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DRV103: Duty Cycle Resistor Calculation at Other Frequencies

PY (Pengyu) Song
Expert 5860 points
Part Number: DRV103
Other Parts Discussed in Thread: DRV104,

Hi team,

For both DRV103 and DRV104, how to calculate the correct resistor value to set duty cycle for frequencies other than 5kHz, 25kHz and 100kHz listed in datasheet? For example, 500Hz. Is there any equation? 

  • +1
    TI__Genius 13300 points

    Hello,

    The formula to calculate the Rfreq is below:

    Iref = 1.3V/Rfreq

    so for 500 Hz (also in the table) Rfreq = 11.3 MΩ

    Vpwm = 2.75*Iref*Rduty

    By using the following table we can get the linear equation for D% to Vpwm:

    If we ignore below 10% and above 90% and choose a D% between 10 and 90 we will have more accurate results:

    D% (between 0.1 & 0.9) = 0.3903*Vpwm-0.4904

    So lets say at 40% duty cycle with Rfreq(500Hz) = 11.3 MΩ you want to know what Rduty to choose:

    Vpwm = 0.4/(0.3903) + 0.4904/(0.3903) = 2.28V

    2.28 = 2.75*(1.3/(11.3*10^6))*Rduty

    Rduty = 2.28/(2.75*(1.3/(11.3*10^6))) = 7.2 MΩ

    Let me know if you have any additional questions or need clarification.

    Regards,

    Kalin Burnside