[SI-LIST] : ESR and bypass caps

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From: Doug Brooks (doug@eskimo.com)
Date: Thu Feb 03 2000 - 15:38:06 PST


Hi all,

We have been putting some thought into this question and have derived,
definitively we believe, some "truths" about this topic. They are
summarized below. The first two or three are apparent and not really news,
although we "prove" it from the normal formulas. The fourth has been
verified as a "truth". We have presented all this in an article "ESR and
Bypass Capacitor Self Resonant Behavior: How to Select Bypass Caps. We
invite you to review the article.

1. As ESR goes down, the troughs get deeper and the peaks get higher!
2. The minimum impedance value is NOT NECESSARILY ESR (or ESR/n); it can
and is lower than that!
3. The minimum impedance points are not necessarily at the capacitor
self-resonant points.
4. For a given number of capacitors, better results can be obtained from
more capacitor values, with moderate ESRs, spread over a range than with a
smaller set of capacitor VALUES, with very low ESRs, even at well chosen
specific self resonant frequencies.

In order to verify the theory, we had to write a program that could, for
any arbitrary set of capacitor (and inductance and ESR) values, find the
minimum and maximum frequencies and impedance values. We have done that.
The calculator is available for license.

The article can be obtained from our web site:

http://www.ultracad.com

Follow the links to the ESR article.

Doug Brooks
UltraCAD

.
************************************************************
See our updated message re in-house seminars on our web page
.
Doug Brooks, President doug@eskimo.com
UltraCAD Design, Inc. http://www.ultracad.com

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