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LM74670-Q1: Vgs is abnormal

Betty Guo
Expert 7300 points
Part Number: LM74670-Q1

Hi,

customer use LM74760-Q1 as full bridge rectifier, the charge pump capacitor is 1uF/16V, use CSD18563Q5 as transistor.

but they found that there are noise on Vin and Vgs signal is abnormal. please see the below pictures.

could you help on this? thank you.

Vin:

Vgs:

  • 0
    TI__Genius 16305 points
    Hi Betty,

    I am looking into your question and will get back on this next week.
    Please let us know if you need an urgent response.


    Regards,
    kari.
  • 0 in reply to Karikalan Selvaraj
    TI__Genius 16305 points
    Hi Betty,

    For LM74670-Q1 to act as part in the full bridge rectifier, it needs to block any reverse current flowing back across the MOSFET it controls.
    In order to control this reverse current, LM74670-Q1 turns off the MOSFET by pulling gate down.

    In the waveforms, gate is being pulled down (Vgs = 0V) for every cycle. Because this pulldown current is fast, there is a bit of inductive ringing coupled onto VIN that you see when Gate is turned Off.

    I dont see a concern here. is the rectifier not functioning properly?


    Regards,
    Kari.