On Thu, 21 Feb 2002, Dave Dilatush wrote:

> Spehro Pefhany wrote...
>
> >What would the consequences be of going to 20K on the midrange 10-bit A/D
> >input? I've read the reference manual and the data sheet. If the input is
> >bypassed with a 0.1uF or something of that ilk, it seems to be primarily
> >limited by the worst case leakage current on the input vs. guaranteed
> >accuracy. I'm willing to lose 1 bit or 1.5 bits in the A/D, and high
> >temperature operation is not required.
> >
> >Any thoughts on this?
> >
> >I'd normally put an op-amp in there without much thought, but the quantities
> >are such that thought will be well rewarded if a few cents can be snipped.
>
> The only other error I can see you getting, other than the drop across
> your 20K resistor due to input leakage, would be a scale factor error
> that can occur if you have the input bypassed and are sampling it at a
> high rate.  But if you're not looking for full 10-bit accuracy I can't
> see this as a big issue.
>
  You need also  ( according to datasheet ) to increase also the minimum
required aquisition time. It's possible ( not tested yet ) to keep the
full 10 bit accuracy. The leakage current from datasheet is +/-500nA.
I think is a mistake or an absolute maximum rating.
Vasile

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