AD8420ARMZ-R7 datasheet(23/28 Pages) AD

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Data Sheet

AD8420

Rev. 0 | Page 23 of 28

OUTPUT BUFFERING

The AD8420 is designed to drive loads of 20 kΩ or greater but

can deliver up to 10 mA to heavier loads at lower output voltage

swings (see Figure 42). If more output current is required, buffer

the AD8420 output with a precision op amp. Figure 67 shows

the recommended configuration using the ADA4692-2 as a single

supply. This low power op amp can swing its output from 1 V to

4 V on a single 5 V supply while sourcing or sinking more than

30 mA of current. When using this configuration, the load seen

by the AD8420 is approximately R1 + R2.

+5V

–VS

+VS

–VS

+VS

0.1µF

VOUT

0.1µF

ADA4692-2

VIN

AD8420

VREF

Figure 67. Output Buffering

Because the ADA4692-2 is a dual op amp, another op amp is

now free for use as an active filter stage or to buffer another

AD8420 output on the same PCB. Figure 68 shows another

suggestion for how to use this second op amp. In this circuit,

the voltage from the wiper of a potentiometer is buffered by the

ADA4692-2, allowing a variable level shift of the output. Resistors

above and below the potentiometer reduce the total range of the

level shift but increase the precision. If the potentiometer were

connected directly to the REF pin of the AD8420, gain error would

be introduced from the variable resistance. The potentiometer can

be tuned in hardware or software, depending on the type of

potentiometer chosen. For a list of digital potentiometers made

by Analog Devices, Inc., visit www.analog.com/digipots/.

+5V

0.1µF

VOUT

0.1µF

ADA4692-2

VIN

AD8420

REF

CCW

SUGGESTION FOR SECOND

AMPLIFIER: VARIABLE

LEVEL SHIFT WITHOUT

AFFECTING GAIN

Figure 68. Variable Level Shift

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