Currently we are looking for the possible approach for Switching between Main supply (LDO) and Vbat Operation.
We have Two backup supplies requirement , Battery and supercap. Either one of the backup supplies is selected but provision should be provided for both (either one of the backup circuit component will be mounted) and other is made DNI(Do not populate)
Super cap back supply is only for RTC and monitor and logging the tampering Events connected to Vbat pin (if Super cap is selected as backup supply by enduser)
we have also have one ADC monitoring 24V from which the 3.3V is derived.
Also there is energy hold up circuit for 3.3V upto 500ms (upto which LDO supplies power to MCU) to shutdown the MCU as soon the Main power outage .
Battery backup is for RTC , Event logging and also the Peripherals and Core of the MCU and it act as a alternate option for short duration when Main Supply (LDO Voltage) is not present
If Battery backup is selected by enduser, then Vbat pin will not be connected to vbat .Does VDD pins Power to Backup circuitry such as RTC? and Tamper GPIOS?
We have considered some of below approaches and provided thoughts on MCU possible operation mode for Battery and main Backup switching circuit, Whether controller can able to detect and differentiate the power source based on 24V Monitoring ADC able to operate between the run mode and Low power mode during Vbat and again resume to run mode when main power is present. or external wakeup interrupt?
Could you please confirm whether our though process is correct with respect to Ability of MCU to switch the operational modes to power safe vbat power?
