LTC4278 Datasheet, PDF (1/40 Pages) Linear Technology – IEEE 802.3at PD with Synchronous No-Opto Flyback Controller and 12V Aux Support

LTC4278
FEATURES
IEEE 802.3at PD with
Synchronous No-Opto Flyback
Controller and 12V Aux Support
DESCRIPTION
n _{25.5W IEEE 802.3at Compliant (Type 2) PD}
n _{10V to 57V Auxiliary Power Input}
n _{Shutdown Pin for Flexible Auxiliary Power Support}
n _{Integrated State-of-the-Art No-Opto Synchronous}
Flyback Controller
– Isolated Power Supply Efficiency >92%
– 88% Efficiency Including Diode Bridge and
Hot Swap™ FET
n _{Superior EMI Performance}
n _{Robust 100V 0.7Ω (Typ) Integrated Hot Swap MOSFET}
n _{IEEE 802.3at High Power Available Indicator}
n _{Integrated Signature Resistor and Programmable}
Class Current
n _{Undervoltage, Overvoltage and Thermal Protection}
n _{Short-Circuit Protection with Auto-Restart}
n _{Programmable Soft-Start and Switching Frequency}
n _{Complementary Power Good Indicators}
n _{Thermally Enhanced 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}
The LTC^®4278 is an integrated Powered Device (PD)
controller and switching regulator intended for high power
IEEE 802.3at and 802.3af applications. With a wide input
voltage range, the LTC4278 is specifically designed to sup-
port PD applications that include a low-voltage auxiliary
power input such as a 12V wall adaptor. The inclusion of
a shutdown pin provides simple implementation of both
PoE and auxiliary dominate applications. In addition, the
LTC4278 supports both 1-event and 2-event classifications
as defined by the IEEE, thereby allowing the use in a wide
range of product configurations.
The LTC4278 synchronous, current mode, flyback control-
ler generates multiple supply rails in a single conversion
step providing for the highest system efficiency while main-
taining tight regulation across all outputs. The LTC4278
includes Linear Technology’s patented No-Opto feedback
topology to provide full IEEE 802.3 isolation without the
need of an opto-isolator circuit. A true soft-start function
allows graceful ramp-up of all output voltages.
The LTC4278 is available in a space saving 32-pin DFN
package.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5841643.
TYPICAL APPLICATION _{25W PD Solution with 12V Auxiliary}
+
AUXILIARY
SUPPLY
(10V TO 57V)
–
54V FROM ~ +
DATA PAIR _{~ –}
54V FROM
SPARE PAIR
~+
~–
2.2μH
+
100k
10μF
10μF
680k
PDS5100H
0.1μF
BSS63LT1 294k
41.2k
21.5k
TO MICRO
CONTROLLER ^3.01k
UVLO PWRGD T2P
FB
V_PORTP
SHDN
R_CLASS
24k
30.9Ω
LTC4278
V_PORTN
V_NEG SYNC GND OSC PGDLY t_ON
1μF
V_CC
PG SENSE⁺
SENSE^–
ENDLY
R_CMP
SG
V_CMP
C_CMP
10k
33pF
100k 38.3k 1.8k
0.1μF
EPC3472G-LF
•
••
0.18μH
47μF +
5V
5A
100μF
FDMS2572
12mΩ
HAT2169
1μF
2.2nF
••
4278 TA01a
4278f
1