On Dec. 8, Martin McCormick wrote:
> having more than one ground insures that there will be less
> possibility for crosstalk between signals caused by ground loops.
> If one ground is good, two are better.

Dear Martin:

More is not always better! (Ask the friends of Bill W.)

Seriously, I have had a number of experiences with ground loops, and
they are invariably caused by exactly what you are describing as
desirable. In certain carefully controlled cases where packaging or
other constraints force it, multiple ground current paths can be
tolerated since not having them is worse. This does not apply to
situations where there are functionally separate circuits in the same
chip or package (probably what is happening here.)

The basic rules are: use only a single point ground, use a heavy enough
conductor to keep the current-induced voltages low, and *do* separate
the sensitive stuff from the heavy power stuff.

Since the C62 datasheet is a 20-minute download, I'll just be guessing
that they are separating the high current drivers from the more
sensitive circuitry. You might very well gain an advantage (in
reliability, if nothing else) by keeping them separate out to the power
connector of your cktbd, which should be the "single point" as far as
the board's concerned.

Regards, Kris Murphy
Custom Solutions

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