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CSD17483F4: Capacitance vs Frequency Characteristics

Harish kumar
Intellectual 435 points
Part Number: CSD17483F4

Hi,

  Input capacitance (Ciss), Output capacitance (Coss) and Reverse transfer capacitance (Crss) are defined on a particular frequency (i.e. 1 MHz). So what is the significance of this frequency and how does it affects my MOSFET selection?
And also, how these parameters vary with frequency?

Regards,

Harish Kumar

  • 0
    TI__Expert 7405 points
    Harish,

    Thanks for the question.
    Frequency of 1MHz is a practical selection based on the available instrumentation for measurement (e.g. standard capacitance bridge). The 1MHz value is a commonly used frequency for specifying capacitance on discrete part datasheets across the power device industry.
    The capacitance will not vary very much within a factor of 10 of 1MHz, eg 100kHz to 10MHz.
  • 0 in reply to Chris Bull
    Intellectual 435 points
    Thanks Chris.
    I want to calculate the efficiency and these capacitance parameters contribute to switching losses.
    I'm driving the gate at 500k and 2MHz frequency, so how much my switching losses will vary with these frequencies?
    -Harish Kumar
  • 0 in reply to Harish kumar
    TI__Expert 7405 points
    Harish,

    Yes you are correct that varying frequency will impact your switching losses linearly.
    Normally though is is charge and not capacitances that are used in the power loss equations our team uses.
    For instance in th eapplication note here there is a detailed explanation of how to calculate power loss in a buck converter, www.ti.com/.../litabsmultiplefilelist.tsp , rather than you going through these calculations we also have an online tool that you could use here: www.ti.com/.../fetpwrcalc , if buck converter is the powerloss you are looking to estimate.
    We have calibrate this calculation method and found it to be really quite accurate.