NUCLEO-H723ZG External supply 3.3V problem

[TOsso.1]

Hey

I work with NUCLEO-H723ZG and I try to work with 3.3V External power supply.

I try to connect the board according to the datasheet:

and I saw few problems:

1. My code is not working. I proggram simple code of blinking. when I work with 5V (external/usb) I can see the blinking but when I work with External 3.3V I can't see nothing. I also try code with toggle some gpio (not led) and measure with oscilloscope. I get the same resault, when the supply is 5V I saw the GPIO toggle and when I use External 3.3V I don't see nothing.

2. When I use External 3.3V the LED5 is turn-on. I don't understand why because we can see in the datasheet that only the 5V is connect to LED5:

Thank you very much

[Tesla DeLorean]

>> I don't understand why because we can see in the datasheet that only the 5V is connect to LED2

Shows schematic section for LED5 (LD5) ....

[TOsso.1]

You're right. My mistake. I meant LED5

I fixed it in the post. Thank you

[TDK]

If ST-Link chip isn't powered, you will need to disconnect the NRST lines between them otherwise it will be held in reset.

The user manual usually has a few paragraphs explaining the external power options.

Edit:

Here, JP3 needs removed.

[TOsso.1]

Hey. Thank you about the answer

I think I try this and is not help me ( I will check again later).

And how the LED5 is turn-on?

[TDK]

Most LDO voltage regulators can be backpowered to some extent. It doesn't take much current for an LED to turn on, so that's probably why it's lighting up. Measure the voltage on the 5 V rail in such a situation, likely it's just below the 3.3 V rail.

Edit:

Also note that the st-link isn't on, it won't be sending the 8 MHz signal to the main processor, so you can't rely on it for a clock. You'll need to use the internal HSI.