LINEAR LTC4269 User's Manual

L DESIGN FEATURES

PD Controller ICs with Integrated Flyback or Forward Controllers Meet

Demands of 25.5W Po E+ by Ryan Huff

Introduction The IEEE 802.3af Power over Ether- to 25.5W. The new “at” standard, com- served by a synchronously rectified net (Po E) standard allows a powered monly referred to as Po E+, also adds (i.e. MOSFET rectified) flyback or a device (PD), such as an internet a “handshaking” communications forward power supply topology. protocol (IP) telephone, to draw up to requirement between PDs and power To meet the new performance 12.95W from an Ethernet cable. When sourcing equipment (PSEs), while al- requirements of Po E+, including the 802.3af standard was drafted, lowing backward compatibility with handshaking, Linear Technology offers 12.95W appeared sufficient to cover the legacy “af” standard. a new family of PD controller ICs that the immediately imaginable range of New power control ICs are required integrate a front-end PD controller with PD products (primarily IP phones). to take advantage of these expanded a high performance synchronously Of course, application developers requirements. The DC/DC conversion rectified flyback (LTC429-1) or a are always far more innovative than and control schemes used for legacy forward (LTC429-2) power supply standards committees anticipate, so “af” PDs are not optimized for the in- controller. new power-hungry applications for creased power capability and feature

Po E immediately started to appear, requirements of Po E+. For instance, Features

such as dual-radio IEEE 802.11a/g in both standards the 37V to 57V Po E Both parts combine a PD control- and 802.11n wireless access points, voltage is converted to lower voltages ler—which includes the handshaking security cameras with pan/tilt/zoom that digital circuitry can tolerate. circuitry, Hot Swap™ FET, and input motors, and color LCD IP video This DC/DC conversion is handled protection—with a DC/DC power phones. 12.95W was suddenly not in the lower power 12.95W standard supply controller. While the power enough. The IEEE committee re- with a conventionally rectified (i.e., supply sections of the two parts are sponded with the 802.3at standard, diode rectified) flyback converter. The very different, the PD controller in which raises the available PD power higher power 25.5W standard is better both is identical.

T1 PA2369NL

AUXILIARY

POWER 10µH 5V

VPORTP

DO1608C-103 5A+

BAS21 27.4k 22p F

PDZ36B 1µF

B1100 8 PLCS 383k

BSS63LT1 3.01k

–54V FROM

1% FDS2582

DATA PAIR S1B T2P

5.1Ω FDS8880

UVLO VCCT2P FB PG

SMAJ58A

SENSE+

VPORTP

33mΩ –54V FROM 1%

SPARE PAIR SENSE– MMBT3906 MMBT3904

LTC4269-1

RCLASS

SG 1µF 0.1µF 16V

VPORTN PGDLYVNEG t ON SYNC ENDLY OSC SFST CCMP GND VCMPRCMP

BAT54

PE-68386

Figure 1. LTC4269-1-based synchronous flyback converter

Linear Technology Magazine • September 2009