LTC4268-1
High Power PD with
Synchronous NoOpto
Flyback Controller
FEATURES
DESCRIPTION
The LTC®4268-1 is an integrated Powered Device (PD)
controllerandswitchingregulatorintendedforIEEE802.3af
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.
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Robust 35W PD Front End
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IEEE 8X02.3af Compliant
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Rugged 750mA Power MOSFET with Precision Dual
Level Current Limit
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High Performance Synchronous Flyback Controller
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IEEE Isolation Obtained without an Optoisolator
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Adjustable Frequency from 50kHz to 250kHz
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Tight Multi-Output Regulation with Load
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
LTC4268-1includesLinearTechnology’spatentedNoOpto
feedback topology to provide full IEEE 802.3af isolation
without the need of optoisolator circuitry.
Compensation
Onboard 25k Signature Resistor
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Programmable Classification Current to 75mA
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Complete Thermal and Over-Current Protection
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Available in Compact 32-Pin 7mm × 4mm DFN
Package
APPLICATIONS
The oversized power path and high performance flyback
controller of the LTC4268-1 combine to make the ultimate
solutionforpowerhungryPoEapplicationssuchasWAPs,
PTZ security cameras, RFID readers and ultra-efficient
802.3af applications running near the 12.95W limit.
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VoIP Phones with Advanced Display Options
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Dual-Radio Wireless Access Points
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PTZ Security Cameras
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RFID Readers
Industrial Controls
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The LTC4268-1 is available in a space saving 32-pin DFN
package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5841643.
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Magnetic Card Readers
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High Power PoE Systems
TYPICAL APPLICATION
35W High Efficiency PD Solution
3.3V
+
+
470μF
×4
•
≥5μF
100pF
56Ω
28.7k
1%
BAS21
20Ω
T1
47k
47Ω
•
T1
SMAJ58A
100k
B0540W
•
3.01k
1%
DF1501S
FMMT618
47μF
Si4490DY
Si7336ADP
~ +
–54V FROM
DATA PAIR
~ –
FMMT718
0.1μF
+
V
PWRGD PWRGD UVLO I
V
CC
FB PG
SENSE
PORTP
LIM_EN
DF1501S
~ +
~ –
1μF
0.02Ω
330Ω
SHDN
–54V FROM
SPARE PAIR
–
SENSE
15Ω
LTC4268-1
R
CLASS
SG
2.2nF
0.1μF
10nF
20k
V
CMP
T2
V
V
NEG
PGDLY
t
SYNC
R
ENDLY
OSC GND SFST C
CMP
PORTN
ON
CMP
•
•
R
10k
12k
169k
100k
47pF
CLASS
BAT54
T1: PA1477NL
T2: PA0184
42681 TA01a
0.033μF
42681fa
1