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OPA170: OPA170 negative voltage

Sv
Intellectual 500 points
Part Number: OPA170

Hello Team,
Can someone clarify the doubts I am having about the thread mentioned here.
This thread was regarding whether a single supply op amp (OPA170) with +5V at V+ is properly able to convert a -2.5V at its inverting terminal to a positive voltage (the op amp is configured as an inverting amplifier).


The common mode input voltage of the op amp OPA170 is from (V-)-0.1V to (V+)-2V. That is since the V- pin is connected to GND and V+ is connected to 5V, the input voltage range should be within -0.1V to 3V.
Please correct me if I am wrong.


By applying a -2.5V at the inverting terminal, the CM voltage range is violated and the circuit wont work.






That is since the V- pin is connected to GND and V+ is connected to 5V, the input voltage range should be within -0.1V to 3V.
It means the input voltage at the inverting or non inverting terminals of the op amp must be within -0.1V to 3V.
Please correct me if I am wrong.


  • 0
    Guru 302890 points

    Your are correctly describing the voltage ranges.

    In this inverting circuit, if the circuit's input voltage (RSSI) is −2.5 V, and if the opamp output is +2.5 V, then the voltage at the inverting input is 0 V, and everything is OK.

    But if the opamp's output is not yet at the correct value (which might happen when the circuit powers up, or when the input quickly changes), then it can happen that the voltage at the inverting input is below −0.1 V.