[SI-LIST] Re: Bypass Capacitor Selection

All,

Please note that the correct link is: http://www=2Espeedingedge=2Ecom/ (Th=
ere
is a typo error in the URL provided by Lee)=2E

Elya

Original Message:
-----------------
From: Lee Ritchey leeritchey@earthlink=2Enet
Date: Tue, 30 Dec 2003 10:06:45 -0800
To: si-list@enclustra=2Ecom, si-list@freelists=2Eorg
Subject: [SI-LIST] Re: Bypass Capacitor Selection


Martin,

You have two questions in your message=2E  First, package size and second
capacitor value=2E

Package size first:  The motivation for small package size is lowest
possible parasitic inductance=2E  One must include mounting inductance as
part of this=2E  When this is added, the difference between the total
inductance of an 0402 and 0603 is so small that 0603 is a better choice, a=
s
it makes assembly easier=2E

Capacitor value:  Usually, the objective is to achieve a low impedance
across a very broad range of frequencies=2E  Using a single value capacito=
r
will not achieve this=2E  There are several papers that address this and g=
ive
insight into how to determine the values and quantities of capacitors=2E  =
If
you send me a separate e mail I can supply some of them=2E  One of them is=
 on
my web site  www=2Espeedingdge=2Ecom=2E

Lee


> [Original Message]
> From: SI List <si-list@enclustra=2Ecom>
> To: <si-list@freelists=2Eorg>
> Date: 12/30/2003 5:23:45 AM
> Subject: [SI-LIST] Bypass Capacitor Selection
>
> Dear All,
>
> After studying many books, the bottom line for high frequency bypass
> capacitor selection seems to be the following:
>
> Use the smallest possible package and then take the largest valued
> capacitor available in that package=2E
>
> Although 0201 capacitors are available, they are kind of hard to
> assemble=2E So in our design, we are thinking of using 0402 X5R parts=2E=

>
> In a 0402 package, the largest value available seems to be 1 uF=2E
>
> My frequency range of interest is DC to 500 MHz=2E In addition to the
> bypass capacitors, I know that there must be a pair of closely spaced
> VCC/GND reference planes=2E
>
> My questions:
> 1=2E Does it make sense to only use 1 uF 0402 capacitors for bypassing?
> Other people often use a combination of 1 nF/10nF/100nF=2E 2=2E I have b=
een
> looking at the frequency characteristic of 100 nF 0402 X5R capacitors
> given in the data sheets of different manufacturers=2E The impedance vs=2E=

> frequency plot often looks quite different from manufacturer to
> manufacturer=2E Should I choose the manufacturer with the best frequency=

> characteristic or are all such parts almost equivalent? 3=2E Does it mak=
e
> sense to use surface mount capacitor arrays for bypassing?
>
> Thanks for all your expert feedback=2E
>
> Best regards,
>   Martin Heimlicher, heimlicher__at__enclustra//dot//com
>
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