[SI-LIST] Re: Why is capacitor with high ESR
- From: steve weir <weirsp@xxxxxxxxxx>
- To: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>, <Chris.Cheng@xxxxxxxxxxxx>, "'''Si-List ' ' '" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 07 Dec 2004 05:54:40 -0800
Istvan, thanks.
Regards,
Steve
At 08:35 AM 12/7/2004 -0500, Istvan NOVAK wrote:
>Steve, Chris ans All,
>
>Sorry for the long silence, I was out of the office not reading e-mail.
>
>I agree witrh Chris that we should not try to fix a problem that
>does not exist. So as long as we can convince ourselves that we
>do not excite the structural resonances, they do not matter and
>we dont need to do anything about them.
>
>In cases, however, when there is evidence that the structural
>resonances will be excited by the system, either the excitation
>has to be changed, or the resonances dampaned/removed, or
>other measures have to be put in place to cope with the situation.
>
>In such cases, when you convince yourself that the solution should
>be to suppress structural resonances, DET does help. If the ESR
>you need is in the ohms range, as Arpad indicated in his question,
>it has been proven that discrete small-size external resistors do help.
>
>Another point was that probably the components on a real board
>would change and/or suppress the resonances without any extra
>component or effort. While this unquestionably may happen, we
>cannot count on it as granted. When I measure the designs I made
>during the past years by removing the dissipative termination
>components from real boards, significant worsening can be seen.
>
>As the required resistance value gets lower, the extra inductance
>from an external resistor piece gradually swamps out the benefits
>of resistive damping, and this is where one-piece ceramic parts with
>known (and higher than usual) ESR would help.
>
>I also have to agree with Steve and others who say that increasing the
>ESR of MLCCs is not a trivial task, especially that the entire industry
>has been asking for lower and lower ESR for decades: reversing a
>long-lasting trend is not easy and it takes time. On the other hand,
>several component manufacturers already work on this problem to
>create ceramic and other capacitors with increased and controlled
>ESR. The information that could be made public appeared in several
>papers; the ones that I was involved in can be accessed at
>http://home.att.net/~istvan.novak/papers.html These publications
>indicate the vendors which are the most active in the area.
>
>Best regards,
>Istvan Novak
>SUN Microsystems
>
>----- Original Message -----
>From: "steve weir" <weirsp@xxxxxxxxxx>
>To: <Chris.Cheng@xxxxxxxxxxxx>; "'''Si-List ' ' '" <si-list@xxxxxxxxxxxxx>
>Sent: Monday, December 06, 2004 8:55 PM
>Subject: [SI-LIST] Re: Why is capacitor with high ESR
>
>
> > Chris, it seems that we have good agreement on almost all points but
> > somehow seem to still disagree! In the present environment, I feel that
> > DET is not something that is economically practical. So my interest in
> > discussing it is only for the technical performance. In that context it
> > really doesn't matter that there are quite effective means for realizing
> > systems that pass emissions and perform reliably. they don't take away
> > from DET and DET doesn't take away from them, because I don't see it
> > getting deployed.
> >
> > I agree that there is nothing one can do on the PCB to correct a bad IC
> > package(s).
> >
> > I agree that misreferencing is a common problem, and DET does not address
> > that, nor should one try.
> >
> > Two wrongs may not make a right but three do! ( I felt I had to throw
>that
> > in. )
> >
> > I don't advocate small caps either, unless there is a very specific
> > frequency that a tuned filter can address. Using small capacitors in the
> > same case size that supports larger values just increases the number of
> > parts and cost.
> >
> > However, a point at which we diverge seems to be how much noise escapes
>the
> > board due to repeated reflections impinging vias and escaping through
> > features / components on the board exterior.
> >
> > Regards,
> >
> >
> > Steve.
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