Re: [SI-LIST] : Capacitor dielectric type

From: Dennis Schmitz ([email protected])
Date: Wed Dec 06 2000 - 12:54:40 PST

I did find this paper on the web. It goes briefly into the theory of a parallel plate transmission line and ways to change its resonant frequency. The mathematics can get pretty messy with anything other than a regular geometry.

----- Original Message -----
From: Mark Gill
To: 'Michael Nudelman'
Cc: 'Dennis Schmitz' ; si-list
Sent: Wednesday, December 06, 2000 2:10 PM
Subject: RE: [SI-LIST] : Capacitor dielectric type

Hey Mike -

Decoupling the backplane is not required if the boards are correctly filtered/decoupled. None of the systems I have worked on require decaps on the backplane (reliability problem), and none of them have ever exhibited this type of problem. But we do have good filtering/decoupling on the -48 V input to each card. Smart powering (which Joseph mentions) is a slicker approach, and very reasonable when considering switching power systems. But depending on the actual parasitics (inductances, resistances, and capacitances), you certainly can get high frequency ringing upon insertion - try simulating with SPICE to get a feel. The toughest parasitic should be the inductance. There are some ferrites which offer good resistive losses at higher frequencies. I would still call this an inrush phenomenon.

Mark
-----Original Message-----
From: Michael Nudelman [mailto:[email protected]]
Sent: Wednesday, December 06, 2000 12:54 PM
To: Gill, Mark [NCRTP:9030:EXCH]
Cc: 'Dennis Schmitz'; si-list
Subject: Re: [SI-LIST] : Capacitor dielectric type

And, yeah - the backplane should be de-coupled as well. The problem is - to find 48V ceramic SMT caps of significant cacacitance is a pain.
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:[email protected]]
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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