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DRV11873: Help for motor rotation problems

Rain Wang
Expert 1400 points
Part Number: DRV11873

Hi TI 

When using DRV11873 to start the brushless motor, the following three situations are encountered (we need the motor to rotate counterclockwise):

① Extreme situation: it rotates clockwise all the time;

② Common situations: clockwise rotation at intervals (clockwise rotation - stop - clockwise - stop...);

[The maximum instantaneous clockwise rotation speed shall not exceed 150rpm]

③ Occasional situation: stop and rotate counterclockwise (turn and stop, the speed is extremely low, visible to the naked eye)

Preliminary analysis of starting process: once the equipment obtains PWM signal, it will start the motor with 100% duty cycle until sufficient BEMF is generated (4 zero crossings are required); Once this happens, the device will enter the closed-loop control and enter the command speed according to the PWM input.

Question:

1. Why does the motor chip always rotate clockwise after acquiring PWM signal? What might be the cause? How do we debug through hardware or software?

2. Once the PWM signal is obtained, can the motor be started without 100% duty cycle and with low duty cycle? What parameters need to be adjusted?

Please analyze the above, thank you

The circuit schematic diagram is as follows:

  • 0
    TI__Mastermind 18916 points

    Hi Rain, 

    Thanks for posting your question to the e2e forum - 

    I've assigned this thread to a team member and we'll aim to provide a response by middle of next week. 

    Also, is this the same e2e thread as a separate post below?

    https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1160944/drv11873-the-drv11873-startup-is-abnormal

    Best Regards, 
    Andrew 

  • 0
    Genius 5040 points

    Hi Rain,

     In your circuit, the CS pin is configured to have 2A max limit, but the chip has 1.5A max and so you should correct this.

    1. As far as motor rotation issue, have you tried to change the direction by pull up pin FR and see if the initial rotation changes to CCW instead of CW? (If the motor UVW were mixed up with the chip UVW then it could cause the rotation in reverse.)

    2. During starting to rotate, then chip always drive the motor 2 phases with 100% pwm duty cycle to guarantee it can rotate the motor (this is like pulling the rotor magnet N pole with a moving S pole on the stator, without knowing the two vector fields should be at 90 degrees, and so it is running at very low efficiency until the BEMF is detected then the driver can drive the motor at higher efficiency as it now knows where are the rotor magnet poles). So it has to drive the motor at 100% to ensure the motor is rotating, and you cannot change the duty cycle lower, which I don't know why it is the issue for you. Maybe you have a low resistance motor and not a fan with high resistance wirings? Can you measure the resistance between phase U and V of the motor?

    Can you post the datasheet for the motor?

    Brian

  • 0
    Genius 5040 points

    On this "Common situations: clockwise rotation at intervals (clockwise rotation - stop - clockwise - stop...);"

    I think it stopped due to over current protection, then re-started again. So check if the phase current is too high causing thermal protection by the chip by divide the supply voltage by the motor phase resistance and see if it is higher than 1.5A

    Brian

  • 0 in reply to Brian Dang
    TI__Mastermind 18916 points

    Hi Brian,

    Appreciated on the recommendations!

    Best Regards, 
    Andrew 

  • 0 in reply to Andrew Liu
    TI__Mastermind 24405 points

    Hi Rain,

    I agree with Brian's recommendations. Please check and let us know your feedback.

    Regards,

    Vishnu

  • 0
    TI__Mastermind 18916 points

    Hi Rain, 

    Closing this thread - please let us know if you need further assistance, and help mark the answer above as 'resolved' if it answered your question. Thanks!

    Best Regards, 
    Andrew