STM32F407 stuck. Latchup? How to find the weakness?

[Lucast]

Hi all,

our product, used in industrial traction, uses an STM32F407 MCU. In certain conditions, very hard to replicate, the MCU stucks and the watchdog does not reset the MCU. It seems completely blocked. 

We're suspecting there are some EMC issue on certain brushed motors used the truck but it is not under our control.  

After we remove the power supply of the board and give back the supply, the board starts to work again.

Someone suggest me some latchup phenomena and I think it could be a possible explanation. Now: how can I find what is the pin (or what are the pins) susceptible to the EMI? There could be some traces the phenomena leaves on the MCU? 

Thanks!

[Ozone]

> Yep. It's full compliant. We replicate some reset on the MCU by using ESD gun at level beyond the level of the normative (i.e. 10-11kV instead of 8kV) but we're not sure it's the same problem because we were not able to replicate the freezing with ESD gun.

If I remember correctly, requiring a power cycle after such an ESD event is normal, and within the allowed range of reactions.

By the way, disruptive EMI can enter the device through exposed communication channels (UART, CAN, etc.), offsetting power supply / ground levels of your MCU board.