• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 631 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS23755: Design example discrepancy: maximum output power / efficiency

Nicholas Carley
Genius 9925 points
Part Number: TPS23755

In the design example given on the datasheet it specifics an output power of 12W: 

At full load the efficiency is called out as 87%. This means 12W/0.87 = 13.8W needed at the input. Doesn't this exceed the power classification? Looks like the maximum allowed power at the input is 12.95W? 

Can you please help clarify this?

  • 0
    TI__Mastermind 21320 points

    Hello Nicholas,

    Thank you for your question. So something important to understand is the PoE specification, and the specs we design our power converters to. These two are not always the same. In this case, they differ. 

    The PoE spec is as table 2 says, about 13W. If you wanted to stay within this spec, you could not use 1A load. The maximum load would instead be about 0.94A. The max output power is 87% of 13W = 11.31W. So to use 12V at 1A load would exceed the spec. 

    However, when we decided to design the power converter, we did not design for 0.94A, but 1A. This was done for ease of design and to encompass a larger use case. Therefore, if a power adapter was used as the input that could supply more power so 12V-1A output is possible, this part's power converter could still be used. It would be out of PoE spec, but in this case the power is not coming from a PoE standard PSE.

    Does that make sense? Let me know if I caan clarify anything for you!

    Regards,

    Michael Pahl