[SI-LIST] Re: Decoupling capacitors
- From: "Joe Paul M" <joepaul@xxxxxxxxxxx>
- To: "steve weir" <weirsi@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 16 May 2005 21:42:32 +0530
Thanks steve.
So I conclude that , I can use 1 uF 0603 caps for all my decap
requirements as it comes at same and practically slightly lower cost
than , 0.1,0.01,0.001 mixture , due to the volume business deals.
-----Original Message-----
From: steve weir [mailto:weirsi@xxxxxxxxxx]=20
Sent: Monday, May 16, 2005 9:23 PM
To: Joe Paul M; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Decoupling capacitors
Joe "capacitors by the decade" can be used properly to theoretically=20
slightly reduce the number of capacitors or increase the ESR of the=20
network. In many common cases, it is just a rote practice that provides
no=20
actual value. Life with SMT devices is much different today than when
we=20
had leaded devices and those practices were first adopted.
Steve.
At 08:42 PM 5/16/2005 +0530, Joe Paul M wrote:
>Thanks Steve,
>
>Your explanations were really good and I did understand your
>explanation.
>
>But I have seen people using, 0.01 uF and 0.001 uF, even when 0.1 uF
>caps for the required voltage rating are available in same package.
>
>Is there reasoning behind the above approach?
>(I have not yet checked the ESL and ESR of these in their datasheets)
>But I understand that typically ESL remains same for same package &
>Dielectric, and ESR reduces with increase in Cap values( as per SICap3
>tool of AVX)
>
>Thanks
>Joe Paul
>
>
>-----Original Message-----
>From: steve weir [mailto:weirsi@xxxxxxxxxx]
>Sent: Monday, May 16, 2005 7:10 PM
>To: Joe Paul M; si-list@xxxxxxxxxxxxx
>Subject: Re: [SI-LIST] Decoupling capacitors
>
>Joe Paul, the ESL may be the same but the ESR of the 1uF in the same
>chemistry and voltage will definitely be about 35-40% that of the
>0.1uF. It is very unlikely that 0.1uF will provide any cost or
>performance
>advantage over 1uF in the same 0603 case from the same mfg at a low
>voltage
>rating. Due to cover layer considerations, depending on the voltage
and
>
>chemistry, the 1uF may actually exhibit lower mounted inductance than
>the 0.1uF
>
>At 2ns/ 160MHz, both capacitors are fully inductive and cover layer
>issues
>aside will have very similar performance. The 1.0uF capacitor has the
>benefit of more capacitance which generally makes it easier to
stabilize
>
>the transition from the bulk capacitors / VRM. Fans of the big "V"
like
>
>Dr. Johnson, Istvan Novak, and myself will usually advise that at the
>same:
>cost, package size and chemistry, take the bigger capacitor. If you
>want
>to find out why some people do things differently, take a look at Larry
>Smith and company's papers on multipole capacitor networks. If nothing
>else, those papers should help you better understand what you are doing
>whether or not you elect to follow the methods they describe.
>
>If you really want to see how your capacitors perform and have access
to
>a
>VNA, I suggest building a test board. You can get details on such a
>board
>from Istvan's papers on his web site, or from mine on the X2Y web
>site. You can put together a decent set of CPW test fixtures for under
>$200. cash and some time. Your biggest expense will be a pair of SMA
>connectors per fixture.
>
>If you want more information on bypass network design, Istvan's web
>site,
>the Teraspeed web site, and the X2Y web site all have papers on the
>subject.
>
>
>Steve.
>At 04:58 PM 5/16/2005 +0530, Joe Paul M wrote:
>
> >I have a doubt regarding decoupling capacitors.
> >
> >I have the option for using 1 uf9AVX 06036D105KAT2A) or 0.1uF
(AVX
> >0603ZC104KAT2A) at same cost.
> >
> >Concerned rise time is about 2nS.
> >
> >Is there any issue in using 1uF caps, if it has same ESR and ESL and
> >package (0603) as 0.1uF.
> >
> >Thanks all
> >Joe Paul
> >
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