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UCC24612: Need for resistance between VGS

Hirotsugu Kobayashi
Mastermind 9530 points
Part Number: UCC24612

Hi team,

A resistor is often placed between VGS of the secondary side synchronous rectifier IC, but there is no specific description in the data sheet.

Is there a function inside the IC to prevent gate voltage malfunction?

Best regards,

  • 0
    TI__Guru* 85616 points

    Hello,

    Your inquiry is being reviewed and I will get back to you shortly.

    Regards,

  • +1 in reply to Mike O'
    TI__Guru* 85616 points

    Hello,

    Generally a gate resistor is added to dampen ringing that could be caused from trace inductance and gate capacitance.

    Most designers generally put down between 2.2 and 5.1 ohms to reduce ringing.

    In the past the largest I have sized that resistor to allow for max current.

    R = or < Vgate/Idrive_max.

    To critically damp ringing you could use the following equation.  It sets Q to 1.

    L is the trace inductance and C is the FET gate capacitance. 

    R =  (L/C)^0.5

    Regards,

  • 0 in reply to Mike O'
    Mastermind 9530 points

    Hi Mike,

    Thanks for the answer, but my question is Gate-Source resistance.

    There are cases where it is used to prevent incorrect operation, but there is no mention of it in either TI's datasheet or EVM.

    Does this IC have a special function to prevent gate malfunction?
    If there is no function, is it okay to place a resistor between Gate and Source?

    Best regards,

  • 0 in reply to Hirotsugu Kobayashi
    TI__Genius 12795 points

    Kobayashi san,

    Please check the EVM design on ti.com

    https://www.ti.com/lit/ug/sluubv6/sluubv6.pdf

    You can put a resistor in between, like 10ohm.

    Best,

    Ning

  • +1 in reply to Hirotsugu Kobayashi
    TI__Guru* 85616 points

    Hello,

    My answer was for the gate resistance.

    If you have ringing at the gate of the FET it will create design misbehavior.

    The device does not have a special function to prevent operation.

    You can add a resistor gate to source if you want.  However, if you do I would recommend adding 1K or greater to not slow down the gate drive. 

    Years ago it was standard to add 10 k ohm from gate to source. 

    Regards,