NucleoH723 - How to Implement VBAT

[FCamp.1]

Hello,

I need to keep alive an RTC when the system is rebooted and I see there is VBAT pin in the MCU->Nucleo board which I understand is made for it. What I don't understand however is if in the Nucleo I should take out the 0Ohm resistor on SB52 or not to have it working.

Can someone give me the info?

Thanks,

Filippo

[Peter BENSCH · Accepted solution]

UM2407 describes the different modes of solder bridges, including that of SB52:

• SB52=ON: VBAT pin of STM32H7 is connected to VDD_MCU.
• SB52=OFF: VBAT pin of STM32H7 is not connected to VDD_MCU.

The data sheet of the STM32H723 says about VBAT:

To optimize battery duration, this power domain is supplied by VDD when available or by the voltage applied on VBAT pin (when VDD supply is not present). VBAT power is switched when the PDR detects that VDD dropped below the PDR level.

The voltage on the VBAT pin could be provided by an external battery, a supercapacitor or directly by VDD, in which case, the VBAT mode is not functional.

So to use the VBAT function, you must open SB52 and supply VBAT accordingly.

Does it answer your question?

Regards

/Peter

[FCamp.1]

Thanks a lot Peter,

so if i well understood the default condition on the Nucleo board is "or directly by VDD, in which case, the VBAT mode is not functional" which explains why there is the 0 Ohms resistance and why it must be removed to use the actual VBAT function via battery.

This is the point i did not get.

That indeed answers my question.

Cheers,

Filippo