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LM5170EVM-BIDIR: Altering the EVM Design to 24V instead 12V

Martin Hopf
Prodigy 40 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170, LM5175

Dear TI

I purchased two of these EVM as a starting point for an automotive  Buck/Boost converter design, The EVM offers all features we need, so I want to use them as a reference design for basic operation principle validation.

I want to modify the existing design as we need 48V to 24V, not 48V to 12V. I assume as the design is "symmetric" that I will not need to touch any of the power semiconductors.

More, as I assume the limiting factor in the design is current not voltage I hope that I can still use 60 Amps on the 24V side and get twice the power "for free". My design target is a 24/48 bidirectional automotive buck/boost converter with about 4kW continuous power. Therefore I think about paralleling 2 or 3 EVM as a starting point.

Can you show me the right corners to tweak?

BR Martin 

  • 0
    TI__Mastermind 21720 points

    Hi Martin,

    Thanks for reaching out with your questions and using the LM5170.

    To change the output voltage the low feedback resistor of the buck leg just needs to be changed to set the output voltage to 24V. I also suggest taking a look at the LM5170 quick-start calculator. This will help to calculate any other component changes.

    Please let me know if you have any questions.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Prodigy 40 points

    Dear Garrett

    Thanks for your quick support and presenting the link to the design tool. I understood you just want me to start with changing R78/R76 ratio, right? To verify, I downloaded the tool. Not sure everything is correct - when I open the spreadsheet Excel complains about an external binary source not being present: "LM5175 Buck-Boost Quickstart Tool -- r9 (version1).xlsb".  I cannot find this file in the zipped Folder which I download..The Zip file only contains LM5170DESIGN-CALC.xlsx.

    Although despite this the sheet seems to work without the mentioned file, I am not sure everything is ok. E.g. when I increase the number of phases in the tool, the main inductor value also increases. I would have expected a decrease of the value… Can you briefly comment on this?

    Best Regards

    Martin

  • 0 in reply to Martin Hopf
    TI__Mastermind 21720 points

    Hi Martin,

    Thanks for downloading the quick-start calculator. I have never seen that error before but the calculator should work fine without the binary file it says it is missing.

    To change the output voltage you have the correct resistors. These just need to be changed to  move the output voltage up.

    If the number of phases increased the current conducted per phase decreases. Assuming that the same inductor current ripple ratio stays the same then the inductance value needs to increase to keep the ripple ratio the same. This is why the inductance value increases.

    Please let me know if you have any questions.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Prodigy 40 points

    Hi Garrett,

    thanks for commenting on this. I will start to evaluate the results of the tool next week. It seems to work although it complains.

    Thank you

    Martin