DESCRIPTION
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 typical)
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 synchronous
rectification.
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.