[SI-LIST] Re: Importance of Package Height
- From: "Zabinski, Patrick J." <zabinski.patrick@xxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 18 Mar 2002 06:34:04 -0600
If you read Kemet's statement about ESL, they state they use
a copper-slug of the same dimensions as the cap to "zero" out
a "short". They the calculate the inductance of the slug and
add it back in. The end result is that their values will
be about 600 pH higher than that reported by others (which
matches closely to the values Abe points out).
Another difference I've seen between the inductance
values provided by the two companies is that it looks like
AVX provides one ESL value per package type, irregardless
of capacitance value. In contrast, Kemet reports different
inductance values for the various capacitance values. Considering
the internal physical geometries (layer count, layer thickness, ...)
change to obtain different capacitance values, I tend to
rely more on Kemet's data (and manually remove the 600 pH).
Pat
> Larry Smith Wrote:
>
> > >
> > I'm not sure what assumptions Kemet is making for
> > inductance in their calculator. Their inductance seems way high to
> > me. We have measured a lot of caps from a half dozen vendors and
> > Kemet is no different than any of the others. When mounted
> on a low
> > inductance structure, the Kemet cap will behave as if it is
> > significantly less than 1 nH.
> >
>
> The AVX SpiCap program may output considerably
> smaller ESL for similar capacitor than the kemet Spice
> Simulator. As an example, for the ceramic capacitor we
> recently discussed the AVX answer is 1.0 nH compared to
> kemet's 1.94 nH. Sometimes, use of Kemet software is
> preferable because it can show variations of ESL with
> capacitance values (for fixed package
> size) while the AVX calculator can not.
>
> I think (please correct me if I am wrong) the 1.0 nH by AVX
> and the Kemet's 1.94 nH (and all other ESL results by these two
> programs) apply to un-mounted capacitors. Therefore, based
> on your expected 600 pH for that 100 nF 0805 X7R cap
> both of these manufacturer calculators are providing ESL
> values which are too large/inaccurate in this case.
>
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