AD7785BRUZ Datasheet AD7785BRUZ | P1-P3

3-Channel, Low Noise, Low Power, 20-Bit ∑-Δ

ADC with On-Chip In-Amp and Reference

AD7785

Rev. 0

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FEATURES

Up to 20 bits effective resolution

RMS noise

40 nV @ 4.17 Hz

85 nV @ 16.7 Hz

Current: 400 μA typical

Power-down: 1 μA maximum

Low noise programmable gain instrumentation amp

Band gap reference with 4 ppm/°C drift typical

Update rate: 4.17 Hz to 470 Hz

3 differential inputs

Internal clock oscillator

Simultaneous 50 Hz/60 Hz rejection

Programmable current sources

On-chip bias voltage generator

Burnout currents

Power supply: 2.7 V to 5.25 V

–40°C to +105°C temperature range

Independent interface power supply

16-lead TSSOP package

Interface

3-wire serial

SPI®, QSPI™, MICROWIRE™, and DSP compatible

Schmitt trigger on SCLK

APPLICATIONS

Thermocouple measurements

RTD measurements

Thermistor measurements

Gas analysis

Industrial process control

Instrumentation

Portable instrumentation

Blood analysis

Smart transmitters

Liquid/gas chromatography

6-digit DVM

GENERAL DESCRIPTION

The AD7785 is a low power, low noise, complete analog front

end for high precision measurement applications. The AD7785

contains a low noise 20-bit ∑-Δ ADC with three differential

analog inputs. The on-chip, low noise instrumentation amplifier

means that signals of small amplitude can be interfaced directly

to the ADC. With a gain setting of 64, the rms noise is 40 nV

when the update rate equals 4.17 Hz.

The device contains a precision low noise, low drift internal

band gap reference and can accept an external differential

reference. Other on-chip features include programmable

excitation current sources, burnout currents, and a bias voltage

generator. The bias voltage generator sets the common-mode

voltage of a channel to AV

/2.

The AD7785 can be operated with either the internal clock

or an external clock. The output data rate from the device is

software-programmable and can be varied from 4.17 Hz to 470

Hz. The device operates with a power supply from 2.7 V to

5.25 V. It consumes a current of 400 μA typical and is housed in

a 16-lead TSSOP package.

FUNCTIONAL BLOCK DIAGRAM

06721-001

DOUT/RD

DIN

SCLK

SERIAL

INTERFACE

AND

CONTROL

LOGIC

Σ-Δ

ADC

AD7785

AIN1(+)

AIN1(–)

AIN2(+)

AIN2(–)

GND

MUX

BIAS

BAND GAP

REFERENCE

INTERNAL

CLOCK

CLK

GND

REFIN(–)/AIN3(–)

IOUT1

IOUT2

IN-AMPBUF

REFIN(+)/AIN3(+)

Figure 1.

AD7785* PRODUCT PAGE QUICK LINKS

Last Content Update: 02/23/2017

COMPARABLE PARTS

View a parametric search of comparable parts.

EVALUATION KITS

• AD7785 Evaluation Board

DOCUMENTATION

Application Notes

• AN-101: Cross Plot Generator Allows Quick A/D Converter

Evaluation

• AN-202: An IC Amplifier User’s Guide to Decoupling,

Grounding, and Making Things Go Right for a Change

• AN-283: Sigma-Delta ADCs and DACs

• AN-311: How to Reliably Protect CMOS Circuits Against

Power Supply Overvoltaging

• AN-347: Shielding and Guarding

• AN-388: Using Sigma-Delta Converters-Part 1

• AN-389: Using Sigma-Delta Converters-Part 2

• AN-397: Electrically Induced Damage to Standard Linear

Integrated Circuits:

• AN-607: Selecting a Low Bandwidth (<15 kSPS) Sigma-

Delta ADC

• AN-615: Peak-to-Peak Resolution Versus Effective

Resolution

• AN-880: ADC Requirements for Temperature

Measurement Systems

• AN-968: Current Sources: Options and Circuits

Data Sheet

• AD7785: 3-Channel, Low Noise, Low Power, 20-Bit Σ-Δ

ADC with On-Chip In-Amp and Reference Data Sheet

TOOLS AND SIMULATIONS

• AD7785/AD7790/AD7791/AD7792/AD7793/AD7794/

AD7795/AD7796/AD7797/AD7798/AD7799 Digital Filter

Model

• Sigma-Delta ADC Tutorial

REFERENCE MATERIALS

Technical Articles

• High-resolution ADCs — an overview

• MS-2210: Designing Power Supplies for High Speed ADC

DESIGN RESOURCES

• AD7785 Material Declaration

• PCN-PDN Information

• Quality And Reliability

• Symbols and Footprints

DISCUSSIONS

View all AD7785 EngineerZone Discussions.

SAMPLE AND BUY

Visit the product page to see pricing options.

TECHNICAL SUPPORT

Submit a technical question or find your regional support

number.

DOCUMENT FEEDBACK

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AD7785

Rev. 0 | Page 2 of 32

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications....................................................................................... 1

General Description......................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 2

Specifications..................................................................................... 3

Timing Characteristics..................................................................... 6

Timing Diagrams.......................................................................... 7

Absolute Maximum Ratings............................................................ 8

ESD Caution.................................................................................. 8

Pin Configuration and Function Descriptions............................. 9

Output Noise and Resolution Specifications .............................. 11

External Reference...................................................................... 11

Internal Reference ...................................................................... 12

Typical Performance Characteristics ........................................... 13

On-Chip Registers.......................................................................... 14

Communications Register......................................................... 14

Status Register............................................................................. 15

Mode Register ............................................................................. 15

Configuration Register .............................................................. 17

Data Register............................................................................... 18

ID Register................................................................................... 18

IO Register................................................................................... 18

Offset Register ............................................................................ 19

Full-Scale Register...................................................................... 19

ADC Circuit Information.............................................................. 20

Overview ..................................................................................... 20

Digital Interface.......................................................................... 21

Circuit Description......................................................................... 25

Analog Input Channel ............................................................... 25

Instrumentation Amplifier........................................................ 25

Bipolar/Unipolar Configuration .............................................. 25

Data Output Coding .................................................................. 25

Burnout Currents ....................................................................... 26

Excitation Currents.................................................................... 26

Bias Voltage Generator .............................................................. 26

Reference ..................................................................................... 26

Reset ............................................................................................. 26

Monitor ............................................................................. 27

Calibration................................................................................... 27

Grounding and Layout .............................................................. 27

Applications Information.............................................................. 29

Temperature Measurement using a Thermocouple............... 29

Temperature Measurement using an RTD.............................. 30

Outline Dimensions ....................................................................... 31

Ordering Guide .......................................................................... 31

REVISION HISTORY

4/07—Revision 0: Initial Version

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P33

AD7785BRUZ

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Manufacturer:

Analog Devices Inc.

Description:

Analog to Digital Converters - ADC 3Ch Lo Noise Lo Pwr 20B w/ On-Chip Ref

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AD7785BRUZ