ADA4700-1ARDZ-R7 datasheet(23/28 Pages) AD

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Data Sheet

ADA4700-1

DRIVING CAPACITIVE LOADS

Although the ADA4700-1 behaves well when driving capacitive

loads, CL, as seen in Figure 27 to Figure 30, extra compensation

can improve the response when large capacitances need to be

accommodated. The simplest way of accomplishing this is with

a snubber network, as shown in Figure 61.

Figure 61. Snubber Network

For unity-gain applications and capacitive loads up to 1 nF,

RSNUB = 150 Ω and CSNUB = 10 nF works well. Results for this

circuit are shown in Figure 64. With higher closed-loop gains,

lighter snubbing can be used. For capacitive loads up to 10 nF, the

snubber must be larger. Figure 65 shows the results of using an

RSNUB = 22 Ω, CSNUB = 100 nF, and CL = 10 nF with the ADA4700-1

in a gain of 10. Because the snubber network places an ac load on

the amplifier, snubbing does not work well when larger capacitive

loads are used, or when large transients are present. A better

approach is to use a bypass network in the feedback path, as

shown in Figure 62.

Figure 62. Unity-Gain Configuration with Bypass Network

The bypass network in Figure 62 performs well with loads up to

100 nF. The resulting waveforms are shown in Figure 66 for various

output amplitudes. For heavier loads, capacitive feedback, CFB, must

be increased. The configuration in Figure 62 can be modified to

work with gains greater than 1. Figure 63 shows a bypass network

with a gain of 10 system, and results for various output amplitudes

are shown in Figure 67.

Figure 63. Bypass Network with Gain of 10 System

Figure 64. Results from Snubber Network with AV = +1 and CL = 10 pF to 1 nF

Figure 65. Results from Snubber Network with Higher Gains, CL = 10 nF

Figure 66. Results of Bypass Network for Various Output Amplitudes,

Unity Gain with CL = 100 nF

RSNUB

VOUT

VIN

CSNUB

VOUT

VIN

3.3kΩ

22Ω

10nF

CFB

VOUT

VIN

3.3kΩ

CFB

5.1kΩ

43kΩ

22Ω

–10

–8

–6

–4

–2

TIME (µs)

OUTPUT

INPUT

VSY = ±50V

AV = +1

CL = 10pF TO 1nF

–15

–10

–5

0.2

0.4

0.6

0.8

TIME (ms)

1.0

1.2

1.4

VSY = ±50V

AV = +10

CL = 10nF

–10

–8

–6

–4

–2

0.2

0.4

0.6

TIME (ms)

0.8

1.0

1.2

VSY = ±50V

AV = +1

CL = 100nF

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