LMC6482_16 Datasheet, PDF (23/39 Pages) Texas Instruments – LMC6482 CMOS Dual Rail-to-Rail Input and Output Operational Amplifier

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LMC6482
SNOS674E – NOVEMBER 1997 – REVISED APRIL 2015
Typical Applications (continued)
8.2.1.2.1.1 Capacitive Load Tolerance
The LMC6482 can typically directly drive a 100-pF load with V_S = 15 V at unity gain without oscillating. The unity
gain follower is the most sensitive configuration. Direct capacitive loading reduces the phase margin of op-amps.
The combination of the output impedance of the op-amp and the capacitive load induces phase lag. This results
in either an underdamped pulse response or oscillation.
Improved frequency response is achieved by indirectly driving capacitive loads, as shown in Figure 62.
Compensated to handle a 330pF capacitive load.
Figure 62. LMC6482 Noninverting Amplifier
R1 and C1 serve to counteract the loss of phase margin by feeding forward the high-frequency component of the
output signal back to the amplifiers inverting input, thereby preserving phase margin in the overall feedback loop.
The values of R1 and C1 are experimentally determined for the desired pulse response. The resulting pulse
response is shown in Figure 63.
Figure 63. Pulse Response of
Lmc6482 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. Large feedback resistors can react with small values of input capacitance due to transducers,
photo diodes, and circuits board parasitics to reduce phase margins.
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