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-0.7V rail creation for op amp
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snarkysparky:
So i want to use a LMC6482 op amp for a CPU A/D converter input buffer with only a single supply.  The amp will go close to the ground rail but not all the way ( 20mv  or 6 cnts with a 10bit 3.3Vref)  and near ground the sinking ability diminishes which would non linearly slow the settling time to ground.

My idea is to generate a 0.7V negative rail to supply just the op amp.  Plan to use one of the CPU outputs to toggle some kind of switching circuit with a few diodes sprinkled in.  I have an idea involving an inductor and some diodes but I would think you guys have some better ideas.  So let me have em please.

ogden:
You may consider purpose-built negative bias IC like http://www.ti.com/product/LM7705 In case this one does not match your needs, there are many other Switched Capacitor Inverter IC's around.
snarkysparky:
Wow,  whoda thought an IC for EXACTLY what I need.

Thanks all.  I think i will mess with blues solution in spice to see if I can get something to work.
StillTrying:
The LMC6482 can do <20mV while sinking 0.15mA according to the data sheet. Page 10 Fig 8.
David Hess:
Another way to generate roughly -0.5 volt at 10s of microamp is to use a diode or bipolar transistor optocoupler as a single junction photovoltaic generator.  4N25 style optocouplers are suitable and can be had for less than 25 cents each.
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