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OPA2131: How high can the output actually go?

Froylan Aguirre
Prodigy 140 points
Part Number: OPA2131

I am in the process of updating an existing third party design. Part of that process is replacing parts so I have to familiarize myself with the part and their role. The datasheet for the OPA2131 specifies typical output max and min, but no upper bound on either values. However, there is a graph on page 5 titled "Maximum Output Voltage vs Frequency" that implies that this part can output near the rails, but doing so distorts the output signal. Is it accurate to state that the OPA2131 could possibly output higher than the "typical" specs, but doing so introduces distortion?

  • 0
    TI__Mastermind 23490 points

    Hello, 

    The linear operating range for the output swing is specified by the open loop gain conditions for output swing. In the case of the OPA2131 we specify 3V from either rail. Shown below the open loop gain specification is with a +/-15V power supply. 

    Taking the output voltage beyond this linear operating range can start to enter the non-linear operating range which does increase distortion as the output stage transistors start to enter triode. Eventually the output will rail and clipping will occur. The output specification shown below often refers to the non-linear operation of the device and states how close the output can get to either supply rail. This however is a railed out and non-linear condition. The most useful specification for the linear operating region really comes from Aol (open loop gain).

    I hope this explanation is helpful. Let me know if I can be of further assistance. 

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 140 points

    So if the op-amp outputs a signal near or higher than (V+)-2.5, the device has effectively railed out, correct?

  • +1 in reply to Froylan Aguirre
    TI__Mastermind 23490 points

    Hello Froylan, 

    If the output signal goes beyond V+ - 3V it is entering the non-linear range and is at risk of clipping (railing out) is the best way to think about it. 

    Below you can see the output swing vs output current. The output voltage is railed out in these measurements at Iout = 0mA. This is the closest the output voltage can get to the supply rail and is non-linear. 

    To assure linear operation we recommend to keep the output signal within 3V from either supply rail for the conditions highlighted below. 

     

    Best Regards, 

    Chris Featherstone

  • 0 in reply to Chris Featherstone
    Prodigy 140 points

    Thanks for clarifying the output range.