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TPS2372: Output falls after connecting some loads.

Part Number: TPS2372

Hello, I'm using the TPS2372-4RGWR, and when I first plugged the ethernet cable (no loads), it made the whole process of detection, classification and power correctly. After that, I tried to connect 1 24V Led bar and it was okay, but when I tried to connect the third one, the power falls and it's not able to supply sufficient power.

Im using autocls in the TPS, and I have checked the possible differences between my schematic, and the schematic of the TPS2372-3EVM-757 board, which seems to be similar. Here is my PoE design, with a 24V regulator at the output of the TPS:

The TPS2372-3EVM-757 schematic is this:


The waveform I get when te power falls is the following:

After 130 ms, the power in the TPS falls.

Can anybody help me with this?

Thank you so much,


  • Hello, 

    Turn off Auto Class. 

    Auto Class is a feature that will draw the maximum power immediately after power up to tell the PSE exactly how much power it needs so that the PSE can allocate a very specific amount of power to that particular PD. 

    This is very useful if you have an array of LED's across a factory floor. Maybe some LED"s are closer to the PSE, and can use shorter cables. The thing about LED loads is once they are turned on, they do not change -- they are not dynamic like a camera that has motors and features turning on and off. Therefore, autoclass can optimize power in an LED grid. 

    When auto class is used and LED's are added after power up, the load is changing, which is what we told the PSE we would not do. I would suggest turning it off. It's definitely a feature that is specifically made for this application, but that is not obvious in any documentation. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.




    Michael P.

    Applications Engineer

    Texas Instruments 

  • Hello Michael. Thank you very much!

    That improved the system so I was able to connect 2 more LEDs, the problem is that when I connect any other LED bar, the TPS2372 overheats and the output falls again. Can this be due to my DC/DC regulator?


  • I have already solved the problem. The first problem was using the Auto Class, as Michael said. The other problem was that I removed the conection between the PG pin and the enable of my DC/DC converter so it was enabled since the start. Connecting the enable to the PG solved the second issue.