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[SOLVED] Op-amp voltage follower not following input

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countmybones

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Hi, I have a simple op-amp voltage follower using OPA683. When the op-amp is powered by +3.3 V and -3.3 V supplies, the ouput voltage maxed out at ~200 mV when I change the input from 0 V to 1 V.

But when I change the power supply to +5 V and -5 V, the output follows the input.

Any idea why the 3.3 V circuit does not work as intended?

 

alexan_e

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According to your schematics you use +3.3v/-3.3v and +2.5v/-3.5v
I don't see any +5/-5v supply
 

LvW

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Hi, I have a simple op-amp voltage follower using OPA683. When the op-amp is powered by +3.3 V and -3.3 V supplies, the ouput voltage maxed out at ~200 mV when I change the input from 0 V to 1 V.
But when I change the power supply to +5 V and -5 V, the output follows the input.
Any idea why the 3.3 V circuit does not work as intended?

The OPA683 is a current-feedback amplifier - and as such it needs an (optimized) feedback resistor, even in unity gain configuration. See data sheet, Fig. 11.
In your case, the value for Rf should be approx. 600...1E3 ohms.
 

keith1200rs

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According to your schematics you use +3.3v/-3.3v and +2.5v/-3.5v
I don't see any +5/-5v supply

That is just bad labelling. The voltage sources are V2 and V3 and the voltages are both 5 (no dot, so V2 5 and V3 5).

Keith.
 

FvM

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The picture looks like a TINA simulation result, apparently the model isn't representing the device specification. OPA683 is said to work up from +/- 2.5V. LvW is right about the need for Rf, but it shouldn't matter in a DC sweep.
 

countmybones

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The datasheet says power supplies from +/- 2.5 V to +/- 6 V, so I think +/- 3.3 V should work.
These are simulated results using TINA-TI, available free from TI.com.

I reran the simulation placing Rf and also changing V1 to 1 V. The DC sweep for Rf from 0 Ohm to 2k Ohm using +/- 3.3 V supplies does not work either, but changing to +/- 5 V is ok.


The model not representing the device correctly in TINA?
 

countmybones

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Ok, I managed to import the OPA683 spice into LTSpice and it simulates fine at +/- 3.3 V.
 

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