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

WOW, I stand corrected!!  I am sure getting some
educational value out of signing up this list. :-)

It really does feel scary to run signal traces over a
plane where a raging river of electrons is squeezing
its way through. If you can lay thick layers of copper
you can possibly also modulate thickness and try to
route the raging river away from underneath the
sensitive parts. Unless the river is making noise in
totally different frequencies than what you're sending
down the signal lines and you can do some filtering.
Very cool challenge!!

Thanks, Eddy


--- Ken Cantrell <Ken.Cantrell@xxxxxxxxxxxxxxxx>
wrote:
>
> Eddy -
> I agree it seems a little scary, but it just depends
> on what you're used to
> doing.  I run ganged MegaLynx's (Tyco)rated at 30A
> each over 1 oz Cu planes,
> and still keep within the termal requirements using
> standard heat-sinking on
> the FPGAs.  Fans are required.  The board doesn't
> melt, and the noise isn't
> excessive if the board and PDS are designed
> correctly.  I think you get more
> noise injection overdriving your inputs.  But I do
> remember that when I
> first tried it....I had my fingers crossed.
> Ken
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
> Eddy
> Sent: Monday, June 18, 2007 9:37 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: HIGH DC Current on GND Plane
> 
> 
> "Saturation at DC is spelled meltdown"  ROTFLMAO
> 
> 60 Amps is an awful lot. That's like the current
> required to start a good size car! My first thought
> was "that has got be noisy as hell!". Theoretically
> the DC current should not cross-talk anything into
> your signal lines but I have a very hard time
> believing that 60 Amps of current can be quiet
> enough.
> However, I have seen Amps being confused with
> milli-Amps before....  60 Amps is unrealistic to be
> flowing through a PCB. The copper would be curling
> off
> the FR4. There has to be a typo here somewhere....
> 
> Eddy
> 
> --- "Townsend, Fred" <ftownsend@xxxxxxxxxxxx> wrote:
> >
> > I don't know the parties involved here but I think
> I
> > would start
> > analysis with psychoanalysis. It would take a lot
> of
> > convincing for me
> > to buy into this methodology. You don't say if the
> > 60 Amps is 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 board
> > where I would be looking for 4oz copper if your
> > vendor can supply it.
> > Saturation at DC is spelled meltdown. Have you
> done
> > temperature rise
> > analysis?=20
> >
> > The only good news about this design I can see is
> > iron magnetically
> > 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 used=20
> > as reference for multiple of 6.6 Ghz serdes lines
> ,
> > PCI-e lines and GE
> > lines
> > Is there anything similar to 'saturation' in
> > Inductors applicable to GND
> >
> > plane?
> > ( Due to saturation of flux in the flux carrying
> > medium , beyond a=20
> > certain amount of DC current inductors saturate
> and
> > wont act as=20
> > inductors for any AC superimposed on the DC. )
> > Will cross talk 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 current=20
> > mixing in planes ??
> 
> 
> 
> 
>
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