Hardware/schematic issue: My design is destroying microcontrollers, why?

[MLind.3]

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!

[Tesla DeLorean]

I would suggest walking the pin list vs the data sheet, see if you have any anomalies.

Go over the netlist generated by the schematic tool. Probe nets on unpopulated board.

Fab a minimal board, basically F407 plus VCAP capacitors. Power at VCC jumper, determine power draw.

Be sure of part orientation.

[Uwe Bonnes]

It is no good idea to keep VBAT open. However I do not think that it is fatal.

[SKacp.1]

Hi,

Why do You think that microcontroller is destroyed?

What happens when power is connected?

Where is connected VCC?

I see that in the diagram You do not have connected BOOT1 (PB2) to the GND by resistor 10k.

[MLind.3]

@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!

[SKacp.1]

Hi,

Please check the polarity of the tantulum capacitors if You using. I had similiar problem as they was soldered backwards

[Uwe Bonnes]

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.

[TDK]

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.

[MLind.3]

Thanks everyone for your input and suggestions, i will try them out during the day.

[MLind.3]

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!