Datasheet
Data Sheet ADA4830-1/ADA4830-2
Rev. C | Page 17 of 22
DRIVING CAPACITIVE LOADS
The ADA4830-1 and ADA4830-2 are capable of driving large
capacitive loads while maintaining its rated performance.
Several performance curves vs. capacitive load are shown in
Figure 12 and Figure 25. Capacitive loads interact with an op amp’s
output impedance to create an extra delay in the feedback path.
This reduces circuit stability and can cause unwanted ringing
and oscillation.
The capacitive load drive of the ADA4830-1and ADA4830-2 can
be increased by adding a low valued resistor, R
S
, in series with the
capacitive load. Figure 35 shows the test circuit.
ADA4830-1
+
–
C
L
= 47pF
R
S
= 49.9Ω
R
L
= 1kΩ
10020-052
Figure 35. R
S
Test Circuit
Introducing a series resistor tends to isolate the capacitive load
from the feedback loop, thereby diminishing its influence. One
drawback to this approach is a slight loss of signal amplitude.
Figure 36 shows the effects of a series resistor on the capacitive
drive. For very large capacitive loads, the frequency response of
the amplifier is dominated by the roll-off of the series resistor
and capacitive load.
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 50 100 150 200 250
V
OUT
(V)
TIME (ns)
10020-135
+V
S
= 5V
R
L
= 1kΩ
C
L
= 47pF
NO R
S
R
S
= 49.9Ω
Figure 36. Pulse Response With and Without Series Resistor
Another method of reducing the resonant peaking caused by
driving large capacitive loads at the output of the ADA4830-1
and ADA4830-2 is with the use of a R-C shunt circuit or a snubber
circuit. This method acts to resistively load the amplifier output,
thus reducing frequency response peaking. One drawback to this
approach is a slight loss of signal bandwidth. Figure 37 shows a
simple circuit representation of the implementation of the R-C
snubber circuit with R
SNT
and C
SNT
. Figure 38 shows the effects of
a R-C snubber circuit driving 47 pF, where R
SNT
= 73.2 Ω and C
SNT
= 0.1 µF.
ADA4830-1
+
–
C
L
= 47pF
C
SNT
= 0.1uF
R
L
= 1kΩ
R
SNT
= 73.2Ω
10020-053
Figure 37. R-C Test Circuit
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 50 100 150 200 250
V
OUT
(V)
TIME (ns)
10020-137
+V
S
= 5V
R
L
= 1kΩ
C
L
= 47pF
NO SNUBBER
CIRCUIT
R
SNT
= 73.2Ω
C
SNT
= 0.1µF
Figure 38. Pulse Response With and Without R-C Snubber Circuit