Data Sheet

LTC7897

analog.com

Rev. A

2 of 53

TABLE OF CONTENTS

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

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

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

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

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

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

Absolute Maximum Ratings ......................................................................................................................................................................9

Pin Configurations and Function Descriptions......................................................................................................................................11

Block Diagram..........................................................................................................................................................................................14

Typical Performance Characteristics .....................................................................................................................................................15

Theory of Operation ................................................................................................................................................................................20

Main Control Loop...............................................................................................................................................................................20

Power and Bias Supplies (VIN, EXTVCC, DRVCC, and INTVCC) ................................................................................................................20

High-Side Bootstrap Capacitor ..........................................................................................................................................................20

Dead Time Control (DTCA and DTCB Pins) ........................................................................................................................................20

Start-Up and Shutdown (RUN, OVLO, and TRACK/SS Pins) .............................................................................................................21

Light Load Operation: Burst Mode Operation, Pulse-Skipping Mode, or Forced Continuous Mode (MODE Pin).........................21

Frequency Selection, Spread Spectrum, and PhaseLocked Loop (FREQ and PLLIN/SPREAD Pins).............................................22

Input Supply Overvoltage Lockout (OVLO Pin).................................................................................................................................23

Output Overvoltage Protection..........................................................................................................................................................23

Foldback Current ................................................................................................................................................................................23

Power Good .........................................................................................................................................................................................23

Applications Information ........................................................................................................................................................................24

Inductor Value Calculation.................................................................................................................................................................24

Inductor Core Selection......................................................................................................................................................................24

Current Sense Selection .....................................................................................................................................................................24

Low Value Resistor Current Sensing ..................................................................................................................................................25

Inductor DCR Current Sensing ...........................................................................................................................................................26

Setting the Operating Frequency ..................................................................................................................................................27

Selecting the Light-Load Operating Mode ....................................................................................................................................28

Dead Time Control (DTCA and DTCB Pins)....................................................................................................................................29

DTCX Pins Tied to INTVCC or Ground (Adaptive Dead Time Control) ............................................................................................29

DTCX Pin Connected with a Resistor to GND .................................................................................................................................30

Power MOSFET Selection...............................................................................................................................................................31