[SI-LIST] Re: FW: Re: HIGH DC Current on GND Plane

Wow!  Why 4 ounce power planes?  Must drive your fabricator nuts trying to
etch and laminate such thick copper.

Lee Ritchey


> [Original Message]
> From: Shimko, Steven R. <s.shimko@xxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 6/19/2007 4:39:18 AM
> Subject: [SI-LIST] FW: Re: HIGH DC Current on GND Plane
>
> Eddy-
>
> I am working on a low voltage (1.5V) system that needs to distribute
> over 100 amps of current across 4 backplanes with less then 1% loss.  I
> am not the power system designer, but I have high speed digital signals
> that need to go over those same backplanes, so am familiar with the
> issues.  The most recent configuration for the PWB is a 30+ layer
> stackup with several 4 oz copper layers.  So it can, and is done.  Just
> takes copper!
>
> Steve Shimko
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of steve weir
> Sent: Tuesday, June 19, 2007 1:40 AM
> To: eddyvk@xxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: HIGH DC Current on GND Plane
>
> Eddy, think telecom backplane.  Big iron boxes today support 2-3kW. =20
> With a -48V supply that still adds up to 40-60 amps or even more.
>
> Steve.
>
> Eddy wrote:
> > "Saturation at DC is spelled meltdown"  ROTFLMAO
> >
> > 60 Amps is an awful lot. That's like the current required to start a=20
> > good size car! My first thought was "that has got be noisy as hell!".=20
> > Theoretically the DC current should not cross-talk anything into your=20
> > signal lines but I have a very hard time believing that 60 Amps of=20
> > current can be quiet enough.
> > However, I have seen Amps being confused with milli-Amps before.... =20
> > 60 Amps is unrealistic to be flowing through a PCB. The copper would=20
> > be curling off the FR4. There has to be a typo here somewhere....
> >
> > Eddy
> >
> > --- "Townsend, Fred" <ftownsend@xxxxxxxxxxxx> wrote:
> >  =20
> >> I don't know the parties involved here but I think I would start=20
> >> analysis with psychoanalysis. It would take a lot of convincing for=20
> >> me to buy into this methodology. You don't say if the 60 Amps is=20
> >> static but if it changes there will certainly by cross talk!
> >> Can you say ground
> >> bounce? Normally one would want such current on the outside of the=20
> >> board where I would be looking for 4oz copper if your vendor can=20
> >> supply it.
> >> Saturation at DC is spelled meltdown. Have you done temperature rise=20
> >> analysis?=3D20
> >>
> >> The only good news about this design I can see is iron magnetically=20
> >> saturates. Air and epoxy doesn't.
> >>
> >> Fred Townsend
> >>
> >>
> >> -----Original Message-----
> >> From: si-list-bounce@xxxxxxxxxxxxx
> >> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >> On Behalf Of Joe Paul M
> >> Sent: Saturday, June 16, 2007 3:07 AM
> >> To: si-list
> >> Subject: [SI-LIST] HIGH DC Current on GND Plane
> >>
> >>
> >>
> >> I have a midplane carrying 60Amps of current and Same GND plane is=20
> >> used=3D20 as reference for multiple of 6.6 Ghz serdes lines , PCI-e=20
> >> lines and GE lines Is there anything similar to 'saturation' in=20
> >> Inductors applicable to GND
> >>
> >> plane?
> >> ( Due to saturation of flux in the flux carrying medium , beyond =
> a=3D20
>
> >> certain amount of DC current inductors saturate and wont act as=3D20=20
> >> inductors for any AC superimposed on the DC. ) Will cross talk=20
> >> increase due to the absence of mutual inductance between
> >>
> >> signals and gnd plane ?
> >> Is there anything else that can go wrong due to this DC , AC=20
> >> current=3D20 mixing in planes ??
> >>    =20
> >
> >
> >
> > =20
> >
> ________________________________________________________________________
> ____________
> > Looking for earth-friendly autos?=20
> > Browse Top Cars by "Green Rating" at Yahoo! Autos' Green Center.
> > http://autos.yahoo.com/green_center/
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