STM32F401re external power

[Maximiliano]

Hello everyone.

I'm trying to run my project with external power supply (5V on Vin or E5V) but the problem is that I always have to press the reset button to start the code normally when I connect it, if the board is powered by the USB port the program starts without any problem without pressing the reset button once.
What can be happening that generates this behavior?

Another separate question I had is if when I put the Jp5 pin to feed with E5V can I have at the same time connected the USB to debug? I would try it but there is little time left to finish the project and if it burns I could not get another one so fast.

Thank you very much.

[liaifat85]

As far as I know the  external power supply for STM32F401re Nucleo board  is 7V > & < 12V. 

[Maximiliano]

Sorry, 5V on E5V. what you say is correct for the VIN pin.

[AScha.3]

look at the circuit ...then you see, what you connect.

https://www.st.com/en/evaluation-tools/nucleo-f401re.html#cad-resources

seems ok to connect both. 🙂

[Maximiliano]

thank you for your reply AScha.3

I am just using this schematic as a guide. I am attaching screenshots where apparently it is the same to feed by USB or E5V but for some reason it generates a different effect.

or did you mean that it is OK in the second question to connect via USB while JP5 is configured to power the board with external 5V on E5V?

[AScha.3]

right. JP5 on 2-3 powers the F401 by external 5V .

and the stlink also - or by usb (by the diodes d2, d3 ).

[Piranha · Accepted solution]

https://community.st.com/t5/stm32-mcus-boards-and-hardware/stm32f767zi-on-external-power-supply-is-stuck-until-reset-button/td-p/115194

[Maximiliano]

Thank you very much for the answer, I was able to use the HSI and it works with external power supply without using the reset button which is the important thing!.

I don't know if I understand the reason for the failure, it is something related to the HSE startup times when using external power supply, right?
(I was translating)

[Piranha]

The HSE starts quickly, but ST-LINK firmware provides a clock for HSE only after 2 second delay. You have to adjust your code to deal with that delay.