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DRV8884: External Components for Controlling RREF with a PWM Resource

Kazuki Kitajima
Intellectual 1480 points
Part Number: DRV8884

Hello team!

I would like to know there's any limitation for external components for controlling RREF with PWM resource.

Especially, C1 value in the picture below.

From my understanding, those values are flexible unless not affect PWM signal(larger cap value might attenuate inputting the signal?)

Please tell me the reference to choosing the external components.

Thank you for your support.

Best Regards,

Kazuki Kitajima

  • 0
    TI__Guru 56650 points

    Kitajima-san:

    1. First calculate maximum current of on Rref. According to Equation 2, the Vc1 is about if the full scale current is 1A and Rref is 15kohm.

    Vrref-Vdac= IFS* Rref/30k = 0.5V. Rref current is about 0.5V/15kohm=0.033mA.

    2. Make the maximum Rref current is much smaller than R1 and R2 current. Please check the MCU GPIO pin output current capability. If GPIO is 1mA at 3.3V. R1+R2=3.3kohm. Vc1= Vrref-0.5V=0.732. You can get R1 and R2 value.

    3. Make (R1//R2) and C1 filter time constant is much longer (may pick 10 times longer) than DRV8884 PWM switching frequency.