SNOS674G November 1997 – April 2020 LMC6482
It is quite common to use large values of feedback resistance with amplifiers that have ultra-low input current, like the LMC6482. Large feedback resistors can react with small values of input capacitance due to transducers, photo diodes, and circuits board parasitics to reduce phase margins.
The effect of input capacitance can be compensated for by adding a feedback capacitor. The feedback capacitor (as in Figure 64), Cf, is first estimated by:
which typically provides significant overcompensation.
Printed-circuit-board stray capacitance may be larger or smaller than that of a bread-board, so the actual optimum value for Cf may be different. The values of Cf should be checked on the actual circuit. (Refer to the LMC660 quad CMOS amplifier data sheet for a more detailed discussion.)