UltraCAD Design, Inc


ESR and Bypass Cap Self-Resonant Behavior


We have looked closely at the theory behind bypass capacitor self resonant behavior and have published some conclusions in our landmark paper in 2000 entitled "ESR and Bypass Cap Self-Resonant Behavior, How to Select Bypass Caps." These conclusions include:

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, where n is the number of identical parallel capacitors); it can be lower than that!

3. The impedance minimums are not necessarily at the self resonant points of the bypass capacitors.

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 with a smaller set of capacitor values, with very low ESRs, at even well-chosen specific self resonant frequencies.

The theoretical calculations for the impedance response of a large number of parallel RLC circuits of different values can be quite complex. We wrote our own program to help with this.

A description and mini-operator's manual for the program (in *.pdf form) is available here. 

The calculator program itself is described here.

For information regarding a license for the full version of the program, look here.


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