[SI-LIST] Re: Interference from planar magnetics
- From: "Bob Welte" <welte@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 28 Jan 2003 12:59:24 -0500
Thanks for the comments.
So the good news is I will get some magnetic shielding from the copper
shape. But I am concerned about the details:
Assuming that I have 1oZ Cu on the surface, and have a shape (ground)
beneath the VRM, even if the shape thickness is equal to the skin depth of
the switching frequency, that would attenuate the magnetic fields by a
factor of 2.72. How much coupled noise could the remaining fields induce
in my low voltage digital traces below? How big does the shape need to be
(probably depends magnetics characteristics)? Should I tie it to ground
with vias... at what spacing? And what if the switching supply is only
200, or 500 khz?
It would seem that some modeling is in order. How can I model the coupling
from the fields that do penetrate through the copper shape? I would also
need to include some type of model for the VRM. Are there any tools that
anybody can suggest?
Bob Welte
IBM Microelectronics
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