Re: Virtex4 DCM doesn't work unless freezing cold

msn444@xxxxxxxxx wrote:
Hi everyone,

We've been shipping a Virtex4 FX20 based product for a few months now
with relatively few problems. However, we're seeing a 60+% failure
rate in our latest batch of boards, characterized by the V4 DCMs not
locking or providing any output at all unless the chip is freezing
cold. Neither the design, board house or CM shop has changed at all
from our previous working batch, which generally runs pretty hot
(~60C) with no known problems.

The details I have found are: when powering up from room temperature,
other logic implemented in the chip seems to work, but the DCMs have
no output and are not locked. If I give the FPGA a good shot of cold
spray and power up the device, it becomes fully functional, until the
temperature rises somewhat and the DCM ceases completely. Among the
samples I've tried, the temperature at which it stops working ranges
from really cold to slightly below room temperature.

The clock source is a 25MHz crystal oscillator -- I tried a function
generator and nothing changes. I tried twiddling VCCAux as I've seen
suggested and no difference there, either. Has anyone seen such a
dramatic DCM failure before, or have any ideas what might be causing
this?

Thanks,
Mike.

Hi Mike,
It probably isn't NBTI.
http://www.xilinx.com/support/documentation/white_papers/wp224.pdf
Google :- nbti group:comp.arch.fpga
But, a bake at 150C for 48 hours would prove that it isn't!

You also might liek to read this thread from a few days back about reset.
Google :- "Virtex 4 DCM problem" group:comp.arch.fpga

Good luck, Syms.




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