| Electronics > Projects, Designs, and Technical Stuff |
| -0.7V rail creation for op amp |
| (1/4) > >> |
| 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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