Hi

LTC2418 is a pretty good delta-sigma ADC. It has two versions which support
I2C and SPI. I used them and they are -really- good. Very high precision,
AFAIR I achieved non-fluctuating 20bit value, didn't try to top. Might  be
worth looking at, my 2 cents.


On Wed, May 1, 2013 at 11:09 PM, Dwayne Reid <dwayner@planet.eon.net> wrote=
:

> Good day to all.
>
> We've just been contacted and asked if we can design an inexpensive
> current source that is computer controlled.  However, the specs are
> considerably higher than anything that I've done in the past.
>
> What they want:
>
> Output current adjustable from 10uA to 1 Amp.  Step decade ranges are
> acceptable - it does not need to be able to be adjustable over a 5
> decade range in one fell swoop.
>
> Output voltage compliance of !! -5V !! to +10V.  I don't know if they
> really want this thing to be capable of a bipolar output but am in
> the process of finding out.  For now, assume that the output
> compliance is single polarity only.
>
> Here's the kicker: accuracy of 0.01% of the set-point.
>
> I don't yet have any idea of frequency response requirements but,
> again, am in the process of finding out.  However, I *think* that
> they are doing battery coulometry, so slow response is probably acceptabl=
e.
>
> The customer wants the units to be computer controlled.  I was just
> going to use some form of USB - Serial arrangement - most likely
> using USB-equipped PICs.  I do plan to isolate the unit from the host
> USB port with some form of isolation barrier.
>
> I do adjustable current sources and sinks with 8 to 10 bit accuracy
> on an irregular basis.  But this is the first time that I've been
> asked to do something approaching 14 bits of accuracy.
>
> Questions:
>
> Is anyone aware of something with similar specs that is already
> readily available?  The customer is currently using a bunch of
> expensive Keithley units and is looking for less expensive
> alternatives.  Personally, I'd rather point the customer to an
> already-existing solution rather than starting this particular design
> cycle.
>
> But: if I do have to design this beast, Does anyone have any favorite
> A/D and D/A convertors that are 14 bit accurate or better?  I don't
> normally use parts that accurate and would prefer to have people whom
> I trust make suggestions rather than just starting to pour over
> data-books and find out that the parts that at first seem to make
> sense are now unobtainium.  SPI preferred, I think, but willing to
> look at anything.
>
> Many thanks!
>
> dwayne
>
> --
> Dwayne Reid   <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> (780) 489-3199 voice          (780) 487-6397 fax
> www.trinity-electronics.com
> Custom Electronics Design and Manufacturing
>
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