LMC6482-MIL Datasheet, PDF (22/31 Pages) Texas Instruments – CMOS Dual Rail-to-Rail Input and Output Operational Amplifier

LMC6482-MIL
SNOSD61 – JUNE 2017
Typical Applications (continued)
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Figure 63. Pulse Response of
LMC6482-MIL Circuit in Figure 62
8.2.1.2.1.2 Compensating for Input Capacitance
It is quite common to use large values of feedback resistance with amplifiers that have ultralow input current, like
the LMC6482-MIL. Large feedback resistors can react with small values of input capacitance due to transducers,
photo diodes, and circuits board parasitics to reduce phase margins.
Figure 64. Canceling the Effect of Input Capacitance
The effect of input capacitance can be compensated for by adding a feedback capacitor. The feedback capacitor
(as in Figure 64), 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 bread-board, 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.)
8.2.1.2.1.3 Offset Voltage Adjustment
Offset voltage adjustment circuits are illustrated in Figure 65 and Figure 66. Large value resistances and
potentiometers are used to reduce power consumption while providing typically ±2.5 mV of adjustment range,
referred to the input, for both configurations with V_S = ±5 V.
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