[SI-LIST] Re: Why is capacitor with high ESR
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <weirsp@xxxxxxxxxx>, <Chris.Cheng@xxxxxxxxxxxx>, "'''Si-List ' ' '" <si-list@xxxxxxxxxxxxx>
- Date: Tue, 7 Dec 2004 08:35:34 -0500
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.
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
