LTC4278_12 Datasheet, PDF (1/42 Pages) Linear Technology – Synchronous No-Opto Flyback Controller

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) con-
troller 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-lead DFN
package.
L, LT, LTC, LTM, Linear Technology, SwitcherCAD and the Linear logo are registered
trademarks and Hot Swap 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 _{25W PD Solution with 12V Auxiliary}
+
AUXILIARY
SUPPLY
(10V TO 57V)
–
54V FROM ~ +
DATA PAIR _{~ –}
54V FROM
SPARE PAIR
~+
~–
PDS5100H
0.1µF
8.2µH
+
10µF
10µF
BSS63
294k
21.5k
1µF
TO MICRO
46.4k
CONTROLLER ^3.01k
UVLO PWRGD T2P
V_PORTP
FB
V_CC
PG SENSE⁺
SHDN
R_CLASS
24k
30.9Ω
V_PORTN
LTC4278
SENSE^–
SG
V_CMP
V_NEG SYNC GND OSC PGDLY t_ON ENDLY R_CMP C_CMP
B1100
12k
33pF
100k 38.3k 1.8k
0.1µF
EPC3472G-LF
•
••
0.18µH
47µF +
5V
4.5A
100µF
FDMS2572
12mΩ
HAT2169
1µF
2.2nF
••
4278 TA01a
4278fc
1