LTC4263 - 1000Mbps Design

Question

Hello, 
 We have a device in our product that can be powered over PoE with 1000Mbps of data flow and are looking into a PSE controller that can do it. 
 The LTC4263 looked very interesting and might be a solution, but I'm not quite sure on how or if this is the correct part for implementation (if it should be a different part then if a suggestion could be made that would be great). I do have a couple questions regarding this: 
 1. This sounds like a general question, but can PoE still negotiate and operate at 24V? I want to avoid using a DC/DC regulator to bump it to 48V. Not sure if a PoE injector IC of sorts is needed here. 2. If I was to implement this with 1000Mbps data speeds (using all 8 pairs), which center taps would power need to be connected to? As I understand, it would be between CT of pairs 1&2 and 7&8. In the same respect, we would be using a custom connector where we expect power to flow with data and would be provided on a separated contact point. 3. Is the evaluation board for this chip only compatible for 100Mbps devices as power flows through the spare pins? 
 Any help on any of those questions and/or links to where the answers may lie would be greatly appreciated! 
 Kind Regards, Neehar

dreyeslt · Accepted Answer

The LTC4263 is an IEEE 802.3af compliant PSE controller. This standard defines PSE output power up to 15.4W and an output voltage of 44V to 57V. For the next level of higher power, 30W, consider an 802.3at compliant PSE controller such as the LTC4279. 
 IEEE specified PoE PSEs will not operate down at 24V. 
 The LTC4263 may be used with 1000Mbps data (1000BASE-T) which has data transformers on all 4 pairs. At the time of release of the LTC4263, 1000Mbps was not a popular application. Power applied at a data pairset is to go through the Ethernet transformer center taps. For connections consider the following: 
 - An 802.3af PSE pinout may be either on Alternative A (pairs 1/2 and 3/6) or Alternative B (pairs 4/5 and 7/8). 
 - An Endpoint PSE may implement Alternative A or B. A Midspan PSE can implement Alternative B only. 
 - Alternative A, MDI-X connection is Negative on pair 1/2, Positive on pair 3/6. Alternative A, MDI connection is Positive on pair 1/2, Negative on pair 3/6. Alternative B for all is Positive on pair 4/5, Negative on pair 7/8. 
 The LTC4263 is setup for 10/100BASE-T but as mentioned earlier may be used in 1000BASE-T applications. Refer to the LTC4279 datasheet and demo board for examples on how to connect PoE to a 1000BASE-T system.)

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LTC4263 - 1000Mbps Design