Re: [SI-LIST] : What's your favourite Screwy SI Concept?

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From: Larry Smith (ldsmith@lisboa.eng.sun.com)
Date: Wed Jan 05 2000 - 09:25:53 PST


> Andrew Phillips wrote:
> > I would be interested to hear other people's favourite 'Screwy SI
> > Concept' - why its screwy and why you think it has hung around in the
> > literature confusing everybody.
>
> I nominate "Extremely low series resistance is important in a bypass
> capacitor."
>
> Once you launch a transient into a power distribution system, it
> has to be dissipated by something. A little series resistance
> can be a good thing.

Whooaa... I'll take issue with that one. If you give me a set of high
frequency X7R and NPO ceramic capacitors with half of the ESR, I will
build you a power distribution system with half of the number of
decoupling capacitors. The number of capacitors required is inversly
proportional to the ESR.

One of our typical products might have 200 decoupling capacitors on one
power rail in order to provide clean transient power up to several
hundred MHz to 70 watt processors. I can cut that number to 100 if I
have capacitors with half the ESR. That saves precious board area,
wiring congestion and cost.

Sorry, I cannot second that nomination. In fact, I am doing everything
I can to convince capacitor vendors to offer low ESR ceramic
capcitors.

regards,
Larry Smith
Sun Microsystems

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