[SI-LIST] Re: CPLD getting blown on board

  • From: Donald Nelson <dhwn@xxxxxxx>
  • To: cygnul@xxxxxxxxx
  • Date: Fri, 07 Jun 2013 13:37:57 +0000 (GMT)

Hi Sam, A few items to check:
1) Check the power rails as they ramp up to their correct voltages; do they 
overshoot? Do they settle within the DC specifications of the CPLD? Do they 
have ripple that exceeds spec (checked continuously from powerup to full load)?

2) Are there power sequencing requirements for the CPLD (or other parts) that 
are not being met? (have you verified on a scope that 3.3V is first, followed 
by 2.5V?)

3) Is the CPLD receiving data inputs from other devices before its own rails 
have ramped up (can forward bias the input protection diodes)

4) Are all signals terminated properly?

5) Are all signal voltage levels correct for the I/O banks? 5V signal into a 
2.5V I/O bank on the CPLD, for instance.

6) Have the power supplies been properly qualified for loop stability? Do 
they strongly overshoot during step-increases in load?

7) Is your CPLD pinout correct? For instance, is an output accidentally 
connected to an output from another device?

8) In fact, check your CPLD pinout again: are all of the power pins connected 
properly to the correct rails?

9) Have you verified all of your Gozintas and your Gozoutas for the CPLD? All 
what you expect? ("Gozinta" = "Goes Into", "Gozouta" = "Goes Out of" for you 
younger guys :-)

Good Luck,
-Don
Alcatel-Lucent

--
Don Nelson

"The whole problem with the world is that fools and fanatics are so sure of 
themselves, and wiser people so full of doubt" --Bertrand Russell


On Jun 07, 2013, at 08:49 AM, Scott McMorrow <scott@xxxxxxxxxxxxx> wrote:

> Sam
> Look for excessive overshoot/undershoot on the signal lines received by the
> CPLD.
>
> regards,
>
> Scott
>
>
> On Fri, Jun 7, 2013 at 8:38 AM, Sam Pete <cygnul@xxxxxxxxx> wrote:
>
> > Hi Friends,
> > I am working on a medical board which has multi-core CPU along with other
> > peripherals.
> > we are getting into some issue that CPLD is getting blown out during power
> > cycle or sometimes during reset.
> > out of 210 boards we produced, we have 3 boards exhibiting this issue. The
> > FA report from CPLD vendor says electrical over-stress...
> > The board is not having any hotswap peripherals.... CPLD has 2.5V and 3.3V
> > banks, 3.3V Core/IO supply comes up first then 2.5V.
> > We have gone thru all sorts of checks, negative tests etc., to reproduce
> > this issue and we were unsuccessful....
> > Does anybody faced similar issues earlier? Appreciate if you can provide
> > some clues...
> >
> > thanks
> > Sam
> >
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> -- 
>
> Scott McMorrow
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