The BQ76907 provides a signal that indicates if the CHG pin voltage is above a level of approximately 2 V. The raw value of this flag can be read through the communications interface, and an alarm can be generated on the ALERT pin whenever the debounced version of this flag changes state, based on device settings. This flag can be used by the system to assist in recovery from a current fault condition.

The CHG Detector signal is enabled and evaluated by logic within the device if Settings:Configuration:FET Options[CHGDETEN] = 1. The value of the raw CHG Detector output can be read over the serial communications interface at Alarm Raw Status()[CDRAW]. If the CHG Detector output is stable for a time interval in excess of Settings:Configuration:CHG Detector Time, its value is latched into Battery Status()[CHGDETFLAG], which is a debounced version of the CHG Detector signal. The Alarm Status()[CDTOGGLE] is set whenever the debounced signal (CHGDETFLAG) changes from its previous debounced state. The value of Settings:Configuration:CHG Detector Time is programmable from 100 ms to 25.5 s in steps of 100 ms

The host can use the Alarm Enable()[CDTOGGLE] bit to mask the alarm. When Alarm Status()[CDTOGGLE] is set, the host can write a 1 to Alarm Status()[CDTOGGLE] to clear the alarm. If [CHGDETEN] is set, then whenever the CHG Detector output changes state from the debounced latched version, the LFO is wakened to begin timing it (if the LFO is otherwise off in DEEPSLEEP). If in DEEPSLEEP, the LFO can be disabled after timing a new debounced version, based on the setting Settings:Configuration:Power Config[DPSLP_LFO].

When a current fault occurs in a system, such as a short circuit event, the device generally disables the DSG FET, the CHG FET, or possibly both, depending on settings. The device can be configured to wait a programmed delay then reenable the FETs. If the current fault condition is still present, then a new fault is triggered, and the FETs disabled again. If a fault persists, this cycle of periodically recovering and retriggering a fault can continue indefinitely, which is generally not acceptable.

An alternative is to only allow a limited number of retries, then to disable further retries after that limit is reached. This capability is supported using the Current Protection Latch. This avoids the indefinite cycle of retries, but then can render the pack unusable after a limited number of retries.

If the pack is removable, such as in a power tool, then another option is to keep the FETs disabled until the pack has been removed from the system. In this case, if the CHG driver is disabled and a charger is not connected, then the CHG pin is pulled up to the PACK+ voltage while a load is connected, resulting in the CHG Detector signal being asserted. When the pack is removed from the system (and the charger is still not connected), then the CHG pin generally falls to near the BAT- voltage level, resulting in the CHG Detector signal being deasserted. A host processor within the battery pack can then use this signal to trigger recovery of the pack.

Note that the use of this CHG Detector for load removal is dependent on the system configuration and is not necessarily usable in all cases. Thus, it is important for the pack designer to evaluate whether it is applicable to the system or not.