+

-

VIN

RISO

VOUT

CL

14

LPV811, LPV812

SNOSD33B – NOVEMBER 2016 – REVISED NOVEMBER 2016

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Device Functional Modes (continued)

7.4.4 Driving Capacitive Load

The LPV81x is internally compensated for stable unity gain operation, with a 8 kHz typical gain bandwidth.

However, the unity gain follower is the most sensitive configuration to capacitive load. The combination of a

capacitive load placed directly on the output of an amplifier along with the amplifier’s output impedance creates a

phase lag, which reduces the phase margin of the amplifier. If the phase margin is significantly reduced, the

response will be under damped which causes peaking in the transfer and, when there is too much peaking, the

op amp might start oscillating.

In order to drive heavy (>50pF) capacitive loads, an isolation resistor, RISO, should be used, as shown in

Figure 45. By using this isolation resistor, the capacitive load is isolated from the amplifier’s output. The larger

the value of RISO, the more stable the amplifier will be. If the value of RISO is sufficiently large, the feedback loop

will be stable, independent of the value of CL. However, larger values of RISO result in reduced output swing and

reduced output current drive. The recommended value for RISO is 30-50kΩ.

Figure 45. Resistive Isolation Of Capacitive Load