AD8676 Unity Gain Stability

Hi team,

I have a question about the unity gain stability of AD8676. I am not sure if the AD8676 can be used for unity gain configuration. I am currently using it in a configuration similar to the circuit below. 

Simulation Result

For AC Sweep settings I am using logarithmic from 1 to 5 Mhz with 1000 points per decade. It's a bit hard to see on this graph, but the curve starts to behave strangely before 1 Mhz. On the datasheet, it says the wide bandwidth is 10 Mhz typical. In addition, there is a graph of the closed-loop gain where the the curve starts to round off after 10 Mhz. 

This leads me to guess that the AD8676 cannot be used for unity gain applications because it is not stable at unity.

I apologize if my questions seems confusing. I am still a junior at university so my understanding is limited. If you could answer my question it would be greatly appreciated.

Thank you,

Norman Guo

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  • +1
    •  Analog Employees 
    •  Super User 
    on Jun 11, 2021 12:35 AM in reply to NORMGUO

    Hi Norman,

    A macromodel is an "approximation" of the device behavior. It won't be exact.

    Your AD8676 LTspice simulation seems to have stopped at just above 10MHz. If you continue further in frequency, you'd see that after the ~1.8dB peaking predicted by the simulation, the output response does roll-off. 

    Many factors affect peaking including load resistance, layout, load capacitance, supply decoupling. The macromodel may or may not capture all these factors and again it's only a starting point approximation of the device behavior. Bench performance should be performed as the next step.