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OPA192 Output Impedance

EE_MT
Intellectual 390 points
Other Parts Discussed in Thread: OPA192

I'm interested in using the OPA192. My input signal is a square wave, 0V to 2.5V, with a width/duration of 0.1ms to 10ms. The OPA192 will be configured so that it outputs a constant current output (load will be in parallel with the feedback resistor).

My question is, the OPA192 has a high output impedance - about 400 ohms in the range that I will be operating in. Does the OpAmp compensate for the high output impedance internally, or do I have to take the voltage drop into account? Example: 36V Vs rail, output resistance is 1000 ohms, the OPA192 output 30V, but only deliver 21V ? And if the OPA192 doesn't compensate for the voltage drop, is the output voltage range really only -500mV from the positive rail?

Also, there is a graph for Vout (V-) vs Iout, but not for Vout (V+) vs Iout. Why is that? Is there data for Vout (V+) vs Iout? 

Thank you.

  • 0
    TI__Guru* 93105 points

    Hello EE_Matt,

    Figure 31, shown on OPA192 data sheet page 18,  is a graph of the open-loop output impedance (Zo) vs frequency. Zo is primarily 400 ohms resistive over much of the frequency range. The closed loop output impedance (Zout), will be much, much lower than Zo. The Zout value will be equal to Zo, divided by the loop gain, at the frequency of interest; where the loop gain is the difference between the open-loop gain (Aol) and the closed-loop gain (Acl). If the Acl is kept to reasonable levels the Zout will be fractions of an ohm, or ohms, depending on the Aol at the specific frequency.

    The output swing range of the OPA192 primarily will be a function of its ability to swing while delivering output current. Data sheet Figure 20, Output Voltage Swing vs Output Current (Maximum Supply), provides that information. I am not sure why only the negative voltage/current capability was given in the graph, but the positive and negative output capabilities are usually quite similar for most op amps. Note that most of the OPA192 Electrical Characteristics are specified with RL equal to 10 k-ohms, or 2 k-ohms, so in most applications it isn't providing a lot of current.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0
    TI__Guru 71516 points
    Matt,
    Did this resolve any questions you had about the OPA192? Are you using it in your design?
    ~Leonard