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DRV8833: DRV8833 deadband

Kenji
Intellectual 530 points
Part Number: DRV8833

Hi.

I have a question about DRV8833 deadband.
I'm driving VCM using DRV8833 at carrier frequency of 90kHz.
VM (motor power supply voltage) is 4V.

And I confirmed that there is a dead band when the duty is in range of ±3%.
At 90kHz, duty 3% is equivalent to 333ns in time.

From From the specification, summing of Tr(rise time) and Tf (fall time) is 180ns+160ns=340ns.
Although it is different from the measurement conditions in the specification, this time is almost the same as the time width at duty 3%.

My question are,

#1. Dead band will occur at a duty that is less than the time width of sum of Tr and Tf?
#2. Is there a motor driver with a short time of Tr and Tf?
#3. Is there a way to compensate the dead band in software without changing the carrier frequency?

  • 0
    TI__Mastermind 37683 points

    Hi Kenji,

    1. To ensure that the device operates properly, the time for the rise (Tr) + falling time (Tf) needs to be greater than the specified dead time so that the appropriate FETs are enabled at the beginning of the next PWM cycle. 
    2. To better answer your question, are you planning on using the DRV8833 to drive a stepper motor or brushed DC motor? what is the operating voltage and current needs for your application?
    3. Let me research this and I will get back to you with an answer by the end of the day on 7/27 US time.
  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hi Kenji,

    I apologize for the late response.

    Unfortunately, there is no software solution to compensate for the dead band since that is hard coded into the device. You are going to have to decrease the PWM frequency or increase the duty cycle.

  • 0 in reply to Pablo Armet
    Intellectual 530 points

    Hi Pablo-san

    We want to drive VCM at 90 kHz of carrier frequency.
    Does TI have a motor drive that drive over 100 kHz?
    I think that it is possible to reduce the effect by selecting a motor driver that can drive at a higher frequency.

    The figure below shows the actual dead band measurement results at carrier frequency of 90kHz.
    In range of duty ±5%, deadband occur.

  • 0 in reply to Kenji
    TI__Mastermind 37683 points

    Hi Kenji,

    I am having a little bit of trouble understanding the plot you attached. I don't see a time domain axis. How are you making the dead time calculation?

    In regards to motor drivers with higher frequency capabilities. We do have motor drivers capable of greater than 100kHz PWM frequency. However, I'm not sure if that will help in your case. You are worried about the dead time being less than the Tr+Tf due to your small duty cycle. In your case you'll want a driver with faster Tr and Tf times to ensure the dead time is longer than Tr+Tf. Please let me know if I misinterpreted your comment.