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LM5146-Q1-EVM12V: LM5146-Q1-EVM12V low side/ high side fets

Matthew Odinotski
Prodigy 120 points
Part Number: LM5146-Q1-EVM12V

Hello,

It's not clear to me why Q1 and Q2 are 2 different N-Fets, both on the Evaluation board, and when using Webbench.  On the Evaluation board, the high side fet is NVMFS6B25NL, and the low side fet is NVMFS6B14NL. Can we simply use the NVMFS6B14NL for both the high and low sides? (lowest Rds, and higher current)

thanks

Matthew

  • 0
    TI__Mastermind 49587 points
    Hi Matthew,

    It depends on the duty cycle. For low duty cycle applications (large step-down voltage conversion), the low-side FET conducts for a large portion of the switching period and thus has high conduction losses. Then a low Rdon FET makes sense.

    Conversely, the high-side FET determine switching performance and switching losses to a large extent, so choosing a low capacitance and higher Rdson device is preferred.

    So, by appropriate selection of FETs in a buck regulator application, the respective losses in each device are optimized.

    Regards,
    Tim