Demonstration circuit 2911A is an IEEE 802.3bt compliant and LTPoE++ interoperable Power over Ethernet (PoE) Powered Device (PD). It features the LT4293 PD interface controller and the LT4321 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 RDS(ON) (30mΩ typical) N-channel MOSFET for the Hot Swap function to improve efficiency.
Power good (PWRGD) output indicates the PD controller is ready to provide power to the downstream load. This signal can be used to enable an isolated power supply. The T2P output indicates the available power from the Power Sourcing Equipment (PSE). This signal communicates allocated power from either LTPoE++ or IEEE 802.3bt-compliant PSEs to the downstream PD circuitry.
The LT4321 controls eight low RDS(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.