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LM74670-Q1: Reverse polarity using N MOSFET

Sudhir Gupta
Intellectual 285 points
Part Number: LM74670-Q1

I have a concern about the use of N-Ch MOSFET as the pass element with the diode controller.

As the source/substrate is now (according to datasheet and AN)  connected to V++, does that affect channel resistance. I wonder, if there are any comparisons made for operating characteristics, for both operating conditions - Source/substrate connected to V- and  in reverse Source/substrate connected to V+.

Data/graphs will be most helpful.

Regards,

Sudhir

  • 0
    TI__Genius 16305 points

    Hi Sudhir,

    If i understand your question correctly, when source is connected to V- side, device will not power up because body diode of N-Channel MOSFET is reverse biased and no power to the IC.

    Source needs to be connnected to positive side of the power path.

    Regards,
    Kari.

  • 0 in reply to Karikalan Selvaraj
    Intellectual 285 points

    Hi Kari,

     Thanks for the reply. I am sorry that I was not able to present the question in a better format.

     I do understand that under LM74670-Q1 controller the N-MOSFET will only turn when the source is connected to V+ supply . My question relates to the lowest Rds resistance of the selected N-MOSFET under LM74670-Q1 control vs. the lowest Rds resistance, when the  MOSFET is placed in a conventional manner (and without LM7470-Q1 control) with source connected to V- supply. I suspect that the selected N-MOSFET will display greater Rds resistance under LM74670-Q1 control and consequently resulting in greater thermal loss.

     

    Kind Regards,

    Sudhir

  • 0 in reply to Sudhir Gupta
    TI__Genius 16305 points

    Hello Sudhir,

    Can you please explain with a figure (hand drawn):

    1. selected MOSFET with LM74670-Q1 

    2. conventional MOSFET ?

    Regards,
    Kari.