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OpAmp high capacitive load drive simulation

Category: Software
Product Number: AD8605
Software Version: LTSPICE 17.0.34

I've simulated this ez simulation:

It states that driving high capacitive load can be possible with single small resistor in between load and opamp? Is it right?

Also how this can be like this: In simulation, higher cap i.e 5uf needs lower series resistor 2.2 but lower capacitance i.e. 0.5uf needs higher resistance to stablize 10 ohm. This is contrast of what has been formed in my mind: higher cap need higher resistor. This is conflict could someone also explain this conflict?



added question extenstioon
[edited by: mohammadsdtmnd at 6:29 AM (GMT -4) on 9 Jul 2022]

Top Replies

    •  Analog Employees 
    •  Super User 
    Jul 9, 2022 +1 verified

    Hi ,

    In this particular case, you don't need the 0.5ohm series resistor on the output as LTspice simulation of AD8605 with 10uF cap load shows that it's stable (except some ringing) without…

    •  Analog Employees 
    •  Super User 
    Jul 9, 2022 in reply to Hooman +1 verified

    Hi ,

    I'm sorry. I misspoke earlier. I showed simulations with 1000pF (not 10uF) above.

    Yes, I see that LTspice predicts that with 10uF cap load, adding 0.5ohm series output resistance…

Parents Reply
  • Hi ,

    I'm sorry. I misspoke earlier. I showed simulations with 1000pF (not 10uF) above.

    Yes, I see that LTspice predicts that with 10uF cap load, adding 0.5ohm series output resistance gets rid of the tiny ringing at the output as shown below:

    Simulation file here:

    AD8605 cap load EZ 7_9_22.asc

    I'd say that this is possibly because with no series output isolation resistor, you are on the edge of instability and not fully unstable. Therefore, the 0.5ohm isolation must be enough to get rid of the tiny ringing after output transition. Most likely, you'd need to verify the results on the bench and not just rely on simulation alone.

    Regards,

    Hooman

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