LT4276_15 Datasheet, PDF (1/26 Pages) Linear Technology – LTPoE/PoE/PoE PD Forward/Flyback Controller

LT4276
LTPoE++/PoE+/PoE
PD Forward/Flyback Controller
Features
n _{IEEE802.3af/at and LTPoE++}^™ _{90W Powered Device}
(PD) with Forward/Flyback Controller
n _{LT4276A Supports All of the Following Standards:}
n _{LTPoE++ 38.7W, 52.7W, 70W and 90W}
n _{IEEE 802.3at 25.5W Compliant}
n _{IEEE 802.3af up to 13W Compliant}
n _{LT4276B is IEEE 802.3at/af Compliant}
n _{LT4276C is IEEE 802.3af Compliant}
n _{Superior Surge Protection (100V Absolute Maximum)}
n _{Wide Junction Temperature Range (–40°C to 125°C)}
n _{Auxiliary Power Support as Low as 9V}
n _{No Opto-Isolator Required for Flyback Operation}
n _{External Hot Swap}^™ _{N-Channel MOSFET for Lowest}
Power Dissipation and Highest System Efficiency
n _{>94% End-to-End Efficiency with LT4321 Ideal Bridge}
n _{Available in a 28-Lead 4mm × 5mm QFN Package}
Applications
n _{High Power Wireless Data Systems}
n _{Outdoor Security Camera Equipment}
n _{Commercial and Public Information Displays}
n _{High Temperature Applications}
Description
The LT^®4276 is a pin-for-pin compatible family of IEEE
802.3 and LTPoE++ Powered Device (PD) controllers. It
includes an isolated switching regulator controller capable
of synchronous operation in both forward and flyback
topologies with auxiliary power support.
The LT4276A employs the LTPoE++ classification scheme,
receiving 38.7W, 52.7W, 70W or 90W of power at the PD
RJ45 connector, and is backwards compatible with IEEE
802.3. The LT4276B is a fully 802.3at compliant, 25.5W
Type 2 (PoE+) PD. The LT4276C is a fully 802.3af compli-
ant, 13W Type 1 (PoE) PD.
The LT4276 supports both forward and flyback power
supply topologies, configurable for a wide range of PoE
applications. The flyback topology supports No-Opto
feedback. Auxiliary input voltage can be accurately sensed
with just a resistor divider connected to the AUX pin.
The LT4276 utilizes an external, low R_DS(ON) N-channel
MOSFET for the Hot Swap function, maximizing power
delivery and efficiency, reducing heat dissipation, and
easing the thermal design.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
LTPoE++, and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Typical Application
+
AUX
37V-57V _–
LTPoE++ 70W Power Supply in a Forward Mode
+
V_PORT
–
0.1µF
3.3k
10nF
FMMT723
100µH
10µF
••
22µF
VPORT HS V_IN HS SW
GATE
SRC V_CC
AUX
LT4276A
R_CLASS
R_CLASS++
GND FB31 SS ROSC
V_CC FFS PG
DLY _ISEN+
V_CC
ISEN–
20mΩ
SG
0.1µF
T2P
ITHB
4276 TA01
10k
100pF
100k
OPTO
TO MICROPROCESSOR
For more information www.linear.com/LT4276
+
+ _5V
13A
–
LT4276 Family
LT4276
MAX DELIVERED ^GRADE
POWER
ABC
LTPoE++ 90W l
LTPoE++ 70W l
LTPoE++ 52.7W l
LTPoE++ 38.7W l
25.5W
ll
13W
lll
4276f
1