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LM5117: MOSFET selection of Webench Design

Cedrick
Expert 8270 points
Part Number: LM5117

Hi,

Good day.

Our customer has generated the design using webench. You can find it here: webench.ti.com/.../SDP.cgi. Their question is why the M1 and M2 are different transistors? What is the reason? Can they use same transistors here?

Looking forward to your input. Thank you.


Regards,

Cedrick

  • 0
    TI__Guru 73502 points

    Hi Cedrick,

    For a buck regulator design with a high step-down ratio (low duty cycle), it's common to choose a high Rdson, low capacitance FET for the high-side FET as the conduction losses are lower yet that FET sustains all the switching loss. In contrast, the low-side FET is conduction loss dominated, so low Rdson is thus more suitable.

    The same voltage rating can be used for both FETs - just ensure the rating is above the peak SW voltage overshoot. A rating of ~150% of Vin-max is typical.

    Regards,

    Tim