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LM74700-Q1: LM74700 as a Load Switch: can it drive back-to-back NFETs?

Ed Mellinger
Prodigy 70 points
Part Number: LM74700-Q1

Hello, I'd like to use LM74700 as a power path controller in an underwater robotic vehicle, due to it's low Iq and small size.  I would need to drive back-to-back NFETs (Source terminals connected) to achieve full bi-directional control.  Any issues with using LM74700 in this mode, e.g. changes to the gate drive circuit, etc?

thanks!

Ed M

  • 0
    TI__Genius 16305 points
    Hello Ed Mellinger,

    LM74700 does not support back to back NFET drive due to its gate drive topology. It turns off the MOSFET by connecting source to gate and hot-swap MOSFET will not turn off completely.

    Just to understand your applicaiton, could you please let us know why common source topology is required? Common drain does not help?

    Regards,
    Kari.
  • 0 in reply to Karikalan Selvaraj
    Prodigy 70 points

    Thanks, Kari.  Connecting the two NFETs in series, with source connected to source, allows the downstream one to serve as the ideal diode, and the upstream one to serve as the load switch.  I don't believe there's a way to do it if the drains are connected... in that case the two sources would be facing "outward" and the FETs would see very different gate-source voltages.

    Upon further study I see why neither connection will work with the LM74700, but I'm glad I asked.  Please let your marketing folks know there's a need for a charge-pump NFET controller like this, that only needs 60 uA... but with Load Switch capability!

    thanks,

    Ed