• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 587 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.

DRV8308: Stationary Stationary Braking

Oscar Perez
Prodigy 45 points
Part Number: DRV8308
Other Parts Discussed in Thread: MCF8316A

Hello, 

We're developing a mobility device for our customer and we have locked the DRV8308 IC as the motor driver for the design. It will be used to drive a brushless motor. It is critical for safety that the motor can be put in a stationary mode where an external torque will not cause the motor to rotate. The braking function of the DRV8308 will turn on all the low-side FETs causing a braking force but this force is proportional to motor speed and is not adequate for stationary braking. The motor is still able to slowly turn when the motor driver is braking. 

We have observed in other devices a means to lock the rotor into a stationary angle. This is accomplished by pulsing the 50% duty cycle voltage waveform at 26KHz to all 3 motor phases at once. The slight time delay between the 3 phases voltages rising will allow some current to flow from phase to phase at the rising and falling edges.

Is there a mechanism to use the DRV8308 to drive all high-side and low-side FETs at once or take manual control of the FETs from a microcontroller?

This would be highly useful for us as we have already procured a large number of the IC and we require the braking to work as a stationary brake.

Thank you 

Oscar

  • 0
    TI__Mastermind 26046 points

    Hi Oscar, 

    You should be able to use the BRAKE pin from an external MCU to brake or coast the motor. BRKMOD = 1 allows all low-side FETs to turn on at once and work as a stationary brake. 

    Thanks,
    Aaron


  • 0 in reply to Aaron Barrera
    Prodigy 45 points

    Thank you for your reply but as I wrote in my first paragraph: "The braking function of the DRV8308 will turn on all the low-side FETs causing a braking force but this force is proportional to motor speed and is not adequate for stationary braking. The motor is still able to slowly turn when the motor driver is braking. "

    This has been tested and has shows it does not produce braking force when stationary and allows the motor to creep forward. 

    OP 

  • 0 in reply to Oscar Perez
    TI__Mastermind 26046 points

    Hi Oscar,

    I am reaching within my team for more information, let me get a reply back to you tomorrow. Thanks for your patience.

    Regards,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Mastermind 26046 points

    Hi Oscar, 

    More information from team:

    "Turning ON all Low side FET is called passive braking. The braking torque generated due to passive braking depends on Rds,on, so a smaller Rds,on for the MOSFETs can increase breaking torque.

    The controller can also use active braking by injecting DC current on any two motor phases. Braking torque can be controlled by adjusting the magnitude of DC current."

    I am not an expert on the DRV8308, is it possible to implement active braking with the controller? Or if not, can you decrease the Rds,on of the FETs as a possible option?

    Also as an FYI, is the customer set on DRV8308? If peak current is <8A and motor voltage is <35V maximum, then we recommend next-gen device MCF8316A (currently available for sampling). 

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    TI__Mastermind 26046 points

    Hi Oscar,

    Do you need more assistance on this thread?

    Thanks,
    Aaron

  • 0 in reply to Aaron Barrera
    Prodigy 45 points

    Thank you again for your interest.

    My client and other engineers insist there is  away to create a strong braking force by actively driving the motor backwards (against the direction of rotation)..

    I'm experimenting with that but I'm losing hope.

    Do you have any thoughts on this?

    --

    "Also as an FYI, is the customer set on DRV8308? If peak current is <8A and motor voltage is <35V maximum, then we recommend next-gen device MCF8316A (currently available for sampling). "

    That is a very interesting driver.. Unfortunately we are using much more than 8A in out application

    Thanks

    OP. 

  • +1 in reply to Oscar Perez
    TI__Mastermind 24415 points

    Hi Oscar,

    DRV8308 is a fixed function device so it is not possible to add any custom algorithm to the device. You are right that strong braking can be achieved by generating a torque in reverse direction. MCF8316A has several braking options but it can only support up to 8A peak current.  

    Regards,

    Vishnu