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THS4140 output drive capability

volkan serter
Prodigy 80 points
Other Parts Discussed in Thread: THS4140, THS4541

I simulate THS4140 on TINA simulator, Vs=+-12V . Input signal 2Vpp, 1KHz, Sine. Load 150 ohm. Gain=9, Rf/Rg=9. It seems I can obtain 18Vpp output without any problem. But In the datasheet, Figure 17, it seems  for Vs=+-15V and for 150 ohm load output voltage is around +-6V.

So, which one should I take as the correct voltage swing for 150 ohm?

  • 0
    TI__Genius 14015 points

    Hi Volcan,

    I was able to recreate the Figure 17 graph in Tina using Vs=+/-15V, Rf=1k, G=2 and 15VDC across the inputs. It looks pretty similar to the datasheet:

    The voltage swing available at the output depends on your load as well as your Rf value. As Rf is increased, there is less current going through the feedback path, which leaves more current available to go into the load. This creates a higher voltage swing at the output.

    What is your Rf value? 

    Jason

  • 0 in reply to Jason Blackman
    TI__Expert 4950 points

    Volcan,

    The output of the THS4541 is fully differential, so 18Vpp only requires 9Vpp from each output or ±4.5 around the common-mode voltage.  As Jason showed, this is consistent with both the model and the datasheet.

    Xavier

  • 0 in reply to Xavier Ramus
    Prodigy 80 points

    I tried with 15V dc connected across inputs and obtained the same figure. I think I am confused because of  taking peak to peak output voltage as the difference of output voltages shown in the datasheet, which are +6V for Vout+ and -6V for Vout-. So I thought Peak to Peak voltage would be 12 V.

    But for a sinus type output, 18 Vpp, voltage to be generated has to be 9V across 150 ohm load with respect to ground for the peak of the voltage swing. And from the diagram for 150 ohm load the THS4140 can generate 9V across 150 ohm. Correct me if I am wrong.

    I think a graph should be added showing single ended output voltage swing vs load resistance.

    By the way the feedback resistance is 9k.

    Thank you

    Regards Volkan