ADA4700-1ARDZ-R7 datasheet(24/28 Pages) AD

24 / 28 page

ADA4700-1

Data Sheet

Figure 67. Result of Bypass Network with AV = +10 and CL = 100 nF

INCREASING CURRENT DRIVE

Extra output current can be obtained by adding external driver

transistors. Crossover distortion is minimized by allowing the

amplifier to drive the lower currents directly via the bypass

resistor, as is shown in Figure 68. This circuit can provide a few

hundred miliamps; however, keep the driver transistors within

their safe operating area. For heavier loads (up to 5 A), power

Darlingtons can be used, as is shown in Figure 69.

Figure 68. Increasing Current Drive Using Discrete Transistors

Figure 69. Bilateral Current Source with Transfer Function 1 mA/V

CONSTANT CURRENT APPLICATIONS

When a constant current with high compliance is needed, the

ADA4700-1 can be used as a modified Howland current pump.

The values shown in Figure 70 yield a transfer function of 1 mA/V.

Applying this analysis to the modified Howland current pump

in Figure 71 results in an output capability of 1 A/V.

Figure 70. Transfer Function of 1 mA/V

Figure 71. Modified Howland Current Pump

–50

–40

–30

–20

–10

0.5

1.0

TIME (ms)

1.5

2.0

VSY = ±50V

AV = +10

CL = 100nF

IOUT

VIN

180Ω

2N5550

2N5401

IOUT

VIN

270Ω

–V

BDW93C

BDW94C

100kΩ

49.5kΩ

RSET

500Ω

IOUT =

50kΩ

100kΩ

+VIN

IOUT

RSET

–VIN

IF R2 = R4 + RSET

AND R1 = R3

BDW93C

BDW94C

10kΩ

20kΩ

IOUT

VIN

270Ω

0.5Ω

–V

20kΩ

10kΩ

Rev. 0 | Page 24 of 28

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