Unable to understand the reason of getting the NUCLEO-F446ZE fried up

[Rainbow2601]

Hello. I was powering up my NUCLEO-F446ZE microcontroller board using an external power supply of 5V. I set the jumper JP3 to E5V. I made some changes in the code and tried to connect the board to the USB to burn the code to its memory. I forgot to remove the external power supply and simply removed the E5V and connected it to U5V. I suddenly inspected that smoke came out of regulator IC U6. Now whenever I am connecting the board to the USB, the over current LED LD5 is blinking and as a result U4 is getting heated up a lot. I know that my Nucleo board has been fried up. Have I made a big mistake with the input power? Can anybody explain me that? Is there any way that this board can be made functional again? Thanks!

[Peter BENSCH · Accepted solution]

What I have understood from your description is

• NUCLEO-F446ZE
• Jumper JP3 to E5V
• external 5V power supply (on pin E5V?)

If by "simply removed the E5V and connected it to U5V" you mean the jumper on JP3, this switches the input voltage. Even if you then still have the external 5V power supply connected to E5V, at best it can still supply the regulator U3 (generates +3V3_ST_LINK) via the wired-or diode D3 if the other voltages at D4 or D5 are not higher.

If smoke came out of the regulator U6, you have overloaded VDD (supply of the STM32F446), the reason for which only you can know.

In principle, you can repair the board - if you have first determined what has been damaged. In the worst case, the STM32F446 is also dead, which would be a major replacement operation. I would try to replace the U6 controller (LD39050PU33R) and then check the board. Otherwise, it's probably easier and cheaper if you get a new NUCLEO.

Hope that helps?

Good luck!
/Peter