VIN

VOUT

+

VOUT

RISO

CL

Vcc

14

LPV821

SNOSD36A – AUGUST 2017 – REVISED DECEMBER 2017

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Device Functional Modes (continued)

8.4.2 Driving Capacitive Load

The LPV821 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 output impedance of the amplifier

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

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

peaking, the op amp might start oscillating.

Figure 38. Resistive Isolation of Capacitive Load

Table 1. Capacitive Loads vs. Needed Isolation Resistors

0 – 20 pF

not needed

50 pF

160 k

Ω

100 pF

140 k

Ω

500 pF

54.9 k

Ω

1 nF

33 k

Ω

5 nF

15 k

Ω

10 nF

5.62 k

Ω

Figure 39. Typical Step Response