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AD8529, about open-loop gain model

Question asked by wangxueliang@ciomp.ac.cn on Nov 20, 2014
Latest reply on Dec 22, 2014 by ScottH

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

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