1

Rev C

DEMO MANUAL

DC2475A-A

DESCRIPTION

LT4295, LT4321

High Efficiency IEEE802.3bt (PoE++, Type 3,

40W) PD with PoE Ideal Diode Bridge

Demonstration circuit 2475A-A is an Ethernet Alliance™

certified IEEE802.3bt compliant Power over Ethernet (PoE)

powered device (PD). It features the LT®4295 PD interface

and switching regulator controller with the LT4321 PoE

ideal diode bridge controller.

The LT4295 provides IEEE802.3af (PoE, Type 1),

IEEE802.3at (PoE+, Type 2), and IEEE802.3bt (PoE++,

Type 3 and 4) compliant interfacing and power supply

control. It utilizes an external, low RDS(ON) (57mΩ typi-

cal) N-channel FET for the Hot Swap function to improve

efficiency. The LT4295 controls a DC/DC converter that

utilizes a highly efficient flyback topology with synchro-

nous rectification.

PERFORMANCE SUMMARY

BOARD PHOTO

The LT4321 controls eight low RDS(ON) (57mΩ typical)

N-channel FETs 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 DC2475A-A accepts up to 40W of delivered power

from a power sourcing equipment (PSE) via the RJ45

connector (J1) or a local 48VDC power supply using the

auxiliary supply input. When both supplies are connected,

the auxiliary supply input has priority over the PoE input.

The DC2475A-A supplies a 12V output at up to 3A.

Design files for this circuit board are available.

Top Side

PARAMETER

CONDITIONS

VALUE

Port Voltage (VPORT)

At RJ45

37V to 57V

Auxiliary Voltage

From AUX+ to AUX– Terminals

37V to 57V

Output Voltage (VOUT)

12V (Typical)

Output Current (IOUT)

3A (Max)

Output Voltage Ripple

VPORT = 44V, IOUT = 3A

85mVP-P (Typical)

Load Regulation

±0.1% (Typical)

Efficiency

VPORT = 50V, IOUT = 3A, End-to-End

92% (Typical)

Switching Frequency

250kHz (Typical)

Bottom Side

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