ADT7490 datasheet(3/76 Pages) AD

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ADT7490

Rev. 0 | Page 3 of 76

TABLE OF CONTENTS

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

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

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

Functional Block Diagram ...............................................................2

Revision History ................................................................................3

Specifications .....................................................................................4

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

Thermal Characteristics...............................................................6

ESD Caution ..................................................................................6

Pin Configuration and Function Descriptions .............................7

Typical Performance Characteristics ..............................................9

Theory of Operation .......................................................................12

Feature Comparisons Between the ADT7490 and ADT7476A

.......................................................................................................12

Start-Up Operation .....................................................................13

Serial Bus Interface .....................................................................13

Write Operations.........................................................................14

Read Operations..........................................................................15

SMBus Timeout...........................................................................16

Voltage Measurement Input.......................................................16

Additional ADC Functions for Voltage Measurements.........17

Temperature Measurement........................................................19

Thermal Diode Temperature Measurement Method.............21

Series Resistance Cancellation ..................................................22

Factors Affecting Diode Accuracy............................................22

Additional ADC Functions for Temperature Measurement .23

Limits, Status Registers, and Interrupts .......................................25

Limit Values .................................................................................25

Interrupt Status Registers...........................................................26

THERM Timer ............................................................................28

Fan Drive Using PWM Control ................................................30

Laying Out 3-Wire Fans.............................................................32

Programming Trange .....................................................................35

Programming the Automatic Fan Speed Control loop ..............36

Manual Fan Control Overview .................................................36

THERM Operation in Manual Mode.......................................36

Automatic Fan Control Overview ............................................36

Step 1: Hardware Configuration ...............................................37

Step 2: Configuring the Muxtiplexer........................................37

Step 3: TMIN Settings for Thermal Calibration Channels .......38

Step 4: PWMMIN for Each PWM (Fan) Output .......................40

Step 5: PWMMAX for PWM (Fan) Outputs...............................40

Step 6: TRANGE for Temperature Channels ................................41

Step 7: T

THERM for Temperature Channels ................................43

Step 8: THYST for Temperature Channels...................................44

Programming the GPIOs ...........................................................46

XNOR Tree Test Mode ...............................................................46

Outline Dimensions........................................................................76

Ordering Guide ...........................................................................76

REVISION HISTORY

7/07—Revision 0: Initial Version

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