AS1124

Akros Silicon, Inc.

6399 San Ignacio Avenue, Suite 250, San Jose, CA 95119 USA

408.746.9000



www.AkrosSilicon.com

GENERAL DESCRIPTION........................................................................................................................................................... 1

TYPICAL APPLICATIONS ........................................................................................................................................................... 1

FEATURES .................................................................................................................................................................................. 1

EXAMPLE APPLICATION............................................................................................................................................................ 1

APPLICATION DIAGRAM FOR A POE PD (FLYBACK CONVERTER) ...................................................................................... 1

FIGURES ..................................................................................................................................................................................... 3

TABLES ....................................................................................................................................................................................... 3

PIN DIAGRAM ............................................................................................................................................................................. 4

TYPICAL PERFORMANCE CHARACTERISTICS....................................................................................................................... 7

FUNCTIONAL DESCRIPTION................................................................................................................................................... 10

OVERVIEW OF POE .................................................................................................................................................................10

AS1124 POE DESIGN ...............................................................................................................................................................10

POWER FEED ALTERNATIVES FOR 10/100 SYSTEMS......................................................................................................... 11

AS1124 OVERVIEW .................................................................................................................................................................. 12

RECTIFICATION & PROTECTION ............................................................................................................................................ 12

PD CONTROLLER.....................................................................................................................................................................12

MODES OF OPERATION ..........................................................................................................................................................12

RESET .......................................................................................................................................................................................12

SIGNATURE DETECTION MODE .............................................................................................................................................12

CLASSIFICATION MODE ..........................................................................................................................................................12

LOCAL POWER MODE .............................................................................................................................................................13

IDLE MODE ...............................................................................................................................................................................13

ON STATE .................................................................................................................................................................................13

PD CONTROL POWER AND THERMAL PROTECTIONS........................................................................................................ 13

UNDER VOLTAGE LOCKOUT (UVLO) .....................................................................................................................................13

CURRENT LIMIT/CURRENT SENSE ........................................................................................................................................13

THERMAL LIMIT PROTECTION................................................................................................................................................13

POE POWER-ON STARTUP WAVEFORM............................................................................................................................... 14

DC-DC CONTROLLER .............................................................................................................................................................. 15

OVERVIEW................................................................................................................................................................................15

CURRENT-LIMIT/CURRENT SENSE........................................................................................................................................15

LOW LOAD CURRENT OPERATION........................................................................................................................................15

COMPENSATION AND FEEDBACK .........................................................................................................................................15

SOFT-START INRUSH CURRENT LIMIT .................................................................................................................................15

AUXILIARY POWER OPTION ................................................................................................................................................... 15

DC-DC CONVERTER TOPOLOGIES........................................................................................................................................ 15

FLYBACK VS. FORWARD OPERATION...................................................................................................................................15

BUCK OPERATION ...................................................................................................................................................................15

PRIMARY SWITCHING TOPOLOGY ........................................................................................................................................15

THERMAL DE-RATING AND BOARD LAYOUT CONSIDERATIONS.......................................................................................16

AS1124 PCB FOOTPRINT ........................................................................................................................................................ 16

APPLICATION CIRCUITS.......................................................................................................................................................... 17

PHYSICAL DIMENSIONS.......................................................................................................................................................... 19

CONTACT INFORMATION........................................................................................................................................................20

IMPORTANT NOTICES .............................................................................................................................................................20

LEGAL NOTICE .........................................................................................................................................................................20