AD7731(1997) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD7731
(Rev.:1997)

Low Noise, High Throughput 24-Bit Sigma-Delta ADC

Analog Devices 

AD7731

BURNOUT CURRENTS

TWO 100nA BURNOUT

CURRENTS ALLOW THE

USER TO EASILY DETECT

IF A TRANSDUCER HAS

BURNT OUT OR GONE

OPEN-CIRCUIT

SEE PAGE 23

BUFFER AMPLIFIER

THE BUFFER AMPLIFIER

PRESENTS A HIGH

IMPEDANCE INPUT STAGE

FOR THE ANALOG INPUTS

ALLOWING SIGNIFICANT

EXTERNAL SOURCE

IMPEDANCES

SEE PAGE 23

AVDD

AIN1

AVDD

PROGRAMMABLE GAIN

AMPLIFIER

DIFFERENTIAL

REFERENCE

THE PROGRAMMABLE

GAIN AMPLIFIER ALLOWS

SEVEN UNIPOLAR AND

SEVEN BIPOLAR INPUT

RANGES FROM +20mV TO

+1.28V

SEE PAGE 23

THE REFERENCE INPUT TO THE

PART IS DIFFERENTIAL AND

FACILITATES RATIOMETRIC

OPERATION. THE REFERENCE

VOLTAGE CAN BE SELECTED TO

BE NOMINALLY +2.5V OR +5V.

REFERENCE DETECT CIRCUITRY

TESTS FOR OPEN OR SHORTED

REFERENCES

SEE PAGE 24

DVDD

REF IN(–) REF IN(+)

SIGMA-DELTA ADC

THE SIGMA-DELTA

ARCHITECTURE ENSURES

24 BITS NO MISSING

CODES. THE ENTIRE

SIGMA-DELTA ADC CAN BE

CHOPPED TO REMOVE

DRIFT ERRORS

SEE PAGE 24

PROGRAMMABLE

DIGITAL FILTER

TWO STAGE FILTER THAT

ALLOWS PROGRAMMING OF

OUTPUT UPDATE RATE AND

SETTLING TIME AND THAT

HAS A FASTSTEPTM MODE

(SEE FIGURE 3)

SEE PAGE 24

STANDBY MODE

THE STANDBY MODE

REDUCES POWER

CONSUMPTION TO 50␮W

SIGMA-DELTA A/D CONVERTER

STANDBY

SEE PAGE 32

AIN2

AIN3/D1

MUX

PGA

SIGMA-

DELTA

MODULATOR

PROGRAMMABLE

DIGITAL

FILTER

SYNC

CLOCK OSCILLATOR

CIRCUIT

AIN4/D0

AIN5

AIN6

AGND

BUFFER

SERIAL INTERFACE

AND CONTROL LOGIC

CLOCK

GENERATION

REGISTER BANK

MCLK IN

MCLK OUT

SCLK

THE CLOCK SOURCE FOR THE

PART CAN BE PROVIDED BY

AN EXTERNALLY-APPLIED

CLOCK OR BY CONNECTING A

CRYSTAL OR CERAMIC

RESONATOR ACROSS THE

CLOCK PINS

SEE PAGE 31

ANALOG MULTIPLEXER

A DIFFERENTIAL MULTIPLEXER

ALLOWS SELECTION OF THREE

FULLY DIFFERENTIAL PAIRS OR

FIVE PSEUDO-DIFFERENTIAL INPUT

PAIRS TO BE SWITCHED TO THE

BUFFER AMPLIFIER. THE

MULTIPLEXER IS CONTROLLED

VIA THE SERIAL INTERFACE

SEE PAGE 23

AD7731

CALIBRATION

MICROCONTROLLER

AGND

DGND

POL

RDY

OUTPUT DRIVERS

THE AIN3 AND AIN4 INPUT

CHANNELS CAN BE

RECONFIGURED TO BECOME

TWO OUTPUT DIGITAL PORT

LINES THAT CAN BE

PROGRAMMED OVER THE

SERIAL INTERFACE

SEE PAGE 32

CALIBRATION

MICROCONTROLLER

THE AD7731 OFFERS A

NUMBER OF DIFFERENT

CALIBRATION OPTIONS

INCLUDING SELF AND

SYSTEM CALIBRATION

SEE PAGE 28

CS

DIN

DOUT

RESET

REGISTER BANK

TWELVE REGISTERS CONTROL

ALL FUNCTIONS ON THE PART

AND PROVIDE STATUS

INFORMATION AND

CONVERSION RESULTS

SEE PAGE 20

SERIAL INTERFACE

SPI*-COMPATIBLE OR DSP-

COMPATIBLE SERIAL

INTERFACE THAT CAN BE

OPERATED FROM JUST THREE

WIRES. ALL FUNCTIONS ON THE

PART (APART FROM MASTER

RESET) CAN BE ACCESSED VIA

THE SERIAL INTERFACE

SEE PAGE 33

*SPI IS A TRADEMARK OF MOTOROLA, INC.

Figure 2. Detailed Functional Block Diagram

–6–

REV. 0

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