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AD8629 slow response

Question asked by TimW Employee on Mar 22, 2011
Latest reply on Apr 6, 2011 by TimW

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



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?