SLUUBY1B December 2020 – April 2022 BQ76942
The REG1 and REG2 LDOs take their input from the REGIN pin, which should be approximately 5.5 V. This REGIN pin voltage can be supplied externally (such as by a separate DC/DC converter) or using the integrated voltage preregulator (referring to as REG0), which drives the base of an external NPN BJT (using the BREG pin) to provide the 5.5 V REGIN pin voltage. When the preregulator 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 preregulator is only powered if Settings:Configuration:REG0 Config[REG0_EN] is set, as well as one of Settings:Configuration:REG12 Config[REG1_EN] or Settings:Configuration:REG12 Config[REG2_EN] are set; otherwise, the device does not enable the preregulator.
If neither REG1 nor REG2 will 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.