EVAL-AD421EB View Datasheet(PDF) - Analog Devices

Part Name

Description

MFG CO.

EVAL-AD421EB

Loop-Powered 4 mA to 20 mA DAC

Analog Devices 

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AD421

0.1␮F

SENSORS

RTD

mV ⍀ TC

AMBIENT

TEMP

SENSOR

DVDD AVDD

REF IN

ANALOG

TO

DIGITAL

CONVERTER

AD7714/

AD7715

MCLK IN

MCLK OUT

CS

DATA OUT

SCLK

DATA IN

DGND AGND

3.3V

2.2␮F

DN25D

0.01␮F

100k⍀

4.7␮F

VCC

MICROCONTROLLER

GND

1.25V

4.7␮F

BOOST VCC

REF OUT1

REF OUT2

REF IN

LV

0.01␮F

COMP

CLOCK

LATCH

DATA

AD421

DRIVE

1k⍀

1000pF

COM

C1 C2 C3

LOOP

RTN

CC*

LOOP

POWER

HART

MODEM

BELL 202

WAVEFORM

SHAPER

BANDPASS

FILTER

HT20C12/20C15

*FOR SELECTION OF CC, REFER TO AN-534

Figure 17. AD421 in HART Transmitter Application

Current Source

Figure 18 shows an application circuit for the AD421 being

used as a current source. The current programmed to the

AD421 (4 mA to 20 mA) will develop a voltage across R1.

This same voltage due to negative feedback will be generated

across R2. The ratio of R1 to R2 determines the current that

flows in the load resistor RL. IL = [1 + R1/R2] × IPROG, where IL

is the current that flows in the load resistor RL and IPROG is the

current programmed to the AD421. R1 and R2 are external to

the AD421 and will need to be matched resistors to obtain a

highly accurate current source.

DATA

CLOCK

LATCH

5 VOLT

+5V

REGULATOR

OUT

IN

VS

10k⍀

10k⍀

4.7␮F

COM

2.2␮F

COM

10k⍀

REF IN REF OUT2 REF OUT1

LV

VCC

COM

DATA

DRIVE

COMP

CLOCK

AD421

BOOST

LOOP

RTN

LATCH

COM C1

C2

C3

R1

R2

0.01␮F

0.01␮F

0.0033␮F

RL

Figure 18. AD421 in Programmable Current Source/Sink

VS RETURN

–12–

REV. C

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