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Power FET's ON resistance in Buck converters

Arpan Gupta57
Prodigy 40 points

Hello TI support team,

I observed in few buck converters parts that high side FET ON resistance is higher than the low side one (observed in few datasheets of TI parts).
As per my understanding, high side NFET suffers from substrate bias effect, but low side does not. Hence, high side FET on resistance appears higher than low side.

Could you please confirm if my understanding is correct? If not, could you please share the reason behind it?

Thanks & Regards,

Arpan Gupta

  • 0
    TI__Guru**** 191445 points
    Arpan,

    That is one possible reason. Many converters use P channel FETs for both low and high side switches. Many wide input voltage range converters use a lower resistance FET for the low side as typical duty cycles are low and the low side FET is on for a much longer portion of the switching cycle than the high side FET. Die size area is directly proportional to the FET RDSon. For these low duty cycle applications it is more efficient use of the same die size area to have a low RDSon low side FET and a higher RDS on high side FET than to have to same size FETs with a mid range RDSon. I hope this helps to clarify your question.
  • 0 in reply to JohnTucker
    Prodigy 40 points
    Hi John,

    Thanks for the clarification.

    Regards,
    Arpan Gupta