LTC7891 datasheet(2/36 Pages) AD

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Data Sheet

LTC7891

TABLE OF CONTENTS

analog.com

Rev. 0 | 2 of 36

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

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

Typical Application Circuit .....................................1

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

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

Electrical Characteristics.................................... 3

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

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

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

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

Theory of Operation.............................................15

Functional Diagram.......................................... 15

Main Control Loop............................................15

Power and Bias Supplies (VIN, EXTVCC,

DRVCC, and INTVCC)......................................15

High-Side Bootstrap Capacitor.........................15

Dead Time Control (DTCA and DTCB Pins).... 16

Startup and Shutdown (RUN and

TRACK/SS Pins)............................................ 16

Light Load Operation: Burst Mode

Operation, Pulse Skipping Mode, or

Forced Continuous Mode (MODE Pin)...........16

Frequency Selection, Spread Spectrum,

and Phase-Locked Loop (FREQ and

PLLIN/SPREAD Pins).................................... 17

Output Overvoltage Protection......................... 17

Foldback Current..............................................17

Power Good..................................................... 17

Applications Information...................................... 18

Inductor Value Calculation................................18

Inductor Core Selection....................................18

Current Sense Selection.................................. 18

Low Value Resistor Current Sensing................19

Inductor DCR Current Sensing.........................19

Setting the Operating Frequency..................... 20

Selecting the Light Load Operating Mode........21

Dead Time Control (DTCA and DTCB Pins).... 21

CIN and COUT Selection....................................23

Setting the Output Voltage............................... 23

RUN Pin and Undervoltage Lockout................ 24

Soft Start and Tracking (TRACK/SS Pin)......... 24

INTVCC Regulators (OPTI-DRIVE)...................25

Topside FET Driver Supply (CB).......................26

Minimum On Time Considerations................... 26

Fault Conditions: Current Limit and Foldback.. 26

Fault Conditions: Overvoltage Protection.........27

Fault Conditions: Overtemperature

Protection....................................................... 27

Phase-Locked Loop and Frequency

Synchronization..............................................27

Efficiency Considerations................................. 27

Checking Transient Response......................... 28

Design Example............................................... 28

PCB Layout Checklist.......................................29

PCB Layout Debugging....................................30

Typical Applications..........................................32

Related Products..............................................35

Outline Dimensions............................................. 36

Ordering Guide.................................................36

Evaluation Boards............................................ 36

REVISION HISTORY

5/2022—Revision 0: Initial Version

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