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LM5050-1: Question on Reverse Current

Mitchell
Expert 4915 points
Part Number: LM5050-1

Hi Team,

On the LM5050, we noticed there are two mechanisms dealing with reverse current.

If the reverse Vsd threshold (-28mV) is reached, a fast turn off circuit is activated to turn off mosfet quickly. In other cases, the gate controller actively regulates Vsd to be 22mv forward.

What's the behavior due to the 2nd mechanism (regulate Vsd to be 22mV) if we have a slightly reverse current. For example, if reverse current results in Vsd = -10mv, will gate voltage keeps decreasing and eventually fully shut the mosfet down? I'm guessing it will be a slow process compared with fast turn off feature.

Thanks,
Mitchell

  • 0
    TI__Genius 16305 points

    Hello Mitchell,

    Yes that is absolutely correct.

    Linear Regulation Scheme of LM5050-1:

    • IN-OUT > 22mV, increase VGS gate voltage, reduce RDS (ON) of MOSFET
    • IN-OUT < 22mV, reduce VGS gate voltage, increase RDS (ON) of MOSFET
    • IN-OUT > 100mV, fully enhance the MOSFET with VGS gate voltage >10V
    • IN-OUT <-28mV, turn off MOSFET by pulling GATE to SOURCE quickly VGS = 0V.

    For fast changing reverse condition, for example, when Input supply is shorted to GND, IN-OUT will exceed -28mV and MOSFET will be turned off to prevent reverse current.

    But when the input supply is disconnected, while the MOSFET is ON, current would start to reduce and the gate voltage is reduced continuously slowly, increasing the RsON of MOSFET. Eventually even a small reverse current would turn off the MOSFET.

    Regards,

    Kari.