I just shot off a trouble ticket to Microchip about my 18F4610 PIC. I'm pasting a copy of what I told them here to see if any of you have run into this kind of problem with other PIC chips.

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I've been using the 18F4610 very successfully in a controller board project for some months now. Yesterday, I noticed the L7805CV voltage regulator that creates +5v power for the chip was overheating. I unplugged all of the IC chips from the board and the overheating stopped. I then started looking for the source of the problem and it happens that the 18F4610 chip was heating up when it was plugged into the board. At that point I started looking for potential shorts on the board and didn't find any.

I finally started checking the 18F4610 chip itself and discovered that for the two of these chips that I had been using the resistance between VSS (pin 31) and VDD (pin 32) was between 10-15 ohms. I got a fresh 18F4610 chip out of my inventory and discovered that the resistance between VSS and VDD was a bit above 4.7K ohms. I plugged the fresh 18F4610 chip into the board and powered it up and there was no overheating.

Do you have any idea how this could have happened? If I hadn't accidently put my finger on the voltage regulator and discovered that it was blazing hot I would have never noticed the problem. The 18F4610 chips were otherwise performing quite well and I was communicating with them via the UART serial link.

Is this a chip failure or is there some way that I could have treated the chips to have cause this sort of behaviour?

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If anybody has either had this sort of experience or heard of it before I'd appreciate hearing from you. I'm rather baffled. I suspect that I did something wrong, but I'm at a loss to know what it is.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Sounds like you accidentally fried it Was the PIC still functioning? If so, you may have driven an I/O line too hard. Or perhaps you set a port as an output temporarily when it was supposed to be an input, resulting in friage. You can fry electronics quite easily by getting the order of your port settings wrong (even simple things like the location of your TRIS instructions could do it). There's lots of other chip functions that can have the same effect if you're not careful. That is kind of a natural consequence of having I/O lines that can serve as both input or output.

Or it could be things like putting 12V in the wrong place, etc...

So many ways to fry them, it's hard to even begin to guess exactly how it happened.

A trouble ticket might be overkill since it's pretty unlikely it's a fault with the PIC.

The odd thing is that both PIC's still work and if I didn't mind their operating at about 45 degrees and was willing to supply them enough 5v to do that they would be fine. As it is the 7805 voltage regulator gets pretty hot when you demand that much amperage out of it.

I got a return on the trouble ticket I submitted to Microchip about the problem with the overheating in the 18F4610 a few hours ago. They said that what had probably happened was that I got out-of-range voltage into the chip and caused what they call "CMOS latchup". In short, out of range voltage, especially negative voltage, can cause the PIC to literally short out.

Here is the essence of what happens...

If power is supplied to a CMOS device such as a memory product or a microcontroller when an ESD event occurs, the device can be triggered into a