[SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator
- From: "Vishram Pandit" <vishrampandit@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 11 Aug 2003 22:21:05 +0000
I agree with Ray. I have found in my designs that the EMI is very much
dependent on the decoupling capacitor placement. Typically I can place the
decoupling capacitors with the PDS analysis. Also, I can find
experimentally,the hot-spots and place the capacitors. With simulations and
with measurements, I have found that the decoupling capacitor placement is
very critical. It may be in a particular section of the board, it may be at
the bottom (for double sided boards) .... it all depends on the nature of
theproblem.
Thanks,
Vishram
>From: Ray Anderson >Reply-To: si-list@xxxxxxxxxxxxx >To:
si-list@xxxxxxxxxxxxx >Subject: [SI-LIST] Re: UltraCAD ESR and Bypass
Capacitor Caculator >Date: Mon, 11 Aug 2003 09:36:25 -0700 >>>>Lee Ritchey
wrote: >>If the location of decoupling capacitors matters, perhaps some
technical >>demonstration would prove that. Short of such a demonstration,
this is >>speculation and not the sort of thing that should be used to make
design >>choices. >>>>It's time to do some good engineering on this subject
and do away with >>opinion. The UMR paper is good engineering. Anyone who
chooses to >>disagree with it has the burden of showing where it is wrong by
using some >>good science. >>>>Lee >>>>Lee Ritchey
>>leeritchey@xxxxxxxxxxxxx>>Why Wait? Move to EarthLink. >>>Or conversely,
show that it doesn't matter. >>Take a large system board (say about 24"
square) put a bunch of high current >processors and ASICS on the left side
ofthe board. Put all your decaps >on the right side of the board (since you
maintain position doesn't matter). >>In this hypothetical case I can just
about guarantee the board won't function >properly or pass EMI. Admittedly,
it is a contrived case, but I think it >illustrates the point. >>As far as
the technical demonstration goes, we have indeed demonstrated to >ourselves
that position does matter. >>I'm not attempting to further an argument, but
Ido feel those who have >responded with viewpoints other than yours
shouldn'tbe chastised and accused >of spreading unfounded opinion. Don't
discount the chance that an opinion that >differs from yours just might be
correct. >>-Ray Anderson >Sun Microsystems Inc.
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