RE: [SI-LIST] : Capacitor dielectric type

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From: Ken Cantrell (Ken.Cantrell@srccomp.com)
Date: Tue Dec 05 2000 - 12:09:04 PST


Lee,
What do you recommend for those situations? Sounds like the worst of both
worlds. You either ring like crazy, or you heat the system up and make a
lot of (thermal) noise.
Ken
-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Ritchey Lee
Sent: Tuesday, December 05, 2000 12:36 PM
To: Charles Grasso
Cc: Bob Weber; Larry Miller; si-list
Subject: Re: [SI-LIST] : Capacitor dielectric type

Unless you have delata Is in the 10 Amp and up as occur with large, fast
processors, I agree as well.
Lee

Charles Grasso wrote:

    Somewhere in all this didn't someone agree with Dr Johnstone who I
beliveadvises lots of cheap (i.e lossy) caps for decoupling??
    ----- Original Message -----
    From: Bob Weber
    To: Larry Miller ; si-list
    Sent: Tuesday, November 21, 2000 6:50 AM
    Subject: RE: [SI-LIST] : Capacitor dielectric type
     The bypass cap ESR improves damping (smoothing the impedance peaks &
valleys) in the 50 to 250MHz range. The degree of improvement varies
depending on capacitance values (bypass and plane capacitance).I select the
caps (voltage, dielectric, and package size) to make sure I get enough ESR
to be effective in damping. Obviously, small packages are good (small ESL).
I avoid capacitors that result in a "thick stack" (i.e. a many layered MLC
cap). The extra layers give more capacitance, reduce the L (a small effect),
and drive down the ESR. Cap sizes that need fewer layers will in general
have the most ESR.Using the AVX SpiCap software,
http://www.avxcorp.com/SpiApps/spicap/ , compare the ESL and ESR of a X7R
cap at 1, 10, 47, and 100nF (100nF will have to be a 16V cap). As the
capacitance goes down, the ESR goes up. This makes sense when you view the
cap as a stack of smaller value layers. The total capacitance is increased,
but the ESR is reduced. A 100nF X7R cap is a block, while the 1nF is a
sliver. Z5U can be selected to give more ESR in a 100nF cap (fewer layers
and the dielectric is more lossy).Bob W.
      -----Original Message-----
      From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Larry Miller
      Sent: Monday, November 20, 2000 11:57 AM
      To: Bob Weber; Tae-Kwang Jeon; si-list
      Subject: RE: [SI-LIST] : Capacitor dielectric type
      Interesting point. R-C "snubber" networks have long been used to each
transient ringups in power transistor and SCR circuits at lower frequencies.
      What frequency range would you be considering this for?

      Larry Miller

        -----Original Message-----
        From: Bob Weber [SMTP:rweber@txc.com]
        Sent: Monday, November 20, 2000 6:11 AM
        To: Tae-Kwang Jeon; si-list
        Subject: RE: [SI-LIST] : Capacitor dielectric type
        TK,

        This will likely cause some discussion, but I avoid using NP0 or C0G
        capacitors for bypassing because of their low ESR. Small value (1nF)
X7R
        capacitors have noticeable ESR (0.5ohm), but this is a good thing.
It
        provides a damping element to absorb the ringing that develops on
the
        power-ground planes due to parasitic resonances between the bypass
        capacitors and the unavoidable inductance of the connections.

        Bob W.

        -----Original Message-----
        From: owner-si-list@silab.eng.sun.com
        [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Tae-Kwang Jeon
        Sent: Thursday, November 16, 2000 6:47 PM
        To: si-list@silab.eng.sun.com
        Subject: [SI-LIST] : Capacitor dielectric type

        Hello,

        I'm trying to put multiple decoupling capacitos on my board mixing
small and
        large values in order to minimize the ESL and ESR.
        What I'm wondering is when I use different types of dielectic for
the
        capacitors. For instance, I'm going to use 0.022uF X7R type and
470pF of
        NPO type because NPO has the lowest ESR.

        Does anybody know whether or not it's not a big deal in terms of
mixed
        dielectric material for high frequency decoupling?

        Thanks,
        TK

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