pic18f4520 problem

[misel0019]

Hello everyone,

I'm again with my problem.
Now I am working with pic18f4520.

I am using that ic for controlling generator.

I have power supply 48volt to 12volt by using ic3844 (smps) then 7805 regulator.

Problem:
Now the problem with my uc is that it shorts internally automatically.

Means I installed the product and it runs fine after some days when i go to the site I get my product with empty display.
And while I want to program that ic again.
I got my ic short internally.
My programmer can't recognise that ic.

I have installed that product in 50 sites and got problem in 15 sites, others having no problem.

Same program ?s the cause I can't understand...
Can anyone help me????

_misel00019

[misel0019]

I forgot to mention some of behavior while I was coding that program.

I normally use smart prox5 to burn ic.

Behavior: I take one New ic from bar and working with it.
I change program and write it on that ic.

After rewriting that ic several times i get one or two pin does not behave normal.

Means one or two pin goes low or high permanently.

That pin does not change.
I can say thats my programming problem but when I change that ic with same hex file that is normal.

Completing that program whole, I found 5 or 6 ic that are damaged in two or three pin (pins are either high or low internally).

Waiting for your reply.
My coordinator are losing faith on 18f4520...
Please help me.........

_misel

[yerpa]

I don't know what a "smart prox5" programmer is, but it sounds like it might be wrecking your chips. I have programmed the 18F parts many hundreds of times (using Microchip's PICSTART Plus or PICkit3 programmers) without any failures.

More likely, your circuit may be getting a high voltage spike that damages the chip. You may need more power supply filtering and a zener diode to clamp the voltage to five volts DC.

[Ttelmah]

I'd have to say if it is happening after some time, then it is almost certainly being caused by electrical noise spiking the chip, rather than by the programmer.
I'd do a simple 'flash an LED' test, using low power components only, and try writing this to a chip fifty times. If it still works OK, you have largely ruled out the programmer.

You talk about significant power being present. Things that 'classically' can kill an IC like this, are the release 'flyback' energy release from an inductor, if not properly clamped. The path back to the gate of a fet, or base of a transistor usually breaks down first as the voltage rises, routine the energy straight back into the IC driving this, or spikes induced on input lines to the chip as signals switch.
I'd be looking at some tiny difference on the 'good' versus 'bad' sites, like a wire to the processor routed in a different position.

Best Wishes