AD8529, about open-loop gain model

Hello, everyone

I'm currently designing a non-inverting amplifier circuit with AD8529. Its gain is 2 and it will drive a capacitive load. I want to aquire the open-loop model of AD8529 in order to estimate its transient response and to design appropriate compensation. I refered to the method of testing loop gain T in the book 'design with operational amplifiers and analog integrated circuits', Franco,S., 3rd edition, chapter 8. When simulating, I took off the inverting capacitor and capacitive load, so beta=0.5 and there was no zeros and poles in beta, and I considered T/beta as open-loop gain. Please refer to the attachment to see the simulation circuits and results.

Q1: When powered with +5V/-5V, the simulated open-loop gain curve is same as that of datasheet; When powered with +12V/0V, which is the real working condition, the simulated open-loop gain curve is absolutely different with that of datasheet; How to explain this? Will it be ok to take the simulated open-loop model powered by +5V/-5V as the 'real' model of AD8529, and design compensation with it?

Q2: Is the testing method right? Will it be ok to take 'Vout/(Vp-Vn)' as open-loop gain and test it? Is there any testing circuit recommanded by ADI?

Best regards

circuitsandresults.docx
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  • 0
    •  Analog Employees 
    on Nov 24, 2014 5:21 PM

    Hi Xueliang,

    Our Spice Models are modeled to work at dual supplies, this means that most of our test bench circuits are configured to test for dual supplies. Technically, the response of 12 V supply should be the same for + 5V supply voltage. You could use + 5V open-loop gain response to design compensation for 12 V.

    Regards.

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  • 0
    •  Analog Employees 
    on Nov 24, 2014 5:21 PM

    Hi Xueliang,

    Our Spice Models are modeled to work at dual supplies, this means that most of our test bench circuits are configured to test for dual supplies. Technically, the response of 12 V supply should be the same for + 5V supply voltage. You could use + 5V open-loop gain response to design compensation for 12 V.

    Regards.

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