AD7730LBR datasheet(6/52 Pages) AD

6 / 52 page

AD7730/AD7730L

–6–

REV. A

Figure 2. Detailed Functional Block Diagram

SIGMA-

DELTA

MODULATOR

AD7730

6-BIT

DAC

SERIAL INTERFACE

AND CONTROL LOGIC

CLOCK

GENERATION

PROGRAMMABLE

DIGITAL

FILTER

SIGMA-DELTA A/D CONVERTER

BUFFER

PGA

AGND

AVDD

VBIAS

AIN1(+)

AIN1(–)

AIN2(+)/D1

AIN2(–)/D0

ACX

STANDBY

SYNC

MCLK IN

MCLK OUT

SCLK

DIN

DOUT

RESET

RDY

POL

DGND

AGND

AVDD

DVDD

REF IN(–) REF IN(+)

MUX

REFERENCE DETECT

EXCITATION

CLOCK

CALIBRATION

MICROCONTROLLER

THIRTEEN REGISTERS CONTROL

ALL FUNCTIONS ON THE PART AND

PROVIDE STATUS INFORMATION

AND CONVERSION RESULTS

SEE PAGE 11

STANDBY MODE

THE STANDBY MODE REDUCES

POWER CONSUMPTION TO 5 A

SEE PAGE 33

CLOCK OSCILLATOR

CIRCUIT

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 32

SERIAL INTERFACE

SPI*-COMPATIBLE OR DSP-

COMPATIBLE SERIAL INTERFACE

WHICH CAN BE OPERATED FROM

JUST THREE WIRES. ALL

FUNCTIONS ON THE PART

CAN BE ACCESSED VIA

THE SERIAL INTERFACE

SEE PAGE 35

OFFSET/TARE DAC

ALLOWS A PROGRAMMED

VOLTAGE TO BE EITHER ADDED

OR SUBTRACTED FROM THE

ANALOG INPUT SIGNAL BEFORE

IT IS APPLIED TO THE PGA

SEE PAGE 24

OUTPUT DRIVERS

THE SECOND ANALOG INPUT

CHANNEL CAN BE

RECONFIGURED TO BECOME TWO

OUTPUT DIGITAL PORT LINES

WHICH CAN BE PROGRAMMED

OVER THE SERIAL INTERFACE

SEE PAGE 33

AC EXCITATION

FOR AC-EXCITED BRIDGE

APPLICATIONS, THE ACX

OUTPUTS PROVIDE SIGNALS

THAT CAN BE USED TO SWITCH

THE POLARITY OF THE BRIDGE

EXCITATION VOLTAGE

SEE PAGE 41

ANALOG MULTIPLEXER

A TWO-CHANNEL DIFFERENTIAL

MULTIPLEXER SWITCHES ONE OF

THE TWO DIFFERENTIAL INPUT

CHANNELS TO THE BUFFER

AMPLIFIER. THE MULTIPLEXER IS

CONTROLLED VIA THE SERIAL

INTERFACE

SEE PAGE 24

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

DIFFERENTIAL

REFERENCE

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

SEE PAGE 25

PROGRAMMABLE

DIGITAL FILTER

TWO STAGE FILTER THAT

ALLOWS PROGRAMMING OF

OUTPUT UPDATE RATE AND

SETTLING TIME AND WHICH HAS

A FAST STEP MODE

(SEE FIGURE 3)

SEE PAGE 26

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 26

PROGRAMMABLE GAIN

AMPLIFIER

THE PROGRAMMABLE GAIN

AMPLIFIER ALLOWS FOUR

UNIPOLAR AND FOUR BIPOLAR

INPUT RANGES FROM

+10mV TO +80mV

SEE PAGE 24

BUFFER AMPLIFIER

THE BUFFER AMPLIFIER

PRESENTS A HIGH IMPEDANCE

INPUT STAGE FOR THE ANALOG

INPUTS ALLOWING SIGNIFICANT

EXTERNAL SOURCE

IMPEDANCES

SEE PAGE 24

BURNOUT CURRENTS

TWO 100nA BURNOUT

CURRENTS ALLOW THE USER

TO EASILY DETECT IF A

TRANSDUCER HAS BURNT

OUT OR GONE OPEN-CIRCUIT

SEE PAGE 25

+/–

*SPI IS A TRADEMARK OF MOTOROLA, INC.

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