why need 54.5-57V not 48V input for POE++
what's the Ilim for POE++
Please clarify what you are referring to with PoE++. The terms PoE, PoE+ and PoE++ are generic and do not specifically apply to a standard. PoE++ is typically used as a term for PoE power levels higher than IEEE 802.3at Type 2 power (25.5W). Linear Technology's proprietary LTPoE++ is an example which provides power levels of 38.7W, 52.7W, 70W and 90W at the PD input.
1) Increasing the minimum voltage requirements is one way to increases the power delivered to the PD.
2) What are the power levels that you are asking the Ilim on?
1) So,I can believe that the minimum voltage requirements only affect the power for PD but not the function of POE?
And there is another question.
The PHY of PD is always damaged during hot plug of the network cable,though with much protection. Have you solutions?
1) The minimum voltages you listed previously would not affect IEEE detection and classification functions for ADI/LTC PSE controllers. The port output voltage has an affect on the delivered power to the PD.
2) What ADI/LTC PoE controllers are you using?
What is the PD and what is it connected to? Make sure the PD is connected to an IEEE 802.3af/at/bt or LTPoE++ compliant PSE. Make sure the PHY of the PD is isolated from PoE.
2) use LTC4266A4 for PSE, LTC4275A for PD. Datasheet for LTC4266A does not mention the Ilimit for 90W
3) PD uses LTC4275A and LT4321 as development board connected with LTPoE++.PHY on PD is isolated from PoE through the network transformer which is recommended by the development board
We test EFT( Electrical Fast Transient / Burst IEC 61000-4-4) ,failed at level 2 because of network timeout. Is there any solution?
2) The current limits for LTPoE++ are set to insure that at the minimum PSE supply voltage the PSE will deliver on all four Ethernet pairs the specific LTPoE++ power level at the PD input after a 100m CAT5e Ethernet cable.
3a) It was mentioned earlier the PD was hot plugged. If connected to the LTC4266A, an LTPoE++ PSE will probe at a safe low voltage and current for a valid signature resistance. There should not be a live high voltage at the cable. Only when after valid signature has been detect the PSE turn on the full voltage.
3b) Also, the LT4275A is a PD interface only. Make sure the downstream power at the LT4275A hot swap output maintains isolation such connecting to an isolated DC/DC converter.
4) With limited information on what you provided me, my best recommendation is to follow the LT4275A datasheet for protection components, capacitance and gate drive.