AD7745/AD7746

Rev. 0 | Page 2 of 28

TABLE OF CONTENTS

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

Timing Specifications....................................................................... 5

Absolute Maximum Ratings............................................................ 6

Pin Configurations and Function Descriptions ........................... 7

Typical Performance Characteristics ............................................. 8

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

Serial Interface ................................................................................ 12

Read Operation........................................................................... 12

Write Operation.......................................................................... 12

AD7745/AD7746 Reset ............................................................. 13

General Call................................................................................. 13

Register Descriptions ..................................................................... 14

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

Cap Data Register....................................................................... 15

VT Data Register ........................................................................ 15

Cap Set-Up Register ................................................................... 16

VT Set-Up Register .................................................................... 16

EXC Set-Up Register .................................................................. 17

Configuration Register .............................................................. 18

Cap DAC A Register................................................................... 19

Cap DAC B Register................................................................... 19

Cap Offset Calibration Register................................................ 19

Cap Gain Calibration Register.................................................. 19

Volt Gain Calibration Register ................................................. 19

Circuit Description......................................................................... 20

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

Capacitance-to-Digital Converter ........................................... 20

Excitation Source........................................................................ 20

CAPDAC ..................................................................................... 21

Single-Ended Capacitive Input................................................. 21

Differential Capacitive Input .................................................... 21

Parasitic Capacitance to Ground.............................................. 22

Parasitic Resistance to Ground................................................. 22

Parasitic Parallel Resistance ...................................................... 22

Parasitic Serial Resistance ......................................................... 23

Capacitive Gain Calibration ..................................................... 23

Capacitive System Offset Calibration ...................................... 23

Internal Temperature Sensor .................................................... 23

External Temperature Sensor ................................................... 24

Voltage Input............................................................................... 24

VDD Monitor ................................................................................ 24

Typical Application Diagram.................................................... 24

Outline Dimensions ....................................................................... 25

Ordering Guide .......................................................................... 25

REVISION HISTORY

4/05—Revision 0: Initial Version