LMC662CMX Datasheet, PDF (8/23 Pages) Texas Instruments – LMC662 CMOS Dual Operational Amplifier

LMC662
SNOSC51C – APRIL 1998 – REVISED MARCH 2013
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However, if the feedback pole is less than approximately 6 to 10 times the “ideal” −3 dB frequency, a feedback
capacitor, C_F, should be connected between the output and the inverting input of the op amp. This condition can
also be stated in terms of the amplifier's low-frequency noise gain: To maintain stability, a feedback capacitor will
probably be needed if:
(2)
where:
(3)
is the amplifier's low-frequency noise gain and GBW is the amplifier's gain bandwidth product. An amplifier's low-
frequency noise gain is represented by the formula:
(4)
regardless of whether the amplifier is being used in an inverting or non-inverting mode. Note that a feedback
capacitor is more likely to be needed when the noise gain is low and/or the feedback resistor is large.
If the above condition is met (indicating a feedback capacitor will probably be needed), and the noise gain is
large enough that:
(5)
the following value of feedback capacitor is recommended:
(6)
If
(7)
the feedback capacitor should be:
(8)
Note that these capacitor values are usually significantly smaller than those given by the older, more
conservative formula:
(9)
C_S consists of the amplifier's input capacitance plus any stray capacitance from the circuit board and socket. C_F
compensates for the pole caused by C_S and the feedback resistor.
Figure 16. General Operational Amplifier Circuit
8
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