Re: [SI-LIST] : Capacitor dielectric type

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From: Ritchey Lee (leeritchey@earthlink.net)
Date: Wed Dec 06 2000 - 08:07:32 PST


Don't worry about heating up the system f rom this loss. I use the
lossiest dielectric I can get. Turns out that this is the cheapest
capacitor as well.

Lee

Ken Cantrell wrote:

> 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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>

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