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OPA2171 differential input range

Martin Fuchs
Prodigy 40 points

Other Parts Discussed in Thread: OPA2171

Hello!

 

I can't find a "differential input range" in the OPA2171-Datasheet. So I suppose the differential input voltage is not limited as long as the input voltages do not exceed the common-mode input range?

 

Regards,

  Martin Fuchs

  • 0
    TI__Mastermind 44790 points

    Hi Martin,

    There is no "differential input range" in the datasheet, but there is a maximum input current limit of +/- 10mA.

    At the input of most operational amplifiers are clamping diodes between input pins to protect from overdrive conditions. Most operational amplifiers are intended to be operated with both inputs at the same potential using negative feedback. Applying a large differential voltage across input pins (also called "crow-baring" the inputs) can result in very non-linear behavior, clamping, and potentially damaging the device.

    Comparators, on the other hand, are designed to be operated with their inputs at larger differential voltages. Comparators are not operated closed-loop, they typically have faster slew rates, and also are expected to output voltages near the supply rail extremes. It is not recommended to operate an operational amplifier as a comparator. It can be done but you must accept the limited comparator performance and take extra precautions to protect the device.

     

    The "Electrical Overstress" section in the OPA2171 datasheet shows one way to protect the op amp input by limiting the input current with a series resistor.

     

    Hope that helps,

    Chris

  • 0 in reply to Christopher Hall
    Prodigy 40 points

    Hello!

     

    This helps, thank you.

    Of course, in normal operation, the inputs will be at the same potential. But we thought about a circuit for power limiting in a non-inverting amplifier, which would pull the inverting input to V+ (via current-limiting resistor) when overload occurs. This would lead to a big differential input voltage.

    But I don't think that this is a good idea anyway...

     

      Martin Fuchs