PIC pin suffering ESD damage?

[treez]

Hi

We have a PIC16F18856 with Vcc = 3v3.

The code takes pin A0 high…however, pin A0 only goes high when the pin is totally unloaded.
If I load it with 10k, it goes up to about 0.1v
If I load it with 92k, it goes up to about 0.5v
If I load it with 174k, it goes up to around 0.9v

Does this sound like a pin suffering ESD damage?
The micro works and the other pins work fine.
Or would you say the pad for A0 pin is likely to be almost dry joint and offering high resistance to the external circuit?

 

[dick_freebird]

A dry joint ought to impose the same problem for the output
low state, loaded against Vdd. This theory could easily be tested
with a soldering iron and somebody's steady-enough hand.
Unless it's a BGA or some similarly difficult package style.

High side output driver could be fried. ESD signature can be open,
short or resistive (not necessarily linear). So, you're welcome.

Pulling I-V curves for known good and suspected bad A_ outputs
ought to be able to say whether A0 is out-of-family. Probing the
package lead rather than some remote connector is also a good
diagnostic "cut".

Opinions of what's possible are worth much less than bench data
taken to an orderly debug plan.

 

[pjmelect]

PIC devices are extremely tough, and it is not likely that it is damaged by ESD or mistreatment. The only way to damage a PIC IO pin is to supply it with a excessively high or negative voltage. A more likely explanation of your problem is that the pin is open collector because you have not set the ODCONA register low.

 

[betwixt]

I have to agree with pjmelect, they are hard to kill accidentally. I recently found one fitted in it's socket backwards, it smelled hot and was far too hot to touch. The tech let it cool down, reversed it and switched on again - the product passed all tests!

You symptoms do suggest the output driver is disabled in software and only the weak pull-up is producing the logic high when unloaded.

Brian.