AD829 stability

Hello,

Is the AD829 stable in the following conditions ? What is the Phase Margin ?

- CL=150pF capacitor load

- RL=~1kohms resistor load

- Vs = +/- 5V

- Ccomp = 15pF to inverted input

I attached the schematic (VEE = -5V and VCC = +5V).

Can I simulate the phase margin with PSPICE and how ? Is the model realistic in theses conditions ?

Thanks for your answer,

Mathieu

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  • Hi Mathieu,

    I apologize, in my experiments, I was connecting the compensation capacitor to ground instead of at the inverting input as in your circuit. I just tried out your circuit connections on bench, and I am seeing oscillation at the output. I just heard back from the engineer, and unfortunately, the AD829 is a very old part and its SPICE model cannot be relied on to model stability properly. To be more flexible with your compensation options, would you consider using the shunt configuration? Increasing your gain would also work.

    Could you tell me more about your application? I assume that you are trying to get more slew rate out of your circuit since you are using the current feedback configuration for compensation. If it's not in your list of options to use shunt compensation or to increase your gain, maybe you could provide the requirements for your amplifier so that I could try to find an amplifier that will work for your application.

    Regards,

    Kris

Reply
  • Hi Mathieu,

    I apologize, in my experiments, I was connecting the compensation capacitor to ground instead of at the inverting input as in your circuit. I just tried out your circuit connections on bench, and I am seeing oscillation at the output. I just heard back from the engineer, and unfortunately, the AD829 is a very old part and its SPICE model cannot be relied on to model stability properly. To be more flexible with your compensation options, would you consider using the shunt configuration? Increasing your gain would also work.

    Could you tell me more about your application? I assume that you are trying to get more slew rate out of your circuit since you are using the current feedback configuration for compensation. If it's not in your list of options to use shunt compensation or to increase your gain, maybe you could provide the requirements for your amplifier so that I could try to find an amplifier that will work for your application.

    Regards,

    Kris

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