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LTC1050 opamp voltage follower saturation problem


I am using an LTC1050 precision opamp. I have applied +-5 V dual rail supply at Vdd and Vss. The output pin 6 is connected to inverted input pin 2. And pin 3 is signal input. So everything is same as an opamp voltage follower should be. 

When I power up the circuit , the output voltage swings to +ve rail and in my other samples of LTC1050, it swings to negative rail when no input is connected to pin 3 and it is left floating.

However when I connect actual voltage input to  pin 3 then it works fine and precise and follows the voltage properly and neatly.

My concern is why does output swings to either +ve or -ve rail with pin 3 left floating ?

My main issue is to interface the output to an ADC to measure both +ve and -ve voltage output but I cannot stress the input pin of ADC to -0.3 to Vdd+0.3V. I have already damaged one ADC module with this. Please suggest if Opamp is working ok and if I need ADC input protection.

  • Hi,

    From your third paragraph, I think the opamp is working properly since you said that it functions properly when there is an input voltage.

    Is there a reason why you need to leave the input of the opamp floating?

    There's a variety of reason why the output swings to the rail when the input is floating. This could be due to noise, interference, or some type of coupling from your setup.

    Since you're using the opamp as an interface to an ADC, you could try supplying the opamp with the same supply for you ADC +/- some tolerance. This way when your opamp saturates, it won't violate the input pin of the ADC.