Nucleo-H753ZI Power Supply through 5V

[SamuLibero]

Hi everyone,

I’m currently struggling to understand the behavior of the power line on the Nucleo-H753ZI board.

My goal:

The Nucleo board should be programmable via CN1 (Micro USB, ST-Link connection to PC). When connected, this should provide both 3.3V and 5V.

While maintaining this connection, I want to enable an external switch to power the board via a Power Delivery (PD) power bank, which supplies 5V.

The idea is that the CN1 connection can then be disconnected without causing a reset or power loss, as long as external power is already connected.

What I observed experimentally:

• Jumper on the board is set to “ST-Link” position.

• With CN1 connected to the PC, CN8 pin 7 and pin 9 provide 3.3V and 5V, respectively (as per the datasheet).

• When I connect an external 5V PD power supply to CN8 pin 9, I don’t see any overcurrent issues.

• If I disconnect the CN1 connection, the board stays powered, and the running programs continue without interruption.

• Probing CN8 pin 7, I can confirm that the board still provides a proper 3.3V output, so the step-down from 5V appears to be working correctly.

My concern:

Although this setup works in practice (and I’ve also seen similar implementations in older designs), I couldn’t find any references in the manuals or documentation confirming that this behavior is officially supported.

Does anyone have more detailed insights on this? Is this usage considered safe and acceptable, or are there recommended alternatives?

Please note that I’m relatively new to the field, so any feedback or clarification would be very appreciated.

Thanks in advance!

[mbarg.1]

Double check on board schematic - a pdf is in STM site for download and you will see that there is a diode network for power

[TDK]

> Although this setup works in practice (and I’ve also seen similar implementations in older designs), I couldn’t find any references in the manuals or documentation confirming that this behavior is officially supported.

As long as the board remains powered, it will not reset spontaneously. The power supplies on that board have diodes which power the 3.3V rail from multiple sources. Only one needs to be active to keep the chip alive.

This isn't really a chip feature, it's just hardware. The chip doesn't know or are where the power comes from, only that it's there and is stable. Perfectly fine to switch between sources.