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LM51581: Sepic Controller Design for PoE-Application

Maik Halbe
Prodigy 150 points
Part Number: LM51581
Other Parts Discussed in Thread: LM5157, LM5158, LM5155

Hello,

I want to use the LM51581 as a sepic controller to get the poe-voltage of 54vdc. The parameters are V(in) = 20 - 60vdc; V(out) 54vdc, I(load) = 1.7A. (Second application with 3.0A then)

- I think the manual mentioned on page 36 is not ready yet or the link is wrong: Texas Instruments, LM5158Q1EVM-SEPIC User's Guide? Where do i get this manual?

- The excel calculator "LM5157-58_Excel_Quickstart_Calculator_for_Sepic_V1_0_1.xlsx" brings a red field / error if the input voltage is above 45vdc / V(supply)max, maybe this is because the voltage strength of the diode D1 (Diode, Schottky, 45 V, 10 A, AEC-Q101, CFP15)?

- Is their any more documentation i can use to realize the schematic?

Thanks for your help.

  • 0
    TI__Genius 11215 points

    Hello Malik, 

    Thanks for your message. You are right, the manual is not yet ready, thank you for pointing this out to us. The Excel calculator works for more than one device, maybe the suggested device is LM5157 due to the load current spec in your design, can you please check the cell at step 3: 



    The load current in your design is too high for the LM5158, due to this reason the Excel file suggested the LM5157. As the Vin is higher than the ABS MAX of the LM5157, you might step it down with a circuit similar to this one: 

    One example that you can consider, is the EVM of the LM5155 in SEPIC configuration:
    https://www.ti.com/lit/pdf/snvu628 

    This device is very similar to the LM5157/58, but it has an external MOSFFET in order to allow higher power. If you need 3A of load current in your second design, maybe you may consider to build your system directly with LM5155. 

    Let me know if further help is needed. 

    Kind regards, 

    EM 

  • 0 in reply to EM
    Prodigy 150 points

    Hello EM,

    i'm using the LM51581, so the input voltage is 3.2 to 60vdc. I understand the problem with the input voltage by using the excel calculation. With the LM5157 the input voltage range is smaller and the calculator use in this version only the part LM5157. Thanks for your help.

    Kind reagards

    Maik

  • +1 in reply to Maik Halbe
    TI__Guru 58641 points

    Hello Maik,

    I am not sure if you have an additional question.

    If you got all the required information, it would be great if you push the Solved button to close this thread.

    Best regards,

     Stefan