RE: [SI-LIST] : Capacitor dielectric type

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From: Mark Gill ([email protected])
Date: Wed Dec 06 2000 - 11:10:18 PST

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.

-----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.


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] <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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