unfortunatly splitting the board or any other dramatical change of the design is out of the question. i think that the problem is sudden changes of the required current that is not propertly handled by the decoupling capacitors / power supply. the board was never build to be servisable (filled with lots of fine pitch BGAs with no much room around for rework) the board should fit itu a predesigned case, so i cannot change the size eather.
Declan Moriarty wrote: >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!" > > > > -- Author: Michael Gefen INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
