LMC6484AIMXSLASHNOPB.B datasheet(23/50 Pages) TI2

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7.2.1.2.2 Capacitive Load Tolerance

The LMC648x can typically directly drive a 100pF load with VS = 15V 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.

Figure 7-10 shows how improved frequency response is achieved by indirectly driving capacitive loads.

–

LMC648x

VIN

VOUT

C1 = 100pF

R1 = 300

CL = 330pF

10k

NOTE: Compensated to handle a 330pF capacitive load.

Figure 7-10. LMC648x 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. Figure 7-11 shows the

resulting pulse response.

Figure 7-11. Pulse Response of LMC6482 Circuit in Figure 7-10

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LMC6482

LMC6484

SNOS674J – OCTOBER 1997 – REVISED SEPTEMBER 2024

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