Hi, I am working design an LTPoE++ PD which require 90W power. I am using LT4275 as PD controller, Normal bridge, with a controller. The goal is making an led driver powered by PoE. Even though the circuit is designed for LTPoE++ standards, power will shut down after 30W. Checked the waveform, looks like it is working with type-2. I can`t drive led of 36V,1A with this at maximum output. Pse got shutting down around 0.8A(voltage around 36V). Even though Rcls(49.9ohm) and Rcls++ (118ohm) selected correctly, it is not providing sufficient output.PSE using is capable of providing up to 60W. Attached the circuit diagram. Designed based on the DC2125 circuit diagram. Please give us some suggestions to rectify the same.
Note:R51 (value=10K) not connected in actual).
Detect and class signaling waveform:
This sounds like a problem with your PSE or PoE injector. Can you provide more information about what you are using to provide power? As you mentioned about your classification waveform, this is a Type 2 negotiation for 25.5W. To account for worst case cable drop, a Type 2 PSE will output 30W max. This PSE does not appear to be LTPoE++ compliant or have LTPoE++ enabled. Even if this PSE claims it can provide 60W of power it does not look like it's allocating 60W. More information about the PSE is required to be sure.
I have some notes about your schematic as well. PWRGD should be used to enabled the downstream load. Q1, PSMN2R8-25MLC is rated for 25V. This part should not be used in PoE as 37V - 57V is the common operating range, with surges to 90V possible. I recommend the PSMN040-100MSE or PSMN075-100MSE, or another 100V MOSFET with sufficient SOA. /T2P indicates PSE power allocation, and should be monitored in an IEEE compliant system.
Thank you so much for your suggestions. I will try to improve the same. We tested with pse mentioned below:
Can somebody recommend a linear pse demo board (single port even enough ) but should capable of delivering power 90W, so that I can test my PD-4275A design.
The cheapest demo board is recommended. Single output(or 1-4) port is enough for testing.
Check out LTC4279, Single Port PoE/PoE+/LTPoE++ PSE Controller. DC2541A supports up to 90W LTPoE++ PDs.