Recently, Somebody Somewhere wrote these words
> hi, about the current stuff: there are several FPGAs that do quite the
> same job, so i'll talk about one of them. 1. the power supply changes
> can be observed also on the supply outputs. 2. the FPGAs are powered
> by 1.5V and 3.3V each supply pin is connected to the power iland (as
> mentioned before) and to a ceramic capacitor of 100nf or 22pf (the
> value taken from someone elses observation). the FPGAs are BGA parts
> (BG896) so the power connection uses VIA and the capacitor connect
> directly to VIA on the other side of PCB. 3. the current reqired is
> about 2A (peak) from each power source.
>
I would take on board people's comments and do the rest of the work. You
say 300-400mV drop on the power line. Keep going. Check in many places
along the power line. Does the voltage drop along the positive? Connect
more points directly to the psu o/p. I have a sure feeling you are not
supplying enough current, and if the 300-400mV is visible there it will
confirm it.
Take heed of what you are doing. This may be propped up in the lab, but
techies will meet it in the field when the least thing goes wrong and it
causes mayhem. Buying a new board (Last resort) may not solve the
problems, and in that case you will have major trouble on your hands.
What you are building is unserviceable in the extreme.
Can you increase the power output? Increase the voltage? Stagger the
activity of the FPGAs? Split the unit into a sandwich (2 boards)? 18
layers is ridicolous, btw. It sounds as if you should take the advice of
Fagan from Oliver Twist (The film, not the book)
"I think I'd better think it out again!"
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
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