Re: decoupling caps placement
- From: Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@xxxxxxxxxxx>
- Date: Sun, 21 Dec 2008 18:03:45 -0500
tempus fugit wrote:
Hey all;In our day we call them by pass cap's and as far as i'm concerned,
I've got a circuit that uses 3 4049 inverters. On this IC, the V+ is on pin
8 and the ground is on pin 1. I know that the decoupling caps need to be as
close to the IC as possible, but how can I connect 1 end of the cap to V+
and the other to ground when the pins are so far away? Is it sufficient to
connect 1 end of the cap to V+ and the other to a nearby ground node, or
should the cap be connected close to the actual ground pin of the IC? Also,
do I use 1 cap for each IC? If so, (the ICs are fairly close together)
wouldn't the IC "see" the caps as being the paralleled value of the 3 caps,
thus reducing the available capacitance? I was going to use 0.1uF for the
value of each decoupling cap. Would it also be wise to use a larger (1uF or
higher) cap in parallel?
Thanks
they still are.
As on your question. I've found that the by pass cap really helps
in removing load variations from a previous path from another component
that may also be taxing the rail and causing unstable voltages. Placing
by pass caps between the components as you go along normally cures it.
Unless you're trying to work with high freq R.F. design, I don't
think having a little lead way isn't going to hurt any.
1 uf or more for load swing variations and ~ .01 non inductive type for R.F. issues.
Many times, you'll see a combination of 2 types in a single location.
http://webpages.charter.net/jamie_5";
.
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