Re: [SI-LIST] : Capacitor dielectric type

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Wed Dec 06 2000 - 09:52:13 PST


Mark.

I work together with Dennis.

The problem is not inrush. The inrush itself is well-controlled. That
is, you can consider what happens as inrush, when you plug a board with
100pF capacitance into 48V carrying backplane, there is a inrush
current, but it shows as short burst of 80MHz ringing.

I formalized the situation down to a 48V source and couple of thick
wires and a cap of 20-100pF as a load. The ringing is still there.

We do not use pre-charge resistors. It's a thought to use them, we did
in the past and for some reason stopped. I think it was a mistake.

By using a pre-charge, say - 10K, you will charge a capacitance qickly.
The only thin about it - you need another staged pin to do it. Well...we
already staged some; why not stage another one?

Mike.

Mark Gill wrote:

> Dennis -Your board insertion problem sounds more like an in-rush
> current problem than power plane resonance. Do you have further
> details which would confirm resonance over inrush?Mark
>
> -----Original Message-----
> From: Dennis Schmitz [mailto:den@positron.net]
> Sent: Tuesday, December 05, 2000 5:38 PM
> To: si-list
> Subject: Re: [SI-LIST] : Capacitor dielectric type
>
> Can some kind person please point me to some references on
> power-plane resonance? I am researching for a new backplane
> design of an existing system where we are having some
> problems with board insertion causing disturbances on the
> power distribution planes. Thanks in advance.
>

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