If the power is cut, is the micro controller use battery power automatically?

[KKIM.6]

I'm developing STM32WB55VQ power system but I wonder the microcontroller automatically use battery power or not when Vdd is cut.

Is there anybody can explain this?

[KKIM.6]

I have more big issue regarding SMPS in microcontroller.

Can I use the SMPS as AC-DC converter to power microcontroller?

[Andrew Neil]

Please keep to one question per thread.

If your question here about battery power is answered, please mark the solution.

"Can I use the SMPS as AC-DC converter to power microcontroller?"

Start a new thread for a new question.

Have you studied the datasheet description of what the SMPS does?

You can always give links between threads for reference.

[Andrew Neil]

@KKIM.6​  " I didn't know that the wb55 can charge battery."

Really? it's clearly stated in the datasheet:

But note that's only the backup battery/supercap - not any main system supply battery

Note also this diagram showing the different power domains - ie, what gets powered from which supply pins:

@Community member​ "the Data Sheet, might be worth a review"

+99 !

It seems that many (most?) of @KKIM.6​ questions could be answered by a good study of the datasheet and other documentation

https://www.st.com/en/microcontrollers-microprocessors/stm32wb55rg.html#documentation

[Andrew Neil]

"You can always give links between threads for reference"

Like this:

https://community.st.com/s/question/0D53W00001ealDUSAY/can-i-use-smps-in-microcontroller-for-acdc-converter

[KKIM.6]

My final question is whether the power line below is possible or not. 

If it is possible, I don't need PMIC/battery charger between power receiver and microcontroller.

[Andrew Neil · Accepted solution]

again, that's all answered in the datasheet.

 From your other Thread:

[KKIM.6]

I wonder what's happen if apply more than 4 V.​

[Andrew Neil]

Again, the datasheet tells you that.

The 4V is the Absolute Maximum rating; the datasheet defines that term: