SLUUCW9 December 2023 BQ76972
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 in use, 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 are used in the system or if the REGIN voltage is supplied externally, clear the Settings:Configuration:REG0 Config[REG0_EN] configuration bit.