SLUSCU0I March 2018 – September 2020 BQ77915
The BQ77915 device has two dedicated pins (PRES and LPWR) for HIBERNATE mode operation. Most of the internal circuitry is turned off in HIBERNATE mode to save power. Charge and discharge FETs are turned off and all fault protections are disabled.
The PRES pin has an internal pulldown connected to the pin, which pulls PRES low. When the PRES pin is left floating (the system or charger is not connected to the pack), the load is not connected, and the device is not in any fault condition, the device enters HIBERNATE mode after tPRES_DEG_ENT time. Once in HIBERNATE mode, the system or the charger should drive this pin high (>VPRESH) through the resistor R2 for NORMAL mode operation. When the battery pack (in HIBERNATE mode) is inserted to the tool/system or when a charger is connected to the pack, the system has to provide a pull-up to the PRES pin, which puts the device back to NORMAL mode. The device will exit HIBERNATE mode after a tPRES_DEG_EXT deglitch time.
In a stacked configuration, connect the LPWR pin of an upper device to the PRES pin of a lower device through the resistor R3.