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P or N Mosfet for the buck converter

GARAM AN
Intellectual 1960 points

Hello,

I want to know the difference between using P and N mosfet for the buck converter.

I know that Rdson for the P mosfet is high, but it does not need to make floating driver circuit.

Rdson for the N mosfet is low, but it needs to make floating driver circuit, so using N mosfet is little bit complicated for the circuit.

what is the floating driver circuit for the N fet?

What is the different using P and N mosfet?

Thank you

  • 0
    TI__Genius 15135 points

    Hi, GARAM

    In the generic CMOS process, for same Rdson, the area of P mosfet is about 3 times area of N mosfet, which is caused by difference mobility of electron and hole.

    Although using N mosfet for high-side mosfet will be a little bit complicated, but it is still worth doing it.

    So using N mosfet is mainly to reduce the die size which will reduce the IC's cost.

    Below is simplified floating driver diagram for your reference.

    When switching node LX is low, LDO output V7V will charge Cb, the Cb provides the power for driving high-side N mosfet.  

    If using P mosfet, it doesn't need Cb.

    Besides, there must still have detailed differences in other control circuit, we don't need to care about it, the final purpose is to achieve output voltage conversion.