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DRV8305: Noise during acceleration and deceleration - cycle by cyle current regulation - 6 steps - 1PWM mode

Yan-Kilian Rey
Prodigy 40 points
Part Number: DRV8305


Hello,

I am using a DRV8305 in 1 PWM mode without any sensors (BEMF).
For the regulation, I am using the cycle by cycle current method with the SOx outputs.

My problem is : the motor makes a ringing sound when It is accelerating and mostly when it is decelerating.


Current Shunt Amplifiers Config :

    - Gain = 10V/V
    - k = 4
    - CS Blank = 500 ns
    - DC_CAL_CHx : normal operation
    - Current Shunt = 50mΩ

When I want to decelerate, I set the DAC1_OUT1 to 0 (0V).
However, SOx_Output cannot go under 0.825V, so the duty cycle of my PWM is equal to 0 during deceleration.

Also, during deceleration, the motor current is negative and Vbus is alterate (voltage overshoots around 5V depending of the setpoint).
Vbus = 24V when stable.

Here is the electronic schematic :

I removed C45, C46, C50, C51, C52, C53, R46, R52, R55, C34 and C55 on my board.
R57 and R257 are shorted.
R75 replaced by a current shunt of 50mΩ
A third capacity of 330uF is on the Vbus but not appearing on this schematic.

BEMF is stable and well centered.

Best regards,

  • 0
    TI__Mastermind 27646 points

    Hi Yan,

    Thank you for your question!

    Let me look over this in more detail and get back to you early next week.

    Regards,

    Anthony Lodi

  • 0
    TI__Mastermind 27646 points

    Hi Yan,

    You mentioned that the motor current is negative during deceleration and that the supply voltage is pumping up sometimes by 5V. This indicates that when you decelerate, since you are no longer applying a PWM (PWM is low), then the current in the motor is flowing through the body diodes of the high side FETs back into the supply which is pumping up the supply voltage. This will occur if the phases are in Hi-Z mode, which may be the case if the PWM input is left low. I would recommend decelerating more slowly if possible, instead of immediately bringing the PWM input to 0. I would recommend decreasing the duty cycle of the PWM over time to control the amount of current that flows back into the supply during deceleration.

    1xPWM mode has some limitations when compared to 3x PWM mode and 6x PWM mode, such as not having the option of braking the motor through turning on all the low side MOSFETs and allowing the current to dissipate through the low side MOSFETs. The method that you can achieve in 1xPWM mode is the coast method, where all the phases are in high-Z mode. You have to be careful with this method to ensure that the supply voltage doesn't get pumped up too much since the motor current flows back into the supply. 

    Regards,

    Anthony Lodi

  • 0
    Prodigy 40 points

    Hi Anthony,

    Thanks for your reply.

    I did some modifications since last time.

    Now the minimum value of the duty cycle of the PWM is 7% instead of 0 : it reduces the noise during the deceleration.
    To do that, I am not longer in cycle-by-cycle current regulation because I could not set the minimum duty cycle precisely.
    So I moved on a classic PWM command.
    I could also decrease the duty cycle progressively, but I need to decelerate the motor very quickly.

    Morever, as you mentioned in your reply, I need to dissipate the motor energy.

    I could use the 6xPWM mode, but I have a question : Can I use the dwell during deceleration to dissipate this energy?

    The dwell function is a feature of the 1xPWM mode, description in page 18-19 of the datasheet.
    For your information, I am using PWM Active Freewheeling.
    Regarding the datasheet, every low side MOSFETs are turned on when PWM is low while dwell is active.

    I tried to put a screencap of the datasheet, but for some reason I cannot add pictures on this message.

    Regards,

    Yan

  • 0 in reply to Yan-Kilian Rey
    TI__Mastermind 18981 points

    Hi Yan, 

    Our team is currently out of office today for July 4th holiday in the US - but we will review your question and aim to provide a response by end of the week. Thanks!

    Best Regards, 
    Andrew 

  • +1
    Prodigy 40 points

    Hi,

    I tried to activate the dwell function during deceleration and it is working perfectly.
    The motor is no longer generating ringing sound during deceleration. The noise has been totally removed.

    I did not try to come back to a cycle-by-cycle current regulation with a minimum PWM of 0%, but I guess it may work now.
    Be sure to have good transistors that can dissipate a lot of energy. Just in case, I will stay with a minimum duty cycle of 7%.

    Regards,

    Yan

  • 0 in reply to Yan-Kilian Rey
    TI__Mastermind 27646 points

    Hi Yan,

    Glad to hear that you were able to resolve your issue! 

    Regards,

    Anthony Lodi