[SI-LIST] Re: OT: Overvoltage breakdown on 120 nm silicon?
- From: Russel Hughes <russel.hughes@xxxxxxxxx>
- To: Dimiter Popoff <dp@xxxxxxxxxxx>
- Date: Thu, 17 Feb 2011 17:19:51 +0100
ESD diodes on an input broken down? If you have put too much through them
and they have shorted out it may explain your problem.
Cheers
Russel
On 17 February 2011 16:44, Dimiter Popoff <dp@xxxxxxxxxxx> wrote:
> I am facing an unbelievable reality at the moment.
> A processor which will not boot - although all tests I have
> done to it pass.
>
> I still refuse to believe I can have killed the CPU - but after
> 3 days of tracing of the boot process I seem to run out of
> other explanations (heck, I had to dig through code some of
> which I have written 15+ years ago...).
>
> The CPU (an MPC5200B) appears to work - monitor via UART, even disk
> I/O worked etc. - but it fails some way into the boot process.
> This happened after I fixed the power up sequencing closer to
> the specs :-).
>
> That board had been working for nearly a year before that, had survived
> the development process (lots of programming/debugging and power on/off).
> It had lived through all that with a nice spike on the 1.5V, 2.5V and 3.3V
> upon poweron, perhaps 1 to 5mS over the absolute maximum by perhaps
> 50%. I changed that now - and it won't boot, fails at more or less
> the same place (pulls the wrong return address from the stack if I am
> not tracing ....). This is after a few system calls have returned OK
> already. It looks unbelievable to me to have killed the CPU in such
> a subtle way - but I have not seen many killed ones.
>
> How likely is it that I have killed it? The only news about the
> spikes which I believe to may have killed it is that I now know they
> used to exist...
> Not to speak of the other boards which keep on workingfine :).
>
> I also made the CPU check almost all of the 64M DDRAM, write address
> to location/verify - works, did that with the written address rotated
> 0 to 31 times, also works.... And all that also misaligned,
> also works fine - it is pretty maddening really.
>
> I am simply clueless as to how likely it is to break a gate
> with say 2.5V instead of 1.5? I guess drain/source breakdown won't
> be an issue even if they break for a few mS (not enough energy
> to fry anything)?
>
> Hopefully people with more silicon inside knowledge can
> comment...
>
> Thanks,
> Dimiter
>
> ------------------------------------------------------
> Dimiter Popoff Transgalactic Instruments
>
> http://www.tgi-sci.com
> ------------------------------------------------------
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