9.3.15 Safety Timer and Watchdog Timer

At the beginning of the charge cycle, the device starts the safety timer. If charging has not terminated before the programmed safety time, t_MAXCHG, expires, the device enters idle mode and charging is disabled. The pre-charge safety time, t_PRECHG, is 10% of t_MAXCHG. When a safety timer fault occurs, a single 128 µs pulse is sent on the INT pin and the STAT and FAULT bits of the status registers are updated over I²C. The CD pin or power must be toggled in order to clear the safety timer fault. The safety timer duration is programmable using the TMR 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 enables the 2X timer function to prevent premature safety timer expiration when the charge current is reduced by a load on PMID, SYS, LS/LDO or a NTC condition. When t_{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 to the safety timer, the device contains a 50-second watchdog timer that monitors the host through the I²C interface. Only after an I²C transaction is performed on the I²C interface, will the watchdog timer start. In the case where the device is set to operate in High Impedance Mode, the watchdog timer is automatically disabled and can only be re-started after the device exits the High Impedance Mode and a subsequent I²C transaction is performed. The watchdog timer is reset by any transaction by the host using the I²C interface. If the watchdog timer expires without a reset from the I²C interface, all registers except MRRESET_VIN and MRREC are reset to the default values.