[sdiy] Single supply use of the SSM2164

[Neil Johnson]

Hi Olivier,

> I am working on a +9V (battery or wallwart) powered gadget using a SSM2164.

Hmm.... you're getting _very_ close to the minimum specified +8V supply 
there, very marginal indeed.

> In the example given in the "Single supply" section of the datasheet,
> the mid-rail is obtained through a resistor network + buffer, but I am
> concerned that this might not entirely eliminate voltage variations
> that might be present in the +9V rail. Would using a voltage reference
> work here?

You need to be careful about what happens to the rails when the supply 
is coming up or going down.  The SSM2164 has a rather nasty failure mode 
when the -ve rail is less than 0.7V below the GND pin.  More details here:

http://www.milton.arachsys.com/nj71/index.php?menu=2&submenu=2&subsubmenu=3

 > What I would like to understand is if there is any
> fundamental difference between a SSM2164 and an op-amp when it comes
> to single supply use

Absolutely!!  Most op-amps are two-rail devices (+ve and -ve) -- any 
ground connection is just as an input.  Even for so-called single-rail 
op-amps like the infamous LM324 which sits between +Ve and GND, but now 
what you think as GND is actually the -ve rail, just with a different name.

The SSM2164 is a three-rail device requiring a proper ground rail and 
two power rails.

 > - anything that would make the recommendations
> given for op-amps here
> http://www.ieee.li/pdf/essay/single_supply_op_amp_design.pdf
> irrelevant.

No that's a reasonable paper.  Good ideas on producing a stable bias 
voltage.  But for an SSM2164 I'd stick with the datasheet circuit unless 
its performance is below what you need.

Cheers,
Neil
-- 
www.njohnson.co.uk