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From: email@example.com (Jeff Walther)
Subject: Re: How to Choose Cap to Filter Pwr for IC?
Organization: Illuminati University
NNTP-Posting-Date: Thu, 19 Sep 2002 19:21:34 CDT
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Date: Fri, 20 Sep 2002 00:21:34 GMT
In article <9osa8kAuyai9Ew4m@jmwa.demon.co.uk>, John Woodgate
> I read in sci.electronics.design that Jeff Walther wrote
> (in ) about 'How to Choose Cap
> to Filter Pwr for IC?', on Thu, 19 Sep 2002:
> >Also, tantalum or ceramic or whichever is less expensive? The boards I've
> >examined seem to use ceramic for the small caps right next to the Vcc pins
> >and one or more larger value tantalum caps as a sort of backup reservoir
> >elsewhere on the board.
> This is generally accepted as good technique. Since your chips are
> fairly fast, you may find 10 nF = 10 000 pF better than 100 nF = 0.1 uF
> for the close-in parts.
It sounds like the 1 uF tantulums I have on hand would not be a good
> > Is this purely a cost issue or is ceramic faster
> >responding than tantulum or something?
> More or less. There are two defects in all capacitors - inductance and
> resistive loss. Inductance slows down the response to a demand for more
> current and resistance limits the current available. Ceramics mostly
> have lower inductance and resistance but until recently values above 1
> uF were not available and even now they are not cheap.
The thing that puzzles me about this is that the ceramic chip capacitors
seem to be less expensive than the tantulums, at least in the Digi-Key
catalog I'm looking at. So I was seeing ceramics actually used on
baords, but getting the impression that the tantulum were better given the
higher cost. But if ceramic are better for this application and cheaper,
that sounds great to me.
Do these appear to be a good choice? (No I won't hold it against anyone
who states an opinion if it turns out badly.)
Thank you to all who responded to my question.
Mike, why did you mention electrolytic caps in your posting? Are
tantulums also electrolytic? I see some that are listed as tantulum
electrolytic but others that are just listed as tantulum.
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