SLUUCG7 April 2024 BQ76922
The REG1 LDO takes its input from the REGIN pin, which should be approximately 5.5V. This REGIN pin voltage can be supplied externally (such as by a separate DC/DC converter) or using the integrated voltage pre-regulator (referring to as REG0), which drives the base of an external NPN BJT (using the BREG pin) to provide the 5.5V REGIN pin voltage. When the pre-regulator is being used, special care should be taken to ensure the device retains sufficient voltage on its BAT pin, per the device electrical specifications.
The pre-regulator is only powered if Settings:Configuration:REG0 Config[REG0_EN] is set and the Settings:Configuration:REG1 Config[REG1_EN] is set, otherwise the device will not enable the LDO.
If REG1 will not be used in the system, or if the REGIN voltage will be supplied externally, then the Settings:Configuration:REG0 Config[REG0_EN] configuration bit should be cleared.
Note: there is a diode connection between the REGIN pin (anode) and the BAT pin (cathode), so the voltage on REGIN should not exceed the voltage on BAT.