Abstract: A method and system are provided for supplying power to a backup power domain by connecting a battery voltage to a supply terminal for a backup power domain in a low power microcontroller during a startup mode when a main supply voltage, by detecting application of the main supply voltage to the low power microcontroller at a predetermined safe voltage level, and by activating a selection control circuit to power the backup power domain in the low power microcontroller from the main power supply voltage or the backup power supply voltage based on a software-controlled configuration bit, where the selection control circuit is configured to connect, in response to the software-controlled configuration bit having a first user-selected value, the main power supply voltage to the supply terminal for the backup power domain when the main power supply voltage is smaller than the battery power supply voltage.

Abstract: A first voltage scaling power switch is coupled to a first power supply terminal for providing power to a first circuit portion, and a second voltage scaling power switch is coupled between the first power supply terminal providing power to a second circuit portion. A common power rail is coupled the first and second power input nodes during respective voltage scaling modes of the first and second circuit portions. A feedback circuit coupled to the common power rail provides a feedback signal to a control input of the first voltage scaling power switch to regulate a voltage provided by the first power switch, and to a control input of the second voltage scaling power switch to regulate a voltage provided by the second voltage scaling power switch.