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Webench the diode requirement spec of boost converter

K. Sasaki14
Guru 10200 points
Other Parts Discussed in Thread: TPS55340

I would like to ask about the following URL WEBENCH design.

http://webench.ti.com/webench5/power/webench5.cgi?VinMin=3.2&VinMax=3.4&O1V=7.5&O1I=1.5&base_pn=TPS55340&AppType=None&op_TA=75&lang_chosen=ja_JP&optfactor=3

In this design, Webench requires the diode of lower bound Iout limit 4.125A. Why is this min value required? The diode average current is nearly equal to Iout 1.5A, and the peak current is nearly equal to inductor peak current. I think diode Iout spec of Webench is average current characteristic, thus I think 4.125A requirement is over spec for 1.5A output current.　I would like to know how does Webench decide this lower bound limit?

Best Regards,

Kohei Sasaki

  • 0
    TI__Intellectual 1370 points

    Hello Sasaki-san,

    http://www.ti.com/lit/ds/symlink/tps55340.pdf

    For TPS55340, as per datasheet selection criterion for Schottky Diode D1, Diode's average and peak current rating needs to exceed the average output curent(Iout/(1-D)) and peak inductor current. And so, we use the below equation to estimate the Io Minimim limit to be 0.8* Io_Tgt = 4.125A for your spec.

    Io_tgt in WEBENCH is calculated as  -

                         Io_Tgt = ((Iout/(1 - .DMin))* (1 +Ipp/2))/ D1_Io_Drt;

    Where we assume a derating factor D1_Io_Drt to be 0.75.

    Ipp = 0.2; and

    DMin = (Vout_Usr) - VinMin_Usr) / Vout_Usr);

    Hope this clarfies. Please let me know if you still have any concerns.

    Regards,

    Pavani Jella

    WEBENCH Design Center