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 mbart,

    I apologize for the delay in response. I've forwarded your query to the engineer who worked on the SPICE model for AD829 regarding simulations to get the phase margin for your circuit. However, I had a spare board here and I tried out your circuit using just one of your branches as input (tried the one with the lowest gain). With a 15pF compensation cap, there is oscillation at the output (see below).

    I switched the compensation cap to 68pF (which is recommended in the datasheet for a gain of 1), and I lost the oscillation. On bench, even with the resistors set to have a gain of 0.5, the output is still stable (see below).

    If you can still make amends to your circuit, I would recommend that you go instead with a compensation cap of 68pF. The only other option would be to increase your gain to get rid of the oscillation.

    I hope this helps!

    All the best,

    Kris

Reply
  • Hi mbart,

    I apologize for the delay in response. I've forwarded your query to the engineer who worked on the SPICE model for AD829 regarding simulations to get the phase margin for your circuit. However, I had a spare board here and I tried out your circuit using just one of your branches as input (tried the one with the lowest gain). With a 15pF compensation cap, there is oscillation at the output (see below).

    I switched the compensation cap to 68pF (which is recommended in the datasheet for a gain of 1), and I lost the oscillation. On bench, even with the resistors set to have a gain of 0.5, the output is still stable (see below).

    If you can still make amends to your circuit, I would recommend that you go instead with a compensation cap of 68pF. The only other option would be to increase your gain to get rid of the oscillation.

    I hope this helps!

    All the best,

    Kris

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