ZHCSJD3B July 2018 – February 2019 BQ25150
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 128us 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 (DPM 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 to the safety timer, the device contains a 50-second I2C watchdog timer that monitors the host through the I2C interface. The watchdog timer is enabled by default and may be enabled by the host through I2C. Once the watchdog timer is enabled, the watchdog timer is started. 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 charger parameters registers (ICHARGE, IPRECHARGE, ITERM,VLOWV, etc) are reset to the default values.