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DRV8343-Q1: PWM duty resolution when using 10k PWM frequency

Takashi Onawa
Genius 13200 points
Part Number: DRV8343-Q1

Hi Team,

My customer wants to know how much duty resolution can DRV8343 handle.

According to datasheet, its max fpwm is 200k though, does this mean PWM frequency or frequency limit that DRV8343 can follow?

As a study case, when using at PWM frequency as 10KHz,
What is the minimum resolution that can be achieved?
What is the minimum pulse width that DRV8343 can handle?

Regards,

Takashi Onawa

  • 0
    TI__Guru 61380 points

    Onawa-San,

    I have assigned your post to the applications expert and he will get back to you tomorrow.

    Regards,

    -Adam

  • 0
    TI__Intellectual 2585 points

    Hi Onawa-san,

    The DRV8343S has a minimum 500ns dead time between switching the high side and the low side - this is what drives the 200kHz PWM frequency limit.

    I am still looking into the minimum resolution of the output signal timing, and will get back to you on this tomorrow.

    Thanks,

    Garrett

  • 0 in reply to Garrett Walker
    TI__Intellectual 2585 points

    Hi Onawa-san,

    I missed a digit when calculating the maximum frequency based off of the dead time. The 200kHz limitation has more to do with the maximum charge pump load - since each PWM cycle will charge and discharge the MOSFET, the charge pump load can be estimated as PWM Frequency * MOSFET Qg * Number of MOSFETS (usually 6). In the DRV8343, this load cannot exceed 25mA. 

    The inputs are synchronized based off of the internal oscillator, so minimum resolution that the DRV8343 can support will be 35ns. The minimum resolution of a 10kHz PWM signal will depend on the number of bits in the PWM counter, and the frequency of the clock in the customer's MCU.

    However, the minimum output pulse will depend much more than just this - IDRIVE strength, MOSFET switching speed, and dead time will all impact the minimum pulse width as well.

    Thanks,

    Garrett

  • 0 in reply to Garrett Walker
    TI__Genius 13200 points

    Hi Garrett-san,

    Thanks, I almost understood.

    One quick question.

    Where is the internal oscillator spec described in the datasheet?

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    TI__Intellectual 2585 points

    Hi Onawa-san,

    There is no spec for the oscillator speed in the datasheet, but it runs at a frequency of 28.5MHz. The input signals are synchronized on both the rising and falling edge of the clock - this leads to the 35ns resolution.

    Thanks,

    Garrett

  • 0 in reply to Garrett Walker
    TI__Genius 13200 points

    Hi Gattett-san,

    Thanks, I understood.

    Regards,

    Takashi Onawa