> I use a sigma-delta A/D converter with a differential input for this
> purpose.
> The MCP3551 works well. With a 5V reference and assuming you can get arou=
nd
> 20 bits of data, the per-LSB voltage is 5V / 2^20 =3D 4.77uV
> So with a 10 ohm resistor your lowest increment is about 477nA. In practi=
ce
> it will be pretty difficult to trust all of those bits, but you have plen=
ty
> left over.

I suggested Sigma-Delta as an option, [having had too much (bad)
experience with software versions]. With IC based versions the
manufacturer (presumably) has sorted out the interesting things that
can happen.

Main issue with the MCP3551 is conversion time  a bit over 70 mS or
say 14 conversions per second.
That easily exceeds his "several per second" OK and falls short of the
100 per second 'great".
At 20 bits the tradeoff is acceptable.

MCP3553 is 17 milliseconds woth no price difference.

MCP3551 is notional 22 bits while MCP3553 is 20 bits and (much) more
than adequate.


    Russell

    http://ww1.microchip.com/downloads/en/DeviceDoc/21950e.pdf
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