----- Original Message -----
From: "peter green" <plugwash@P10Link.net>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Thursday, December 07, 2006 10:02 PM
Subject: RE: [PIC] ADC voltage mismatch problem


> > Peter,
> >
> > Why can't the boost be driven off of an IO pin?  Is there a
> > current problem?
> >
> > Vbat
> > -----|>-------|>-------- Vboosted
> >          |          |
> >          =          =
> >          |          |
> > ----------          _ GND
> >  Pic io
> > ON 3.3 V to 5 V
> > OFF 0 V
>
> Yes there is a current problem though not in the sense you might think
>
> the pic is drawing its current from vboosted but the pic is also
essentially trying to supply the current for vboosted.
>
The pic will be up and running under the 3.3V regulator at the time the
boost will turned on.

Is the pic io pin trying to supply current or is it just providing a voltage
reference for the first cap?  I thought that all the current would be
passing in through the first diode and then out through second diode once
the Pic IO line goes from low to high.  Therefore there would be essentially
no current flowing in the PIC io pin.

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