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LM5118: Output power too low

Lucas Bagrowski
Prodigy 120 points
Part Number: LM5118

Hello everybody,

I need some help for the LM5118. Thanks to WEBENCH Designer I made a circuit board including this component (my exact reference is LM5118MHX/NOPB) in order to convert every voltage between +7V and +25V into a +24V output, 1.5A maximum. So the given circuit was :

(I didn't change the title of it but below you can read the real wanted specifications)

I designed my board using the components values on the scheme, I changed some Diodes and others but I respected the requirements. My issue appeared when I tested the board, I have +24,3V without load but when I connect the output to a variable resistor to simulate a consumption of 750 mA, the voltage drops at something like Vinput - 1V, here it was about +14V.

Can you help me with that please ?

Thanks

Lucas

  • 0
    TI__Guru 61355 points

    Hello Lucas,

    Do you have a schematic, layout and possibly a picture of your board to share?

    Please review the input voltage, output voltage and switch nodes at the same time. In addition, the feedback voltage would be interesting to see.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 120 points

    Hello Brigitte,

    Yes I have all this, I made my design on Kicad 6 for information.

    I write here the references of interesting components:

    D201: CDBC540-G

    D202: SS1P4LHM3/85A

    L201: SRP7050AA-220M

    FET201: PJA3404_R1_00001

    FET202: PJA3404_R1_00001

    Here is my circuit board:

    And here the 3D Visualisation without components:

    Today I was working on this issue and I took some measurement with 3 differents Power Resistors connected to it, I supplied the system with voltages from +7,5V to +22,5V, I give it to you like that because I haven't yet exploited the values:

    I continue to work on it tell me if something could help you.

    Thanks for your time

    Best regards

    Lucas

  • 0 in reply to Lucas Bagrowski
    Prodigy 120 points

    Hello, I was verifying my design and I saw on WEBENCH that we can create custom parts for certains components, so that's what I did. And I learnt that my inductor is not well choosed : 

    I will try an other one.

    Best regards 

    Lucas

  • 0 in reply to Lucas Bagrowski
    TI__Guru 61355 points

    Hello Lucas,

    You can as well check out the quick start calculator which helps checking different components without recalculating the rest of the design: https://www.ti.com/lit/zip/snvu065

    The result might differ slightly from Webench, but both are just starting points. For final decisions, checks in the lab are absolutely necessary.

    BTW, I would recommend reviewing the EVM layout or even checking out your circuit on the EVM.

    Best regards,
    Brigitte