I am using the SI3402 chip to use POE.
But it does not work properly.
The circuit I have constructed is as follows.
POE: SI3402 (non-isolated)
Ethernet Transceiver: H2019NL
When POE cable is plugged in, it charges for the first time but it becomes impossible to charge soon. I think that the POE side circuit is a problem because I operate normally when only 5V is applied to the charge IC.
Since it is confirmed that 5V is output from the output terminal, it is not a voltage problem.
I attach the schematic that I composed with PDF.
Please make sure that there is something strange in my circuit.
to localize the problem, please try to replace your PSE (power sourcing equipment) with laboratory supply, provide 50V from the lab supply.
Disconnect you application from the output of the Si3402 circuit.
Instead of you application, connect an electronic load, or a simple power resistor and try to load the output of your Si3402 circuit.
What is the power need for your application? (the buck configuration at 5V output is capable to provide up to 7W)
Do you have any earth ground connection in your application (such as USB)? The buck topology does not provide isolation, therefore it is not possible to use USB or any other connectors which are earth grounded.
Thanks and regards,
R5/R6 in your schematic indicate a 1.32VDC output, but your flyback is a 1:1, so the PWM is likely going to be having a tough time, or is this an error? For a class 3 PD (based on your R24 value the Si3402B requires at least one of the CT and SP pins to be powered by the PSE lines, but looking at your RJ jack part, I don't know if it will work because normally the CT and SP pins would be biased a diode drop higher than the bridge output. – isdi 10 hours ago
Carefully read AN956 and the Si3402BISO-EVB documents before making changes to the design like this, it's easy to miss critical stuff. Also make sure your PCB layout meets their thermal resistance guidelines and that the thermal pad is connected to the proper netlist node.