LTC4268-1 Datasheet, PDF (1/48 Pages) Linear Technology – High Power PD with Synchronous NoOpto Flyback Controller

FEATURES
n _{Robust 35W PD Front End}
n _{IEEE 8X02.3af Compliant}
n _{Rugged 750mA Power MOSFET with Precision Dual}
Level Current Limit
n _{High Performance Synchronous Flyback Controller}
n _{IEEE Isolation Obtained without an Optoisolator}
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 NoOpto
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 NoOpto
feedback topology to provide full IEEE 802.3af isolation
without the need of optoisolator 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.
, 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.
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
≥5μF
28.7k
T1 ^1%
3.01k
100pF ^•
56Ω
+
T1
•
470μF
×4
47Ω
B0540W
FMMT618
47μF
1%
Si4490DY
Si7336ADP
0.1μF
V_PORTP PWRGD PWRGD UVLO I_{LIM_EN}
V_CC
FB PG SENSE⁺
SHDN
R_CLASS
LTC4268-1
SENSE^–
SG
V_PORTN
V_NEG PGDLY
V_CMP
t_ON SYNC R_CMP ENDLY OSC GND SFST C_CMP
R_CLASS
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
42681fa
1