1
Rev. 0
DESCRIPTION
LT4293, LT4321
IEEE 802.3bt and LTPoE++
Interoperable Powered Device
Demonstration circuit 2911A is an IEEE 802.3bt compli-
ant and LTPoE++ interoperable Power over Ethernet (PoE)
Powered Device (PD). It features the
PD interface
PoE ideal diode bridge controller.
The LT4293 provides LTPoE++, IEEE 802.3af (PoE,
Type 1), IEEE 802.3at (PoE+, Type 2), and IEEE 802.3bt
(PoE++, Type 3 and 4) compliant interfacing. It utilizes an
external, low R
DS(ON)
(30mΩ typical) N-channel MOSFET
for the Hot Swap function to improve efficiency.
Power good (PWRGD) output indicates the PD control-
ler is ready to provide power to the downstream load.
This signal can be used to enable an isolated power sup-
ply. The
T2P
output indicates the available power from
the Power Sourcing Equipment (PSE). This signal
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PERFORMANCE SUMMARY
BOARD PHOTOS
communicates allocated power from either LTPoE++
or IEEE 802.3bt-compliant PSEs to the downstream
PD circuitry.
The LT4321 controls eight low R
DS(ON)
(57mΩ typical)
N-channel MOSFETs to further improve end-to-end power
delivery efficiency and ease thermal design. This solution
replaces the eight diodes typically found in a passive PoE
rectifier bridge.
The DC2911A accepts up to 90W of delivered power from
a PSE via the RJ45 connector (J1) or a local 48V DC
power supply using the auxiliary supply input. When both
supplies are connected, the auxiliary supply input has
priority over the PoE input.
Design files for this circuit board are available
Description
Performance Summary
Board Photos
Typical Performance Characteristics
Quick Start Procedure
Schematic Diagram
PARAMETER
CONDITIONS
VALUE
Port Voltage (V
PORT
)
At RJ45
37V to 57V
Auxiliary Voltage
From AUX+ to AUX– Terminals
37V to 57V
Efficiency
V
PORT
= 48V, I
OUT
= 1.5A
99.2% (Typical)
T2P
Switching Frequency
Connected to an IEEE 802.3bt or LTPoE++ PSE
That Allocates at Least 38.7W
840Hz (Typical)
Top Side
Bottom Side
