Data Sheet

LT8645SA/LT8646SA

analog.com

Rev 0

2 of 39

TABLE OF CONTENTS

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

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

Simplified Application Diagram................................................................................................................................................................1

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

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

Absolute Maximum Ratings ......................................................................................................................................................................7

Thermal Resistance...............................................................................................................................................................................7

Pin Configurations and Function Descriptions........................................................................................................................................8

Typical Performance Characteristics .....................................................................................................................................................11

Block Diagram..........................................................................................................................................................................................20

Theory of Operation ................................................................................................................................................................................21

Applications Information ........................................................................................................................................................................22

Low EMI PCB Layout ...........................................................................................................................................................................22

Burst Mode Operation.........................................................................................................................................................................23

Forced Continuous Mode (FCM).........................................................................................................................................................24

Spread Spectrum Mode ......................................................................................................................................................................24

Synchronization ..................................................................................................................................................................................24

FB Resistor Network............................................................................................................................................................................25

Setting the Switching Frequency .......................................................................................................................................................25

Operating Frequency Selection and Trade-Offs ...............................................................................................................................26

Inductor Selection and Maximum Output Current ...........................................................................................................................26

Input Capacitors..................................................................................................................................................................................28

Output Capacitor and Output Ripple ................................................................................................................................................28

Ceramic Capacitors.............................................................................................................................................................................29

Enable Pin............................................................................................................................................................................................29

INTVCC Regulator..................................................................................................................................................................................29

Frequency Compensation (LT8646SA Only)......................................................................................................................................30

Output Voltage Tracking and Soft-Start............................................................................................................................................30

Output Power Good ............................................................................................................................................................................31

Paralleling (LT8646SA Only) ...............................................................................................................................................................31

Shorted and Reversed Input Protection............................................................................................................................................31

Thermal Considerations .....................................................................................................................................................................32

Typical Applications ................................................................................................................................................................................33

Related Parts............................................................................................................................................................................................36