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ESD and STM32F407

Question asked by miller.dave on Mar 5, 2014
Latest reply on Mar 5, 2014 by miller.dave
It's ESD season once again. I have been getting far too many STM32-F407 TQPF IC's being blown up. I believe ESD is the culprit. Failure mode is a bit used as an input is blowing out the internal pullup or that what it looks like. The pin on a bad board is sitting a 0V where a good board is pulled up.

The pins are being used as a rotary encoder input. Pin PC5,PC6,PC7 and PB4, PB5, PB6.
From what I can read the part is a class 2 device for ESD.

What is disconcerting is I am still getting failures after I tack PESD0603-24 Diodes across the pins to  ground at the encoder. This should solve the issues but it does not seem to. They are specifically designed as ESD diodes.

I have added on the next run of PCB's NUF4402MN devices but have many boards out there to support.

Any suggestions are appreciated. I see, to be missing something.
Thanks
Dave

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