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LM74700-Q1: full conduction mode

Dongbao Zhou
Expert 4170 points
Part Number: LM74700-Q1


Hi,

According to the mosfet selection part, LM74700 is recommended to operate in regulated conduction mode, may i know the reasons behind? And if the part works well in full conduction mode (forward voltage higher than 50mV, let's say 200mV) in nominal current ?

Thanks

Dongbao

  • 0
    TI__Genius 16305 points

    Hi Dongbao,

    It is recommended to operate the MOSFET in regulation mode for nominal current range and park the maximum (worst case) load current towards 100mv or 200mV forward drop.

    This helps in better reverse turn off time as the MOSFET Vgs is much closer to Vth, than in full conduction.

    Vgs during regulation is around 4V to 6V for a 3V Vth MOSFET. To turn off the MOSFET, now Vgs has to drop from 4V to under 3V and the margin is only 1V and this is much faster turn off than a full conduction where Vgs is 12V and the Vgs has to drop to <3V, margin of 9V and this means larger reverse turn off time. 

    Regards,
    Kari.

  • 0 in reply to Karikalan Selvaraj
    TI__Expert 4170 points

    Hi Kari,

    Thanks for your comments.

    In my customer's application, they don't have very strict turn off time limitation (<1ms). That's to say, apart from the turn off time concern, LM74700 works in this application?

    Dongbao

  • 0 in reply to Dongbao Zhou
    TI__Genius 16305 points

    Hi Dongbao,

    Yes, if reverse turn off time is not a big concern, then you can operate the MOSFET beyond regulation --> in full conduction all the time.         

    Regards,
    Kari.

  • 0 in reply to Karikalan Selvaraj
    TI__Genius 16305 points

    Hello Dongbao,

    If you think, I have answered your question, click "this resolved my issue" button.

    Otherwise let me know if you have further comments.

    Regards,

    Kari.