7.3.8.1 Host Mode and Default Mode in BQ25910

The BQ25910 is a host controlled charger, and will automatically shut off when the I²C watchdog timer is not reset within the timer period. In default (HIZ) mode, the device automatically disables charging until the host writes the EN_CHG bit high again and resets the watchdog timer via the WD_RST bit. When the charger is in default mode, WD_STAT bit is HIGH. When the charger is in host mode, WD_STAT bit is LOW.

After power-on-reset, the device starts in default mode with watchdog timer expired. All the registers are in the default settings. In default mode, the device remains in HIZ mode and will not charge the battery.

Writing a 1 to the WD_RST bit forces the charger out of default mode and into host mode. All the device parameters can be programmed by the host. To keep the device in host mode, the host has to reset the watchdog timer by writing 1 to WD_RST bit before the watchdog timer expires (WD_STAT bit is set), or disable watchdog timer by setting WATCHDOG bits = 00.

When the watchdog timer is expired (WD_STAT bit = 1), the device returns to default mode and registers are reset to default values except as detailed in the I²C register section. As long as the watchdog timer is expired (WD_STAT bit = 1), the device remains in Default Mode without charging the battery, regardless of the EN_CHG bit state. In order to enable charge after watchdog expired, write WD_RST = 1, and EN_CHG = 1.

Figure 17. Watchdog Timer Flow Chart

The REG_RST bit can be used to reset all of the registers (except STATUS registers) to their default value at any time.