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MC33063A-Q1: Reverse polarity protection using P-MOSFET

Tylor
Prodigy 170 points
Part Number: MC33063A-Q1

Hi,

We are protecting input power against reverse polarity using P-Channel MOSFET. We referred multiple documents and ended up with confusions on Drain/Source connection. In some places the voltage input is connected to Drain and Load is connected on Source but in other places it is viceversa. I would like to know which way is correct.

I took SNVA717 as example,

1. VIN connected to Drain of MOSFET

2. VIN connected to Source of MOSFET

Thanks in advance !

  • 0
    TI__Guru* 75895 points

    Hi Tylor,

    Thank you for posting.  The first diagram is for protection against battery reverse polarity.  In the 2nd diagram, the PFET is uses a an inrush current limiter, and the reserve polarity protection is fulfilled by DBLK.

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 170 points

    Hello Youhao,

    In Both circuit MOSFET is getting Input voltage but on different Pins Drain and Source based on use case. In 2nd Circuit the voltage is again applied to Source and load is connected on Drain. What is the best way to connect voltage input on which pin and Load on other pin?

    We designed a circuit to protect the system from reverse polarity and over voltage as well. Please check and let us know if any changes needed.

    D88 - Zener 36V Breakdown

    D89 - 18V VBr

    we also need your suggestion on LC filter calculation or the components values. DCIN will be 12-28V and the system will consume up to 10A.

    Thank you !

  • 0 in reply to Tylor
    TI__Guru* 75895 points

    Hi Tylor,

    Like mentioned previously, the FET on the left was for reverse polarity protection in which the drain of the PFET is connected to the battery.  The ET on the right is for inrush limit when you first file apply the battery.  Its source needs to be connected to the side facing the battery.  

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 170 points

    Hi Youhao,

    we have better understanding now on the FET connections but not on the LC filter that we will raise as another question in forum.

    Thank you ! :)

    Best Regards,

    Tylor