ADA4830-2BCPZ-R2 datasheet(17/22 Pages) AD

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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, RS, in series with the

capacitive load. Figure 35 shows the test circuit.

ADA4830-1

–

CL = 47pF

RS = 49.9Ω

RL = 1kΩ

Figure 35. RS 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

100

150

200

250

TIME (ns)

+VS = 5V

RL = 1kΩ

CL = 47pF

NO RS

RS = 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 RSNT and CSNT. Figure 38 shows the effects of

a R-C snubber circuit driving 47 pF, where RSNT = 73.2 Ω and CSNT

= 0.1 µF.

ADA4830-1

–

CL = 47pF

CSNT = 0.1uF

RL = 1kΩ

RSNT = 73.2Ω

Figure 37. R-C Test Circuit

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100

150

200

250

TIME (ns)

+VS = 5V

RL = 1kΩ

CL = 47pF

NO SNUBBER

CIRCUIT

RSNT = 73.2Ω

CSNT = 0.1µF

Figure 38. Pulse Response With and Without R-C Snubber Circuit

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