SLUSDU0 September 2019 BQ21061
At the beginning of the charge cycle, the device starts the safety timer. If charging has not terminated before the programmed safety time, tMAXCHG, expires, charging is disabled. The pre-charge safety time, tPRECHG, is 25% of tMAXCHG. When a safety timer fault occurs, a single 128-µs pulse is sent on the INT pin and the SAFETY_TMR_FAULT_FLAG bit in the FLAG3 register is updated over I2C. The CE pin or input power must be toggled in order to reset the safety timer and exit the fault condition. Note that the flag bit will be reset when the bit is read by the host even if the fault has not been cleared. The safety timer duration is programmable using the SAFETY_TIMER bits. When the safety timer is active, changing the safety timer duration resets the safety timer. The device also contains a 2X_TIMER bit that doubles the timer duration prevent premature safety timer expiration when the charge current is reduced by a high load on PMID (DPPM operation), VIN DPM, thermal regulation, or a NTC (JEITA) condition. When 2X_TIMER function is enabled, the timer is allowed to run at half speed when any loop is active other than CC or CV.
In addition, the BQ21061 has a 50s watchdog timer which resets after every I2C transaction. This feature, which is enabled by default, resets all charger parameters registers to their default values when the timer expires.