LTC3889 datasheet(2/118 Pages) AD

2 / 118 page

LTC3888/LTC3888-1/

LTC3888-2

Rev. B

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TABLE OF CONTENTS

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

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

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

Description.................................................. 1

Absolute Maximum Ratings.............................. 5

Pin Configuration .......................................... 5

Pin Configuration .......................................... 6

Order Information.......................................... 7

Electrical Characteristics................................. 7

Typical Performance Characteristics ..................12

Pin Functions ..............................................15

Block Diagram.............................................17

Test Circuit.................................................18

PMBus Timing Diagram..................................19

SPI Timing Diagram......................................19

Operation...................................................20

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

About This Document.........................................20

Major Product Features ..........................................20

Main Control Loop..................................................21

Power-Up and Initialization .....................................21

Testing Integrity of Output Voltage Sense .......... 24

Analog Output Voltage Control (LTC3888-1)........... 24

PMBus Output Voltage Control (LTC3888-1) .......... 24

Soft-Start................................................................ 24

Time-Based Output Sequencing .............................25

Output Ramping Control.........................................25

Voltage-Based Output Sequencing .........................25

Output Disable........................................................25

Minimum Output Disable Times .........................26

Output Short Cycle .................................................26

Switching Frequency and Phase .............................26

PolyPhase Load Sharing.........................................27

Voltage Control Loop Compensation ......................27

Load Step Emulation...............................................27

Input Supply Monitoring.........................................27

Output Voltage Sensing and Monitoring .................28

Output Current Sensing and Monitoring .................28

Temperature Sense.................................................28

Resistor Configuration Pins....................................28

Internal EEPROM with CRC.....................................29

Fault Detection........................................................29

Input Supply Faults.............................................30

Hardwired PWM Response to Power

Stage Faults........................................................30

Hardwired PWM Response to Power Stage UV... 30

Hardwired PWM Response to VOUT Faults .........30

Power Good Indication .......................................31

Hardwired PWM Response to IOUT Faults ..........31

Hardwired PWM Response to Internal

Temperature Faults.............................................31

External Temperature Faults...............................31

Timing Faults......................................................31

External Faults....................................................32

Higher-Level Fault Handling ....................................32

Status Registers and ALERT Masking.....................32

FAULT Pin I/O..........................................................34

Fault Log Operation ................................................34

Fault Log Details.................................................35

Factory Default Operation.......................................38

PMBus Serial Interface ...........................................39

PMBus Serial Bus Addressing ............................43

PMBus Serial Bus Timeout.................................43

PMBus Communication Errors ...........................43

Serial Peripheral Interface (LTC3888 Only).............44

PMBus Command Summary ............................46

PMBus Commands.............................................46

Data Formats......................................................46

Applications Information ................................52

Efficiency Considerations .......................................52

Power Stage Selection and Interface ......................52

Using The VDR Monitor..........................................54

Unused TSNS Inputs ..............................................54

PWM Frequency and Inductor Selection.................54

CIN Selection...........................................................55

COUT Selection........................................................56

Programmable Loop Compensation .......................56

PCB Layout Considerations ....................................58

Output Voltage Sensing ..........................................59

Classical Analog Output Voltage Control

(LTC3888-1)............................................................59

PMBus Output Voltage Control...............................60

Using Output Voltage Servo....................................60

Soft-Start and Stop.................................................61

Time-Based Output Sequencing and Ramping .......61

Voltage-Based Output Sequencing .........................63

PWM Frequency Synchronization...........................64

PolyPhase Operation and Load Sharing..................64

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