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Using a PoE PSE to control a DC power line.

Category: Hardware
Product Number: LTC4279

Hello,

I'd like a bit of advice / recommendations for managing the output of a 48v DC supply:

  • The output will supply up to 10A of current to a servo motor driver and isolated DC:DC converter.
  • The powered device will be on the other end of a cable.
  • It's possible that the cable could be connected to lower voltage powered devices from other systems.

I think I need to do detection & classification, soft start, and disconnection detection.  My idea is to use a PoE PSE controller (such as LTC4279, LTC4274, LTC4291) to perform these tasks, modifying the sense resistor, MOSFET & output protection passives to suit the higher current.

At the PD end I envisage using a LT4321 & LT4293 with similarly uprated current capacity.

Has anyone done something like this before / sees potential problems of doing this way / can suggest a better solution?

Many thanks in advance for your ideas, guidance or solutions. 

  • Hello,

    Due to an issue with EZ I did not receive notifications for this post. My apologies. I understand this reply is likely too late to be useful for you. In case anyone else has a similar request, I will answer your question.

    An LTC4279/LT4293/LT4321 based system can be modified for higher power levels than PoE++ or LTPoE++, though I have not heard of a system targeting 500W / 10A. You can configure the LTC4279 for UltraPWR mode then ensure the LT4293 presents a valid detection and classification signature for a successful power on. My biggest concern with adjusting the sense resistor would be Classification and Inrush as both use the sense voltage. You will need a low RDSON MOSFET with high SOA for this application.

    Best Regards,

    Eric