AD8420ARMZ-R7 datasheet(24/27 Pages) AD

24 / 27 page

Data Sheet

AD8420

Rev. A | Page 23 of 26

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 with 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 intro-

duced 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/digitalpotentiometers.

+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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