AD822
Figure 46 shows a method for extending capacitance load drive
capability for a unity gain follower. With these component
values, the circuit drives ꢀ000 pF with a ±0% overshoot.
20mV
. . . . . . . .
2µs
. . . .
. . . . . . . . . . . . . . . .
. . . . . . . . . . . .
100
90
+V
S
0.01µF
8
+
1/2
100Ω
V
IN
AD822
V
OUT
–
0.01µF
20pF
C
10
4
L
. . . . . . . .
. . . .
. . . . . . . . . . . .
. . . . . . . . . . . . . . . .
0%
–V
S
20kΩ
Figure 44. Small Signal Response of AD822 as
Unity Gain Follower Driving 350 pF
Figure 46. Extending Unity Gain Follower Capacitive Load Capability
Beyond 350 pF
Figure 4ꢀ is a plot of capacitive load that results in a 20° phase
margin vs. noise gain for the AD822. Noise gain is the inverse of
the feedback attenuation factor provided by the feedback
network in use.
5
4
3
2
1
300
1k
3k
10k
30k
CAPACITIVE LOAD FOR 20° PHASE MARGIN (pF)
C
L
R
F
R1
Figure 45. Capacitive Load Tolerance vs. Noise Gain
Rev. G | Page 21 of 28
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