I am using an OP484 and would like to know for good design practice what a good minimum value for capacitance that should be added to the feedback loop is. Any general guidelines or starting points. Thanks
Thank you for your question. It is true that a feedback capacitor is added to an op amp circuit to make it stable. The capacitor value will depend on your feedback resistance Rfb and input capacitance Cin (capacitance from inv input to non-inv input of the op amp). Instability happens because the Cin and Rfb combination creates a zero and that this makes our noise gain increase as frequency increases, until our noise gain intersects with the open loop gain plot. When we add a feedback capacitor, we introduce a pole. This pole rolls-off the noise gain so that it will not intersect with the open loop gain plot. Given this, the feedback capacitor also reduces our bandwidth, which is the trade off for the better stability achieved.
Please let me know if you have further questions.
I hope this helps.
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