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TPS62867: Inductor Value

Daniels Kurgs
Prodigy 180 points
Part Number: TPS62867

Hello Team,

all related designs to the TPS62867 converter mention typical inductor values of 220nH, but we would like to increase this value to 1uH to limit the inductor ripple for smaller loads.

The datasheet mentions that any other LC filter configurations need to be tested or simulated - is there anything in particular we need to pay attention to when simulating this design in PSPICE for TI?

I imagine this is important because we cannot adjust the internal compensation.

Thanks,

Daniels

  • 0
    TI__Genius 14876 points

    Hello Daniels,

    Are you only willing to reduce the output ripple ? If so, you can also use the FPWM mode by pulling VSET/MODE to high at startup.

    As you may have seen in the datasheet, I would not recommend the use of a 1uH inductor. By increasing the inductor value, you will reduce the current slope and this may disrupt internal circuitry measuring the current variation and end up having troubles recognizing output/current variations.

    You can have a look at the PSPICE for TI and focus on what the SW node would look like. Though, I would suggest to evaluate your design on the TPS62867EVM.

    Let me know if you have further questions.

    Thanks a lot!

    Regards,
    Dorian

  • 0 in reply to Dorian Brillet de Cande
    Prodigy 180 points

    Hi Dorian,

    thanks for the quick response!

    I was planning on using the FPWM mode anyway, yes. The intended use would be to power an FPGAs I/O banks, so minimizing ripple and the converters output impedance is important for us.

    My only source of confusion here is the often mentioned rule of thumb for buck converters: try to keep inductor ripple to less than 30-50%.

    In our case, with a 1.2A load, the output ripple would go well over 80%. If we decide to go with the small inductor and have high ripple, I imagine we just need to make sure that the inductor does not saturate or overheat and that the output capacitors can deal with the ripple.

    Is there anything specific to this part that we should know about?

    Thanks again,

    Daniels

  • +1 in reply to Daniels Kurgs
    TI__Genius 14876 points

    Hello Daniels,

    I recommend you to have a look at the folowing:

    https://www.electronicdesign.com/power-management/article/21801119/does-inductor-ripplecurrent-percentage-still-matter-in-lowpower-stepdown-converters

    TPS62867 was designed and tested to have best performances with a 220nH inductor. With an highly integrated solution like TPS62867, selecting a 220nH inductor will ensure best control-loop stability and achieve optimal operation.

    Let me know if you have more questions or comments here.

    Thanks a lot!

    Regards,
    Dorian