RE: [SI-LIST] : Chassis Ground to Digital Ground

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From: Chris Robertson (Chris.Robertson@gets-1000.com)
Date: Tue Apr 24 2001 - 11:22:06 PDT


Gerald,
I've gotten some experience with this subject.
There are some prerequsites to considering where to tie your ground(s).
        Will your mounting holes provide an adequate path and meet current
requirements?

        Do you need to use the board in some fashion that it may need to be
disconnected from the chassis?

        Will the chassis ground path provide a quiet enough connection and not
intoduce any noise nor will it have any potential between the path and the
actual chassis?

        Does it need to be or is the chassis ground tied to the primary ground?

On your initial or protype grounds you may want to use several jumpers to
connect the digital ground to the chassis ground for testing options. (I say
several, because inadequate connections at that voltage/current levels are
capable of producing areas of potential on your goround plane.) Use star
grounds as opposed to daisy chain grounds.

If possible you may want to make a plane layer for your digital ground
(removed from below any area that may produce excessive
noise)and cover the unused area on the outter layer with the chassis
copper/plane. Use several vias in strategic areas to provide adequate ground
connection as well as connecing the chassis mounting (screw hole) by way of
the hole wall plating.

HTH
Chris Robertson
Chris.Robertson@Gets-1000.com <mailto:Chris.Robertson@Gets-1000.com>

Senior Designer
Lockheed-Martin Services Inc.
4912 Research Dr.
Huntsville, AL 35805
(256) 722-2626

All:

I am currently designing a power supply that operates from a -48V feed. It
was recommended that the top layer (of a 4 layer board) be connected to
chassis ground. The connection will be made by having all mounting holes
connect to chassis ground through mounting screws.

My question is: How do I connect the digital ground to frame ground?

Thanks
Gerald

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