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DRV8304: Minimum PWM frequency useable for driving a low-speed 3-phase BLDC motor

Francois Arnaud
Prodigy 20 points
Part Number: DRV8304

Hello,

We would like to know the minimum PWM frequency useable for the DRV8304 38-V 3-Phase Smart Gate Driver, please.

The datasheet SLVSE39B –NOVEMBER 2017–REVISED JULY 2018, specifies a maximum of 200KHz and an example of 45KHz is given.

But there is no mention of the minimum useable range.

For example, for a low-speed BLDC 3-phase motor with a switching frequency of about 200Hz - is it possible to use the DRV8304?

I look forward to hearing from you soon.

Best regards.

  • 0
    TI__Genius 15635 points

    Hi Francois,

    There isn't a specific "minimum" PWM frequency listed in the datasheet, but operating at very low frequencies (such as below 1 kHz) might not be advisable due to potential issues with torque ripple and less efficient motor control. Operating in the more typical range (20 kHz and above) is generally best for reducing acoustic noise and improving overall motor performance.

    Regards,

    Yara

  • 0 in reply to Yara Al Shami
    Prodigy 20 points

    Hello Yara,

    Thank you for your prompt and helpful reply.

    However, I believe that I found the particular answer in the document TI TIDUE42–February 2018, Reference design with a DRV8304, page 14, copied below.

    There is a confusion between PWM period and PWM frequency which is not the usual definition Frequency= 1 / Period.

    "3.1.2.2.1 PWM_PERIOD
    The PWM_PERIOD parameter sets the value in capture and compare register 0 of Timer_B0. The
    Timer_B0 is initialized to operate at a 16-MHz clock. Use Equation 7 to calculate the PWM frequency.

    The TIMER_A0 PWM is configured in up-down mode.

    PWM Frequency (Hz) = 16 MHz / ((2 x PWM_PERIOD) - 1)

    For example, with PWM_PERIOD = 400, PWM frequency ≈ 20 kHz."

    I believe this answers to my question - we can use low-speed motors even if the PWM Frequency is above 20KHz.