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DRV8825: Erratic behaviour of stepper motor

Part Number: DRV8825
Other Parts Discussed in Thread: DRV8847

Hi,

We are using stepper motor driver DRV8825 in our project. Schematic for the same is given below.

Stepper motor type we are using in our project is 4 lead bipolar type, operated in 1/2 stepping mode. We are facing an issue with one of our prototypes in which stepper motor direction of rotation is not getting controlled, but the number of the revolutions stepper motor rotates is as expected. Every time I switch ON or OFF power to the stepper motor, the direction of rotation of stepper motor is changing in a random fashion.
 We have probed DIR, STEP, FAULT, V3P3OUT pin of driver IC but no issues were observed. Please let us know what is causing the stepper motor to behave erratically. 

Thanks,

Indhu N

  • Hi Indhu,

    Can you elaborate on the data you took on the DIR pin? If my understanding is correct, you set the DIR pin to the same state (high or low), but the motor runs in different directions when you power cycle it. When the motor runs in different directions, the state of of the DIR pin remains unchanged?

    Are you disconnecting and reconnecting the motor to your setup? If so, is there a chance that you are switching any of the motor wires by mistake? This can change motor direction too, even though the DIR state is the same.
  • Hi James,

    Thanks for quick reply.

    DIR pin is kept high continuously. The motor is expected to run clockwise every time we switch OFF and ON the power supply to the stepper motor, the direction of rotation of stepper motor is changing in a random fashion.

    Answering your questions,

    Are you disconnecting and reconnecting the motor to your setup?
    No, the motor is not disconnected from the setup while it is running.

    If so, is there a chance that you are switching any of the motor wires by mistake?
    Checked the wire connections, no issues were found. Wires are not interchanged either.


    We have done some checks from our end and found that pin number 2 of the motor connector is having a loose connection. We tried to simulate this issue by taking one of our working setup with DRV8825 motor driver and cut pin 2 wire connection between motor driver and stepper motor. Every time I switch ON or OFF power to the stepper motor, the direction of rotation of stepper motor is changing in a random fashion.

    Another thing we observed is if the power supply to stepper motor is kept continuously ON it continues to rotate in one direction (clockwise or anticlockwise) when DIR pin is kept continuously HIGH and reverses direction if the DIR signal input is changed to LOW. Why is this behavior happening?

    Why is driver IC not stopping the motor when one of the motor phases is down? Why is there no indication from DRV8825 to the microcontroller using the nFAULT pin? Is there any way to determine if one of the motor phases is down?

    Thanks,
    Indhu N
  • Indhu,

    The DIR pin controls direction of the stepper motor. When you see that the direction of the motor when the state of DIR changes, this is correct operation.

    The DRV8825 does not have open-load detection, so it will not report that a motor phase is disconnected. The DRV8847 is our only stepper driver right now that has this feature. However, it will only detect open load during power-on, if nSLEEP is toggled, or you use the DRV8847S and write the OLDOD bit over I2C.