AD7798BRUZ Datasheet AD7799BRUZ-REEL, AD7798BRUZ, AD7799BRUZ | P1-P3

Channel, Low Noise, Low Power,

16-/24-Bit,

ADC with On-Chip In-Amp

Data Sheet

AD7798/AD7799

Rev. B Document Feedback

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FEATURES

RMS noise:

27 nV at 4.17 Hz (AD7799)

65 nV at 16.7 Hz (AD7799)

40 nV at 4.17 Hz (AD7798)

85 nV at 16.7 Hz (AD7798)

Current: 380 µA typical

Power-down: 1 µA maximum

Low noise, programmable gain, instrumentation amp

Update rate: 4.17 Hz to 470 Hz

3 differential inputs

Internal clock oscillator

Simultaneous 50 Hz/60 Hz rejection

Reference detect

Low-side power switch

Programmable digital outputs

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

Weigh scales

Pressure measurement

Strain gauge transducers

Gas analysis

Industrial process control

Instrumentation

Portable instrumentation

Blood analysis

Smart transmitters

Liquid/gas chromotography

6-digit DVM

FUNCTIONAL BLOCK DIAGRAM

DOUT/RDY

DIN

SCLK

SERIAL

INTERFACE

AND

CONTROL

LOGIC

Σ-Δ

ADC

AD7798/AD7799

AD7798: 16-BIT

AD7799: 24-BIT

AIN2(+)

AIN2(–)

AIN3(+)/P1

AIN1(+)

AIN1(–)

AIN3(–)/P2

GND

MUX

INTERNAL

CLOCK

GND

REFIN(–)

PSW

IN-AMP

REFERENCE

DETECT

REFIN(+)

04856-001

Figure 1.

GENERAL DESCRIPTION

The AD7798/AD7799 are low power, low noise, complete

analog front ends for high precision measurement applications.

The AD7798/AD7799 contains a low noise, 16-/24-bit ∑-∆

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 27 nV for the AD7799 and 40 nV

for the AD7798 when the update rate equals 4.17 Hz.

On-chip features include a low-side power switch, reference

detect, programmable digital output pins, burnout currents,

and an internal clock oscillator. The output data rate from the

part is software-programmable and can be varied from 4.17 Hz

to 470 Hz.

The part operates with a power supply from 2.7 V to 5.25 V.

The AD7798 consumes a current of 300 µA typical, whereas the

AD7799 consumes 380 µA typical. Both devices are housed in a

16-lead TSSOP package.

AD7798/AD7799 Data Sheet

Rev. B | Page 2 of 28

TABLE OF CONTENTS

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

Interface ............................................................................................. 1

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

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

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

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

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

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

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

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

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

Output Noise and Resolution Specifications .............................. 10

AD7798 ........................................................................................ 10

AD7799 ........................................................................................ 11

Typical Performance Characteristics ........................................... 12

On-Chip Registers .......................................................................... 13

Communication Register .......................................................... 13

Status Register ............................................................................. 14

Mode Register ............................................................................. 14

Configuration Register .............................................................. 16

Data Register ............................................................................... 17

ID Register ................................................................................... 17

IO Register................................................................................... 17

Offset Register ............................................................................ 17

Full-Scale Register ...................................................................... 17

ADC Circuit Information.............................................................. 18

Overview ..................................................................................... 18

Digital Interface .......................................................................... 19

Circuit Description......................................................................... 22

Analog Input Channel ............................................................... 22

Instrumentation Amplifier........................................................ 22

Bipolar/Unipolar Configuration .............................................. 22

Data Output Coding .................................................................. 23

Burnout Currents ....................................................................... 23

Reference ..................................................................................... 23

Reference Detect ......................................................................... 23

Reset ............................................................................................. 23

Monitor ............................................................................. 24

Calibration................................................................................... 24

Grounding and Layout .............................................................. 25

Applications Information .............................................................. 26

Weigh Scales ................................................................................ 26

Outline Dimensions ....................................................................... 27

Ordering Guide .......................................................................... 27

