At 09:20 AM 4/5/03 -0500, Olin Lathrop wrote:
> > Take VS+:  To charge an capacitor from 0 to 10v or more potential takes
> > more power than charging it to 5v wich would be 10v thanks to the 5v
> > offset if connected as manufacturer reccommends.  Result is longer
> > startup time, but yes it may work.
>
>The real issue is where you want to dump the ripple current.  I prefer to
>keep the supply rail as clean as possible, so I bypass the MAX232A at the
>chip and tie the other end of the +10V capacitor to ground.

Olin - scope it or, better yet, use a current probe and scope.  Connecting
the Vs+ capacitor the way you have said makes for a dirtier supply rail,
not cleaner.

The reason this happens is because the swinging capacitor connects between
Vdd and Vs+ to transfer its charge into the Vs+ capacitor.  This causes a
dip in Vdd if you connect the negative side of the Vs+ capacitor to
ground.  That dip goes away if the negative side of the Vs+ capacitor is
connected to Vdd.

I've tried it both ways and Maxim got it right as documented in their data
sheets.

dwayne

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Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
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