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Ripple current selection of the inductor in the buck converter

Xiaoying Lu
Expert 3230 points
Other Parts Discussed in Thread: TPS62130A, TPS62180, TPS62184, TPS566238, TPS566231, TPS54620

When designing a buck converter, many application notes recommend that we are supposed to choose a suitable inductance to make the inductor ripple current as 20% to 40% of the Iout. Just want to make sure what the number comes from, is it derived by some mathematic calculations? What will happen if the inductance is larger or smaller? Thanks.

  • 0
    TI__Guru*** 142860 points

    Hi Xiaoying,

    I wrote this technical article a while ago, which should answer your question: 

    Let's look at a specific example.  What Vin, Vout, and Iout do you need a power supply for?

  • 0 in reply to Chris Glaser
    TI__Expert 3230 points

    Hi Chris,

    Thanks a lot for your great reply!

    I think you have given a great perspective on low-power step-down converters.

    Firstly I am looking at the traditional application, for example, 12V Vin, 3.3V Vout, 2-6A Iout, and the 20% to 40% ripple guarantees CCM condition and reasonable peak current limit.

    Actually I haven't thought about the low-power step-down converters before,  when I look at the datasheet of TPS6213A, I find that there is Table 5 to recommend the inductance. And you say that it requires selecting the inductance to match the compensation for stability. Can you help explain how we choose the inductor considering the stability? Thanks.

    Regards,

    Xiaoying

  • 0 in reply to Xiaoying Lu
    TI__Mastermind 21765 points

    Hi Xiaoying,

    Yes, you are right, stability is also a crucial criteria especially for internally compensated architectures like DCS and DCAP. TPS62130A uses DCS control architecture and needs a certain range of output inductor and output capacitor values to ensure stability.

    Is 6A the maximum current you are looking at? If so, the TPS62130A may not be an option as it can support upto 3A. However, there are many other options which you can check here: https://www.ti.com/power-management/non-isolated-dc-dc-switching-regulators/step-down-buck/buck-converter-integrated-switch/products.html#p238min=1.5;12&p238max=12;30&p451max=6;6&sort=p451max;desc    

    There are newer low cost devices like TPS566231/TPS566238. TPS566238 can allow you to stay in CCM for the entire range of operation by allowing negative inductor currents (check datasheet and Forced PWM operation). For fixed frequency peak current mode control, you can check TPS54620/22 which has external clock synchronization. There are other options like TPS62180/TPS62184 which are dual-phase devices that could be used for greater output voltage accuracy and higher efficiency but need an additional inductor. 

    I would recommend checking out the link above and also try to find out if there are any additional feature requirements for your design. Let us know if you have any more questions.

    Thanks,

    Amod