 hours, then the timer will expire in 24 hours. This half clock rate feature can be disabled by setting TMR2X_EN = 0. Changing the TMR2X_EN 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.

During faults which disable charging, or supplement mode, timer is suspended. Since the timer is not counting in this state, the TMR2X_EN 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.

The safety timer is reset for the following events:

1. Charging cycle stop and restart (toggle CD pin, EN_CHG bit, or charged battery falls below recharge threshold).
2. BAT voltage changes from pre-charge to fast-charge or vice versa (in host-mode or default mode).

The precharge safety timer (fixed 2hr counter that runs when VBAT < V_{BAT_LOWV}), follows the same rules as the fast-charge safety timer in terms of getting suspended, reset, and counting at half-rate when TMR2X_EN is set.