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DRV8434S: starts without step command

Jim Teunis
Intellectual 290 points
Part Number: DRV8434S

As soon as I set the EN_OUT bit to 1 the motor starts spinning, even though the STEP line is held low. If I do give a pulse on the STEP line, the motor starts behaving very erratically, changing direction all the time and vibrating. Setting the EN_OUT bit is the only thing we do, no other data is transferred.

What could be the issue?

  • 0
    TI__Mastermind 37683 points

    Hi Jim,

    Can you provide your full register configurations.

  • 0 in reply to Pablo Armet
    Intellectual 290 points

    Hi Pablo, thanks for your reply. We make two SPI transactions to the device.

    First we write 0b00001010 0b00001010

    As we understand it, this will write 0b00001010 to CTRL5, this will set the microstep mode to 1/256.

    Next, we write b00001000 0b100011110

    In our understanding, this writes 0b10001111 to CTRL2. This is supposed to set EN_OUT high while keeping TOFF and DECAY to their defaults.

  • 0 in reply to Jim Teunis
    Intellectual 290 points

    On further inspection, it seems we had swapped two motor connections during trouble shooting. So output A was connected to one side of winding A and one side of winding B. For output B vice versa. Possibly the driver was trying to hold the motor, but failing because of the missed connection?

    Now, with the correct connection, we have the opposite problem. The motor does not start. I do see some pulses on all the output pins. They seem quite narrow to me. The motor is a known good motor, we have also tried other brand new motors.

  • 0 in reply to Jim Teunis
    TI__Mastermind 37683 points

    Hi Jim,

    Thank you for the information. Please allow my some time to review. I will be OOO tomorrow and be back on Monday. I will provide a reply on Monday.

    Thanks in advance for your patience.

  • 0 in reply to Pablo Armet
    Intellectual 290 points

    Hi Pablo, we found the problem. The issue was that we had not disconnected VREF on our PCB. This of course caused the motor not to turn. We then swapped the motor wires because we thought that could be the reason that the motor was not spinning. This combination of problems made the stepper motor run without step command and behave erratically when it was given a step command. The issue is resolved for now.