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DC2583A (LT4294) does not supply enough power to the load

Category: Hardware
Product Number: LT4294

I've arranged the DC2583A (LT4294) and DC2660A as DCDC (LT8646S) boards as shown:

Then I've connected the SW-525 PoE switch + 48V/100W Power Supply and an electronic load for the LT8646S 5V output.

  • Jumper selection are set to JP11 and JP12 (40W PD Class 5)
  • PoE Auxiliary input is not used (left unnconnected)
  • LT4294 PWRGD is connected to LT8646S EN enable pin

The problem is I'm not able to get 5V@8A (40W) from the whole system as expected. In my case the maximum power I can deliver to the load is 22W. Why?

Any help from ADI support?


  • Can you measure the voltage or waveform of the /T2P pin? It sounds like your PoE switch is only allocating 25.5W of power to your PD. You can confirm the number of classification events by looking at the /T2P pin. If it is near zero volts, then the PSE is providing three or two classification events instead of four that indicates it has allocated 40W to this PD.

    Best Regards,


  • Hi Eric,

    Thank you for the tip. I was confused about the power budget of the SW-525 switch (90W) that it delivers to PD 25.5W on 'each port' in accordance with IEEE802.3at. To get a power delivered to PD of 40W I'll need a IEEE802.3bt PoE switch instead.


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