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ESR of ceramic capacitor. How to read the resistance-frequency graph?

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ridgemao1983

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This graph is from murata's capacitor selection tool.

The lowest impedance is 0.003Ohm at 0.9Mhz.
The lowest resistance is 0.002Ohm at 0.2Mhz.

I think I should use the impedance-frequency graph, so the ESR of the capacitor is 0.003Ohm and the resonant frequency is 0.9Mhz.

But what is the meaning of the resistance-frequency graph? If the "resistance" means the real part of the impedance, the resistance shouldn't vary with the frequency.

Both Mutara and TDK capacitors have the graph for resistance-frequencies and impedance-frequencies, what is the meaning of this "resistance"?
 

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If the "resistance" means the real part of the impedance, the resistance shouldn't vary with the frequency.
Only in a over-simplified first order model. If you consider ESR as the real impedance part of a series equivalent circuit, it will be of course frequency dependend:
- because it also represents dielectric losses. By nature of the measurement, they can't be distinuished from true series resistance.
- because series resistance is frequency dependend itself, due to skin effect and proximity effect.
 

The capacitor will resonate with its lead inductance to give a true minimum impedance, at higher frequencies the increasing impedance of the inductance of the leads will lead to a rise in impedance, which will be inductive.
Frank
See forum post by Genomerics wrt ESR of caps
 
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