English
Language : 

LTC4268-1_12 Datasheet, PDF (1/46 Pages) Linear Technology – High Power PD With Synchronous No-Opto Flyback Controller
Features
n Robust 35W PD Front End
n IEEE 802.3af Compliant
n Rugged 750mA Power MOSFET With Precision Dual
Level Current Limit
n High Performance Synchronous Flyback Controller
n IEEE Isolation Obtained Without an Opto-Isolator
n Adjustable Frequency from 50kHz to 250kHz
n Tight Multi-Output Regulation With Load
Compensation
n Onboard 25k Signature Resistor
n Programmable Classification Current to 75mA
n Complete Thermal and Over-Current Protection
n Available in Compact 32-Pin 7mm × 4mm DFN
Package
Applications
n VoIP Phones With Advanced Display Options
n Dual-Radio Wireless Access Points
n PTZ Security Cameras
n RFID Readers
n Industrial Controls
n Magnetic Card Readers
n High Power PoE Systems
LTC4268-1
High Power PD With
Synchronous No-Opto
Flyback Controller
Description
The LTC®4268-1 is an integrated Powered Device (PD)
controller and switching regulator intended for IEEE 802.3af
and high power PoE applications up to 35W. By including
a precision dual current limit, the LTC4268-1 keeps inrush
below IEEE 802.3af current limit levels to ensure interop-
erability success while enabling high power applications
with a 750mA operational current limit.
The LTC4268-1 synchronous, current-mode, flyback
controller generates multiple supply rails in a single
conversion providing for the highest system efficiency
while maintaining tight regulation across all outputs. The
LTC4268-1 includes Linear Technology’s patented No-Opto
feedback topology to provide full IEEE 802.3af isolation
without the need of opto-isolator circuitry.
The oversized power path and high performance flyback
controller of the LTC4268-1 combine to make the ultimate
solution for power hungry PoE applications such as WAPs,
PTZ security cameras, RFID readers and ultra-efficient
802.3af applications running near the 12.95W limit.
The LTC4268-1 is available in a space saving 32-pin DFN
package.
L, LT, LTC, LTM and SwitcherCAD are registered trademarks and LTPoE++ and ThinSOT are
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners. Protected by U.S. Patents including 5841643.
Typical Application
35W High Efficiency PD Solution
–54V FROM
DATA PAIR
DF1501S
~+
~–
–54V FROM
SPARE PAIR
DF1501S
~+
~–
T1: PA1477NL
T2: PA0184
SMAJ58A
47k
100k
BAS21
20Ω
28.7k ≥5µF
T1 1%
3.01k
100pF •
+
T1
470µF
×4
56Ω
•
47Ω
B0540W
FMMT618
47µF
1%
Si4490DY
Si7336ADP
0.1µF
VPORTP PWRGD PWRGD UVLO ILIM_EN
VCC
FB PG SENSE+
SHDN
RCLASS
VPORTN
VNEG PGDLY
LTC4268-1
tON SYNC RCMP ENDLY
SENSE–
SG
VCMP
OSC GND SFST CCMP
RCLASS
12k 169k
100k
47pF
FMMT718
0.02Ω
15Ω
330Ω
0.1µF
10nF
20k
2.2nF
T2
••
10k
0.033µF
3.3V
1µF
BAT54
42681 TA01a
42681fc
1