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WEBENCH® Tools/LM5022-Q1: Datasheet and webench discrepancy

Joel Ramos
Prodigy 120 points
Part Number: LM5022-Q1

Tool/software: WEBENCH® Design Tools

Hello,

I am designing a boost converter to take 42v IN to 90v OUT @ 5A. I used both WEBENCH and the application notes from the datasheet and I'm having trouble with some components.

1) Rsns value is different between the calculation and WEBENCH. If I do the calculation with the components following the application notes, I get a shunt resistor value (Rsns) of 24mOhm and WEBENCH gives me a 10mOhm shunt. which one is correct?

2) If I calculate the values of the whole circuit using the application notes, the values are very different overall from the WEBENCH Design. Which one should I take in consideration?

3) If I want to change the current output of my design in WEBENCH I get a limit of 7A maximum, according to the tool I should be able to get 20A top. Why is this?

4) I tried to simulate the typical application note found in the datasheet that has a frequency of operation of 500khz, but the tool is limiting the frequency to 350khz. I wanted to make the same circuit in order to make comparisons of the applications to see if WEBENCH tool is giving me the close values to the ones calculated in the application note.

Thank you very much for your help!

Kind regards,

Joel

  • 0
    TI__Guru 59001 points
    Hi Joel
    1)Peak inductor current is ~13A at 42V input. 25mOhm x 13A =0.325V which is less than 500mV current limit threshold. It seems a lot of margin with 10mOhm.
    2) Which user guide are you referring to ? Pleas let us know the link. If there is a difference between the design example in the datasheet and WEBENCH result, please follow the example in the datasheet. The example in the datasheet is fully verified design on the bench.
    3) 20A output current is not realistic. Handling 20A input current is possible depending on thermal design.
    4) Frequency in the WEBENCH is limited to make the component temperature less than the its limit. LM5022-Q1 switching frequency is not limited to 350kHz, it can be programmed up to 2.2MHz.
    Regards,
    EL
  • 0 in reply to EricLee
    Prodigy 120 points
    Hello Eric,

    Thank you very much for your fast answer.

    The datasheet I'm using is this one: www.ti.com/.../lm5022.pdf from page 14 onward.

    I will follow the calculations using the applications notes then!

    Thanks again!

    Regards,

    Joel