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TPS92518-Q1: N-channel or P-channel Power Stage

Part Number: TPS92518-Q1
Other Parts Discussed in Thread: LM3409, TPS92518

Hi Team,

Based upon the TPS92518-Q1 datasheet, it appears that the device is able to drive N-channel and P-channel FETS. Would it be possible to help me understand when it makes sense to use P-channel and when it makes sense to use N-channel FETs?

Thank you,

Jared

  • Hello Jared,

    The TPS92518 drives N-channel MOSFETs.  A part like the LM3409 drives a P-channel MOSFET.  They aren't interchangeable, on an N-channel MOSFET the gate is pull high with respect to the source, a P-channel MOSFET gate is pulled low with respect to the source.  Both the TPS92518 and the LM3409 are high side MOSFET buck converters.  The TPS92518 requires a boot capacitor to generate a voltage above Vin to drive the N-channel MOSFET.  The LM3409 does not need a boot capacitor since the gate is pulled below Vin to turn on the P-channel MOSFET.

    Best Regards,

  • Hi Irwin,

    If that is the case, why is the application diagram showing P-channel FETs?

    -Jared

  • Hi Jared,

    That must be a drawing mistake, note that the source is still at the bottom (which is how an N-channel is drawn) which would make the diode backward for a P-channel MOSFET.  I don't know where the creator of the block found that part.  It does need to be an N-channel, if you placed a P-channel in that position it the correct orientation the TPS92518 could not enhance the MOSFET since the gate drive only goes positive.

    Just an FYI.  If you had a choice between N-channel and P-channel MOSFETs, performance wise you  would chose N-channel.

    Best Regards,