Passive POE buck converter

[midea_iot]

Hello,
I have been working on my POE project, and have found an almost suitable sollution. I am basing my design on the one found here. I have remade the design with components found at JLCPCB, however upon reading further it states, that this is designed for a 12-24V in and 5V 1.5A out use case. My use case is 48V in and 5V 2-3A out. My question is, can I just replace the SY8291 buck converter for one which has a higher input voltage and output current, or is this design not suitable in a passive 48V poe scenario?

--- Updated Oct 21, 2022 ---

For example, would this converter be a suitable replacement? SY8502FCC

 

[barry]

I don’t know about the converter, but I don’t think CAT5 cable is going to handle 3 amps.

 

[BradtheRad]

Stepping down 48 V to 5 V your prospective duty cycle is around 15 percent. During those times the converter draws (or tries to draw) over 4 Amperes. This is unlikely to achieve given Cat5 wires.

Besides which other wires inside the cable might pick up unwanted noise due to several Amperes going through a neighboring wire.

However you might get your desired power by drawing a fraction of an Amp continuously. This is the rating for POE, about 350 mA, or 15W. Your schematic includes C23 which serves to smooth the incoming current waveform to some extent. It may not be sufficient, and you may need to contrive additional input filtering.

 

[KlausST]

Hi,

I guess I miss something.
5V 3A makes 15W.
15W from 48V just gives about 350mA.

Just replacing the controller IC won`t work.
You need to design the new circuit with the information from the datasheet.

Klaus