I have had the PCB professionally produced for this prototype board. But for some reason every time i try to build the board, the STM32F407 microcontroller gets destroyed at power on. I have narrowed it down to when i populate the filter on the VDDA/VREF+ pins. What is wrong with my schematic? Also, thanks community for being a wealth of information for many years!
@clive1, thank you for good suggestions! The boards have been thouroughly checked, both at the producing factory and by myself. So it looks like the boards conform to the schematic.
@SKacp.1, I realized after posting that i should have been more clear on this point. At power on, i see a large (180 - 200 mA) current draw. After that, VCC is shorted to ground. A post-mortem removal of microcontroller from board also show VCC shorted to ground internally. On all power pins.
To answer your other question, VCC is connected, via a jumper, to voltage regulator 3.3V. I have measured the voltage and it is 3.35V and very stable.
I was hoping i had made an obvious blunder in the schematic, investigation will have to continue. Thank you all for your help so far!
Check carefully that there is not unwanted connection from 12 Volt to any pin or from 5 Volt to a not 5 Volt tolerant pin. I only destroyed STM32s by having a to high voltage on some pin.
I would tie VDD directly to VDDA to rule out issue with the filter/powerup arrangement. There is a requirement between the two rails on powerup that you are probably violating. You can fix this by putting a schottky diode from VDD to VDDA.
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I finally managed to get my board working. Though i am sad to say i have no idea why five consecutive boards broke and this sixth one works. So no real conclusion i am afraid. Huge thanks to the community however for your eagerness to help a poor bloke out!
