STM32G0 Nucleo MB1455C board does not run on 5V supply

[KPN1]

Hi There,

I am using a STM32G0 Nucleo MB1455C board with STM32G031K8 processor.

Firmware loads ok through USB and runs as intended.

For my target application I want to power the board from a 5V supply. According to the user manual that should be possible without any changes to the solder bridges on the board.

However when I connect 5V to CN4 pin 4 the red power LED LD2 lights up, 3V3 is present but the processor does not start. It runs when I put 8V onto the Vin pin (CN4 pin 1).

This feels like a configuration issue, but the manual seems to indicate this is not needed. A schematic would go a long way, but I could not find one for this board.

Any idea what needs to change for the 5V power input to work?

Appreciate your assistance.

Regards, Peter

[mfgkw]

Hi Peter,

the schematics goes here: https://www.st.com/resource/en/schematic_pack/mb1455-g031k8-c01_schematic.pdf

[KPN1]

Thanks for the schematic link.

Looking at this, the 5V on CN4 pin 4 does not power the regulator for the ST-Link processor. The diodes prevent that.

Not that I need that in normal operation, but the ST-Link connection is likely what is holding the reset down and stopping the micro from running.

I could bridge the diode D5 to feed the 5V back to the E5V rail that powers the U1 regulator for the ST Link section. Any better ideas?

Regards, Peter