The BQ76905 device draws its supply current from the BAT pin, which is typically connected to the top-of-the-stack point through a series diode, to protect against any fault within the device resulting in unintended charging of the pack. A series resistor and capacitor is included to lowpass filter fast variations on the stack voltage. During a short circuit event, the stack voltage may be momentarily pulled to a very low voltage before the protection FETs are disabled. In this case, the charge on the BAT pin capacitor temporarily supports the BQ76905 device's supply current to avoid the device losing power.

The REGSRC pin serves as the supply voltage for the integrated REGOUT customer regulator and for the CHG and DSG FET drivers. This pin can also be connected to the top of stack through a diode, to similarly allow the voltage to hold up longer during a short circuit event. If a diode or any series resistance (> 1 Ω) is included between the top of stack and the REGSRC pin, a minimum 1-μF capacitor is recommended to be included at the REGSRC pin to VSS. It is also acceptable to short the REGSRC pin to the BAT pin, such that the same diode and filter circuit can support both pins. However, the system designer should consider the load on the REGOUT pin discharges the BAT capacitor faster in this case.