RE: [SI-LIST] : Re: Backplane Board insertion problem

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From: Mark Gill (gillmf@nortelnetworks.com)
Date: Wed Dec 06 2000 - 09:33:42 PST


Recall that the planes still represent a capacitance (instant short
circuit), and with essentially no impedance to reduce the inrush of current,
plugging in the board is the same as attaching a small uncharged cap
directly to the backplane - a glitch. There are a number of approaches...a
simple one you can try is to place an inductor (simulate effects of size
first) in series with the power feeds. Be sure to add a diode in parallel
with the inductor so that when you withdraw the card, a large L di/dt does
not appear on the backplane (the diode becomes forward biased).

Mark

-----Original Message-----
From: Dennis Schmitz [mailto:den@positron.net]
Sent: Wednesday, December 06, 2000 11:31 AM
To: Mendelsohn, Joseph P (Joseph); si-list
Subject: [SI-LIST] : Re: Backplane Board insertion problem

We removed all components from the power section of the board, except for
the fuses. We suspect that the capacitance of the power planes on the board
itself pings the backplane causing the resonant response.

----- Original Message -----
From: "Mendelsohn, Joseph P (Joseph)" <jmendelsohn@lucent.com>
To: "si-list" <si-list@silab.eng.sun.com>
Cc: "'Dennis Schmitz'" <den@positron.net>
Sent: Wednesday, December 06, 2000 11:14 AM
Subject: Backplane Board insertion problem

> I would tend to agree with Mark. You probably do not have enough
> capacitance in the backplane, or you do not have an inrush(soft-start)
> circuit. There are many ways to avoid this problem. Check out the
> following brief in EDN
> http://www.ednmag.com/ednmag/reg/1997/121897/26di_07.htm
> <http://www.ednmag.com/ednmag/reg/1997/121897/26di_07.htm> . This type of
> circuit or, a simple MOSFET with a set RC time constant can help.
>
> Joseph
>
> -----Original Message-----
> From: Mark Gill [mailto:gillmf@nortelnetworks.com]
> Sent: Wednesday, December 06, 2000 9:22 AM
> To: 'Dennis Schmitz'; si-list
> Subject: RE: [SI-LIST] : Capacitor dielectric type
>
>
> 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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