REVISION HISTORY

7/13—Rev. A to Rev. B

Changes to Table 3 ............................................................................ 8

Changes to Digital Interface Section ............................................ 19

Changes to Ordering Guide .......................................................... 27

3/07—Rev. 0 to Rev. A

Updated Format .................................................................. Universal

Changes to Specifications ................................................................ 3

Changes to Table 5 and Table 6 ..................................................... 10

Changes to Table 7 and Table 8 ..................................................... 11

Changes to Table 14 ........................................................................ 15

Changes to Ordering Guide .......................................................... 27

1/05—Revision 0: Initial Version

Data Sheet AD7798/AD7799

Rev. B | Page 3 of 28

SPECIFICATIONS

= 2.7 V to 5.25 V; DV

= 2.7 V to 5.25 V; GND = 0 V; REFIN(+) = AV

; REFIN(−) = 0 V. All specifications T

MIN

to T

MAX

, unless

otherwise noted.

Table 1.

Parameter AD7798B/AD7799B

Unit Test Conditions/Comments

ADC CHANNEL

Output Update Rate 4.17 − 470 Hz nom

No Missing Codes

24 Bits min AD7799: f

ADC

< 242 Hz

16 Bits min AD7798

Resolution See Table 5 to Table 8

Output Noise and Update Rates

See Table 5 to Table 8

Integral Nonlinearity ±15 ppm of FSR max

Offset Error

±1 µV typ

Offset Error Drift vs. Temperature

±10 nV/°C typ

Full-Scale Error

3, 5

±10 µV typ

Gain Drift vs. Temperature

±1 ppm/°C typ

Power Supply Rejection 100 dB min AIN = 1 V/gain, gain ≥ 4

ANALOG INPUTS

Differential Input Voltage Ranges ±V

REF

/gain V nom V

REF

= REFIN(+) – REFIN(–), gain = 1 to 128

Absolute AIN Voltage Limits

Unbuffered Mode GND − 30 mV V min Gain = 1 or 2

+ 30 mV V max

Buffered Mode GND + 100 mV V min Gain = 1 or 2

– 100 mV

V max

In-Amp Active GND + 300 mV V min Gain = 4 to 128

− 1.1 V max

Common-Mode Voltage, V

0.5 V min V

= (AIN(+) + AIN(−))/2, gain = 4 to 128

Analog Input Current

Buffered Mode or In-Amp Active

Average Input Current

±1 nA max Gain = 1 or 2, update rate < 100 Hz

±250 pA max Gain = 4 to 128, update rate < 100 Hz

±1 nA max AIN3(+)/AIN3(−), update rate < 100 Hz

Average Input Current Drift ±2 pA/°C typ

Unbuffered Mode Gain = 1 or 2

Average Input Current ±400 nA/V typ Input current varies with input voltage

Average Input Current Drift ±50 pA/V/°C typ

Normal Mode Rejection

@ 50 Hz, 60 Hz 65 dB min 80 dB typ, 50 ± 1 Hz, 60 ± 1 Hz (FS[3:0] = 1010)

@ 50 Hz 80 dB min 90 dB typ, 50 ± 1 Hz (FS[3:0] = 1001)

@ 60 Hz 90 dB min 100 dB typ, 60 ± 1 Hz (FS[3:0] = 1000)

Common-Mode Rejection

@ DC 100 dB min AIN = 1 V/gain, gain ≥ 4

@ 50 Hz, 60 Hz

100 dB min 50 ± 1 Hz, 60 ± 1 Hz (FS[3:0] = 1010)

@ 50 Hz, 60 Hz

100 dB min 50 ± 1 Hz (FS[3:0] = 1001

), 60 ± 1 Hz

(FS[3:0] = 1000

)

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

AD7798BRUZ

Mfr. #:

Buy AD7798BRUZ

Manufacturer:

Analog Devices Inc.

Description:

Analog to Digital Converters - ADC 3-Ch 16-Bit Low Noise Low Power

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AD7798BRUZ

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