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LM7480-Q1: Cdv/dt series resistor

Takuma Ito
Expert 5200 points
Part Number: LM7480-Q1

hi, can you tell me how to determine the R4 value in below picture ?

I want to know how to set resistance, accuracy, dissipation of resistor 

  • 0
    TI__Guru 57737 points

    Hi Takuma,

    Thanks for reaching out to us. Let me get back to you by Monday. 

  • +1 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Takuma,

    The resistor serves two purposes:
    • When HGATE is intended to turn OFF: It blocks charge from the soft start capacitor to allow the HGATE pull down the MOSFET gate as fast as possible.
    • It prevents an excessive surge of charge from going into the GATE pin. 

    A 100 ohms resistor will serve the purpose.  

    Current flows through this resistor for short duration of time only when the Gate is being driven High or pulled Low. Considering the small amount of power loss in it for short duration of time, the power dissipation or accuracy is not important.