[SI-LIST] Re: ESR of caps
- From: steve weir <weirsi@xxxxxxxxxx>
- To: chundi srikanth <chundis@xxxxxxxxx>
- Date: Thu, 08 Oct 2009 23:41:04 -0700
At all frequencies the first approximation of the network impedance is
the inverse of the parallel complex admittance. Parallel ESRs by
themselves are completely inadequate as a means to determine network
response.. The first approximation works up to frequencies where the
series interconnect impedance between the components becomes significant.
At frequencies well above the SRF of the highest SRF component in the
bypass network, the aggregate ESR will appear to be the parallel value,
and the aggrate ESL will be the parallel value. The network impedance
will be dominated at those frequencies by the parallel ESL. Knowing the
ESR is helpful primarily when estimating the severity of resonance with
higher frequency elements such as in-package caps, on die caps, and/or
power cavities.
Steve.
chundi srikanth wrote:
> Hi All
> I need help to understand calculating the equivalent ESR of capacitors in
> parallel. For example if we have tant capacitor with 65mOhm ESR and a
> ceramic cap with 10mOhm ESR, whether the equivalent ESR is simply the
> parallel of these two ESRs? If it is so simple then we can always keep one
> ceramic and tantalums in parallel to achieve low ESR as ceramic always will
> have low ESR?
>
>
> Thank you,
> Sree
>
>
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