AD8629 slow response

When using an AD8629 in a circuit (see attachment) for in loop capacitive load compensation, the devices shows a very slow response to get within a few uV of the final value.  On the order of seconds.

The values for the circuit would be:

CL = 0.4uF

Rf=Rg=4k

Rx=200

Rl ~ 10k

Cf = 1200pF

Vin @ Rg is the output of a DAC typically between 0 and 400mV

Vin @ IN+ is a 200mV dc level.

Power supplies are +/- 2.5 volts.

I've run a quick simulation at my end, and I'm getting the proper response within a few milliseconds, which is on the order of what I would expect.  I also realize that the 1200pF is probably too small for the proper compensation.

Is there anything else going on inside these auto zero amplifiers that would present difficulties in a circuit such as this?

Thanks,

Tim

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