LMC7101BIM5 Datasheet, PDF (20/28 Pages) Texas Instruments – LMC7101/LMC7101Q Tiny Low Power Operational Amplifier with Rail-to-Rail Input and Output

LMC7101, LMC7101Q
SNOS719F – SEPTEMBER 1999 – REVISED MARCH 2013
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Figure 65. Resistive Isolation
of a 330 pF Capacitive Load
COMPENSATING FOR INPUT CAPACITANCE WHEN USING LARGE VALUE FEEDBACK
RESISTORS
When using very large value feedback resistors, (usually > 500 kΩ) the large feed back resistance can react with
the input capacitance due to transducers, photo diodes, and circuit 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 66), C_f is first estimated by:
(1)
or
R₁ C_IN ≤ R₂ C_f
(2)
which typically provides significant overcompensation.
Printed circuit board stray capacitance may be larger or smaller than that of a breadboard, so the actual optimum
value for C_F may be different. The values of C_F should be checked on the actual circuit. (Refer to the LMC660
quad CMOS amplifier data sheet for a more detailed discussion.)
Figure 66. Cancelling the Effect of Input Capacitance
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