• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 1 answer
  • Subscribers 29 subscribers
  • Views 609 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DRV8323R: PWM Control Modes Pros and Cons

Mark Guastaferro
Genius 11645 points
Part Number: DRV8323R


The DRVC8323R can support 1xPWM, 3xPWM and 6xPWM modes.  What are the pros and cons of the different PWM methods?  Is there an App Note or White Paper that describes the use cases for the different PWM control options?

  • 0
    TI__Mastermind 24401 points

    Hey Mark,

    I will aim to provide a response by Thursday.

    Best Regards,

    Akshay

  • 0
    TI__Mastermind 24401 points

    Hey Mark,

     

    Thank you for your patience.

     

    As Andrew mentioned in the email, the number of PWMs needed depends on the system considerations along with how much control is needed.

    • “From system resource overhead perspective, more PWMs means more GPIO’s are needed from the MCU to generate these PWMs, and more PWM signals means more switching losses
    • For level of control, things such as dead-time insertion would be benefit of having more PWMs”

     

     

    I would like to mention a few more details about each PWM mode to better highlight some differences.

     

    In 6x mode you are able to get each half bridge to provide a low, high or a high impedance (Hi-Z) state. In case both the INHx and INLx are on at the same time then the DRV outputs a high Z state to prevent shoot-through.

     

    In 3x mode, you now control the half-bridges themselves. The INLx pin will determine if the half-bridge is in high-Z or not. So, you lose some degree of individual FET control.

     

    In 1x mode, the drv uses an internal state table to commutate the motor. There is one PWM signal and the other inputs will be logic level signal from external MCU or from a hall sensor to determine which state the motor is in.

     

    Finally, the independent mode allows for the most control. The input pins directly match the high side and low side driver. In this mode it is possible to turn on both the high side and low side FET at the same time causing a shoot through condition.

     

    For more information I would recommend reading section 8.3.1.1 of the following datasheet.

    https://www.ti.com/lit/ds/symlink/drv8323r.pdf

     

    Hope this offers some clarification.

     

    Best Regards,

    Akshay

  • 0 in reply to Akshay Rajeev Menon
    TI__Genius 11645 points

    Hi Akshay,

    Thanks for the information, it is helpful but I think I need more information from a motor control point of view (BLDC motor in this case). Why would one want to use more PWM control signals? 

    The dead-time control example makes sense, but are there other reasons to consider? 

    For example, if an application required accurate speed control, are more PWM signals beneficial compared to 1xPWM control? 

  • 0 in reply to Mark Guastaferro
    TI__Mastermind 24401 points

    Hey Mark,

    I will consult with the team and aim to provide response early next week.

    Best Regards,

    Akshay

  • 0 in reply to Mark Guastaferro
    TI__Mastermind 24401 points

    Hey Mark,

     

    Having more PWMs isn’t going to affect the accuracy of the speed control. More PWM signals let you control individual FET rather than having the device automatically control two FETs at the same time. PWMs have more to do with gate driver operation.

     

    As far as the accuracy and the speed of MOSFET switching, it is controlled by the IDRIVE.

    Delays in switching are due to the added deadtime and any propagation delay.

     

    Hope this offers some clarification.

     

    Best Regards,

    Akshay

  • 0 in reply to Mark Guastaferro
    TI__Mastermind 18981 points

    Hi Mark, 

    Closing thread for now due to inactivity - can you let us know if the problem has been resolved? 

    Please let us know if further support is needed on this question. Thanks 

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    TI__Mastermind 24401 points

    Hey Mark,

    Do you need any more support on this? Please let us know if the issue is resolved.

    Best Regards,

    Akshay

  • 0 in reply to Akshay Rajeev Menon
    TI__Genius 11645 points

    Hi Akshay,

    The information you provided helped settle the issue.  Thanks for your help.