[SI-LIST] Re: HIGH DC Current on GND Plane
- From: "Nick Langston, Sr." <Nick.Langston@xxxxxxxxxxxxxxx>
- To: <kgrhoads@xxxxxxxxxxxx>, <joepaulm@xxxxxxxxx>
- Date: Tue, 19 Jun 2007 10:34:43 -0700
Hey Kevin, that is an interesting point. We are often testing parts
with that much Current and more in automated handlers. While the device
is being tested, within 10cm we have devices being positioned for the
next test or whatever. There are things that happen in Vdd with these
kind of 60A parts running at 5Gb/s + that we always blame on decoupling
and board thickness. I think your point is worth a look.
Nick
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Kevin G. Rhoads
Sent: Tuesday, June 19, 2007 9:50 AM
To: joepaulm@xxxxxxxxx
Cc: si-list
Subject: [SI-LIST] Re: HIGH DC Current on GND Plane
>I have a midplane carrying 60Amps of current
> ...
>Is there anything else that can go wrong due to this DC , AC current=20
>mixing in planes ??
Most of the issues have already been addressed. However, there is one
case which can crop up here that has not been raised, so I will comment
on that.
1) V =3D d/dt(LI) normally L is constant, so only dI/dt is considered.
But with 60 amps you have a lot of I and large H,B fields can result.
2) at this point MOTIONAL effects are no longer trivially ignorable
as negligible. THey may not matter, but you can't dismiss them out
of hand. That is because motion can change the effective L (or M for
mutual inductance) and with large I small dL/dt can still give large
voltages. V=3D d(LI)/dt =3D L dI/dt + I dL/dt You need to get a
handle on dL/dt, which leads to:
3) what size is the board? Will it experience vibration? Any moving
parts nearby? If yes to vibration or motion -- how near? how fast?
Are the things moving conductors? (like cable bundles flapping in
the breeze or vibrating or flex couplings or ...)
HTH
Kevin
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