LTC4266 and POE specs info

Hi,

I am designing a carrier board with 16 POE PSE channels in addition with 4*4 ports marvell 88E1548 phy. For the moment, i don't know if the distant devices will draw more than 12.95W so i considered the LTC4266 POE+ PSE as a start.

I have read some of the specifications about POE, but i still don't get some of the features.

Let's assume that i want to give a certain margin to my PD device and i use a class 4 PD (LT4275B) . My questions are :

  • during the classification stage, does the PSE detects the signature of the PD by sending 25.5W to the device? (if yes, i will need a 400W or more power supply :/ )
  • if my device is not drawing more than 10W (during normal processing), will it still work efficiently?

Sorry for the silly questions, i'm not familiar with POE.

Thank you in advance.

Best regards,

John

Parents
  • As usual i answer my own questions when i decide to read the datasheet in details and not the scattered informations on google.

    But correct me if i am wrong :

    -I want to use a LTC4266 with a 54V/200W external power supply

    -The distant device (<12.95W) uses a LT4275 PD with the correct RCLASS for a class3 signature(802.3 af)

    -At start-up, the LTC4266 performs auto classification (AUTO pin = 3.3V) and detects a class 3 devices (p18 figure 13). The power injected for classification is around 30mA*30V = 900mW

    -When the 4 ports are classified, the LTC4266 outputs 54V on all of its outputs

    Simple as that?

Reply
  • As usual i answer my own questions when i decide to read the datasheet in details and not the scattered informations on google.

    But correct me if i am wrong :

    -I want to use a LTC4266 with a 54V/200W external power supply

    -The distant device (<12.95W) uses a LT4275 PD with the correct RCLASS for a class3 signature(802.3 af)

    -At start-up, the LTC4266 performs auto classification (AUTO pin = 3.3V) and detects a class 3 devices (p18 figure 13). The power injected for classification is around 30mA*30V = 900mW

    -When the 4 ports are classified, the LTC4266 outputs 54V on all of its outputs

    Simple as that?

Children