[SI-LIST] Re: Decoupling capacitors
- From: Lieby David <DLieby@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 17 May 2002 10:20:39 -0700
I have some experience with problems in RFI. To get some systems to pass FCC
class B with enough margin it is necessary to add low value caps. The best is
setting them at two orders of magnitude in sequence from 10pf to whatever. I
like 10pf, 1nf, 0.1uf, 10uf placed in groups and a couple of extras at the
corners of the board or plane.
They really do make a difference in radiated emissions, whether they help SI or
not
dav0
dlieby@xxxxxxxxxx
dav0@xxxxxxxxxxxxxxxx
"mittalr@xxxxxxxxxx" wrote:
>
>
> On a slightly tangential topic. Have you ever wondered the need for 100pf
> caps. Everyone just seems to sprinkle them as a safety measure but I see no
> need for them because
> - the IC by itself will have about 50-100pF. I checked with many IC guys and
> the ICs where you really need decoupling are generally big enough to have
> that much decoupling on-chip.
> - On top of this you have inter-plane caps.
>
> I have seen many of my designs get away with no 100pF caps. I would use 1nF
> and 0.1uF, rather than 100pf, 10nF and 0.1uF. Anyone have any other
> experience...
>
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