Models of decoupling capacitors

Regards, Dana.

@danadakk, I am not sure if I would get the model parameters I am looking for. Do you know if the link you provided can also find ESL, ESR for capacitors in different SMD packages ? I have attached a datasheet. How can I find ESR and ESL of that capacitor ?

Hi,

If you consider the model to be a
* capacitor
* a stray L in series
* and an R (ESR) in series.

Then you have: F_res = 1/ ( 2 x Pi x sqrt(L x C))
C is given, f_res from the chart is about 200MHz.
So you can solve the equation.

Also at resonance (frequency) there is no impedance, pure ohmic resistance = ESR.
So if you wanr ESR then just read the chart for ESR at f_res

****

For sure there are more complex models, then finding out the values is more complicated

Edit: corrected formula (green)

Klaus

This means that ESR is the lowest value at the f_res in the impedance plot.
The ESL has to be found using f_res = 1/sqrt(L x C), where f_res is the resonant frequent, C is known and then we can find the value of L which is ESL. This means that we can't find the ESL directly from the inductance graph, right ?

Hi,

First: I made a mistake in my previous post:
f_res = 1/ ( 2 x Pi x Sqrt(L x C)).
(I missed to show the green part. I´ll try to correct this in the other post)

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joniengr said:

This means that ESR is the lowest value at the f_res in the impedance plot.

Click to expand...

As said, it depends on the model you use. The lowest value in the impedance plot is a measure of all dissipated power. So if you have HF loss in the dielectric (or else where) then there is a difference between ESR and the lowest graph value.

joniengr said:

This means that we can't find the ESL directly from the inductance graph, right ?

Click to expand...

Yes, try. And compare the values.

***
Graphs:
Now I did recognize that there is an ESR graph. Here one can see that the ESR @ f_res is lower than the impedance, which makes sense because of the existance of other losses.
What´s unclear to me, why the ESR should be in the region of 200 Ohms at 1kHz.
Not that this matters much - it still is more than 2 decades below the impedance. But I did not expect this.

Klaus

Btw: did you try the "K-SIM" link in the datasheet?

L from inductance graph and fres should give similar results. Did you notice that Kemet K-SIM tool also generates SPICE models?

ESR and ESL in Capacitors :



Regards, Dana.