10-30-2018 01:57 PM
We've got a deployed design that uses an XC9572XL CPLD. Its role is essentially a glorified multiplexer / decoder.
All the outputs from the CPLD go through other ICs before they reach the outside world, via level shifters or RS232 converters, except for 2. Those outputs go direct to the outside connector, with no ESD protection or other protection devices. These I/O are unused and undriven.
So far, we have had 2 failures where the CPLD appears to short circuit - it stops working, gets hot and draws lots of current.
Our only suspicion we can think of is that one of those two pins are hit with an ESD event which causes the short circuit that we are seeing. Could their be another explanation? What other failure modes exist in the CPLD?
We're looking at getting an ESD gun to test this more thoroughly, but in the interim, any advice would be appreciated.
11-03-2018 05:05 AM
2 failures out of how many samples? If this is really common (eg. 2/4 boards have failed) then I'd take six off the shelf, cut the tracks to those pins on three of them, and see whether you can replicate the failure. If you can only cause it on the unmodified boards, that's pretty good evidence.
The XC9572XL has 2000V ESD protection, which seems to be normal and should protect it pretty well.
Other things I can think of that might be particularly relevant to this design:
12-04-2018 04:05 AM - edited 12-04-2018 09:07 AM