Posted on May 12, 2013 at 22:19Does not sound good - but damage may be confined just to that single ADC pin. (we hope you limited the application of ''illegal'' excess voltage to just one pin)
We've been guilty - many others too - but in our case - no more. Our solution was to design a multi-channel, voltage-clamped, buffer/op-amp board - which is unable to output beyond 3V3 to our MCUs under test. We have voltage clamps on both every input channel and redundantly (for safety) upon every output channel. And - should our circuit detect an over-voltage condition - we immediately open a power FET which routes all voltages to our buffer/op-amp board. Not quite to ''space station'' or ''human implantation'' standards - but ''good for Gov't work - in most cases.''
Now in your case - check/double check that the 12V has been safely/properly divided down to ''MCU appropriate'' levels. Suggest that you remove all signals from that suspect pin (recipient of your over-voltage) - does the MCU still over-heat? And - ''finger method'' of heat measure may introduce ESD - along with not providing an ''overly exact/repeatable'' measurement.
If you're lucky - you may be able to salvage many/most of the MCU's other pins. A good measure of the MCU's health may be its current draw - prior to and after abuse. A second M4 demo board enables such a, ''baseline'' measure...
