ADP1821

Rev. B | Page 2 of 24

TABLE OF CONTENTS

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

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

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

Revision History ............................................................................... 2

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

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

ESD Caution.................................................................................. 5

Simplified Block Diagram ........................................................... 5

Pin Configuration and Function Descriptions............................. 6

Typical Performance Characteristics ............................................. 7

Theory of Operation ........................................................................ 9

Soft Start ........................................................................................ 9

Error Amplifier ............................................................................. 9

Current-Limit Scheme................................................................. 9

MOSFET Drivers........................................................................ 10

Input Voltage Range ................................................................... 10

Setting the Output Voltage ........................................................ 10

Switching Frequency Control and Synchronization.............. 10

Compensation............................................................................. 11

Power-Good Indicator ............................................................... 11

Thermal Shutdown .................................................................... 11

Shutdown Control...................................................................... 11

Application Information................................................................ 12

Selecting the Input Capacitor ................................................... 12

Output LC Filter ......................................................................... 12

Selecting the MOSFETs ............................................................. 13

Setting the Current Limit .......................................................... 14

Feedback Voltage Divider ......................................................... 14

Compensating the Voltage Mode Buck Regulator................. 14

Setting the Soft Start Period...................................................... 18

PCB Layout Guideline ................................................................... 19

Recommended Component Manufacturers........................... 20

Application Circuits ....................................................................... 21

Summary of Equations .................................................................. 23

Compensation Equations .......................................................... 23

Type II Compensation Equations ............................................ 23

Type III Compensation Equations........................................... 23

Outline Dimensions ....................................................................... 24

Ordering Guide .......................................................................... 24

REVISION HISTORY

12/06—Rev. A to Rev. B

Updated Format..................................................................Universal

Changes to Features Section............................................................ 1

Changes to Applications Section .................................................... 1

Changes to General Description Section ...................................... 1

Changes to Error Amplifier............................................................. 3

Changes to PWM Controller .......................................................... 3

Changes to Oscillator Frequency.................................................... 3

Changes to Theory of Operation Section...................................... 9

Changes to Application Information Section ............................. 12

Added PCB Layout Section ........................................................... 19

Changes to Application Circuits Section..................................... 21

Added Summary of Equations Section........................................ 23

1/06—Rev. 0 to Rev. A

Changes to Specifications Table ......................................................3

Changes to Theory of Operation Section.................................... 10

Changes to Input Voltage Range Section .................................... 11

Added Equation 1........................................................................... 12

Changes to Equation 7 and Equation 8 ....................................... 13

Added Equation 9........................................................................... 13

Changes to Equation 16................................................................. 14

Changes to Figure 15...................................................................... 14

Changes to Equation 21................................................................. 15

Changes to Figure 16...................................................................... 15

Changes to Equation 28................................................................. 15

Updated Outline Dimensions....................................................... 18

7/05—Revision 0: Initial Version