Robust Fail-Safe System for Prolonging the Backup Battery Life in Real-Time Low Power MCU Systems

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.