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DRV8935PEVM: DRV8935 EVM GUI Configuration for Unipolar Stepper Motor.

Tom Tsao
Expert 1900 points
Part Number: DRV8935PEVM
Other Parts Discussed in Thread: DRV8935

Tool/software:

Dear TI team,

I’m using the DRV8935 EVM and have some questions regarding its compatibility and configuration when driving a unipolar stepper motor. 

  1. The motor is a unipolar stepper type. Is it suitable to drive it using the DRV8935 EVM? If needed, I can share the datasheet with you privately for confirmation.

  2. In the EVM GUI, the green circled section appears to be for setting PWM – is this correct?
    For the red boxed inputs IN1 to IN4, how should these be configured to drive the motor properly?

  3. I tried selecting “Step” in the green circled area. The motor coil center tap was not connected to any voltage, and the motor was able to operate after starting. This seems like the CPU is simulating a bipolar drive method. However, since the selected device is DRV89xx, which theoretically does not match this drive method, why is the motor still able to operate?

  4. The attached file mentions two unipolar driving methods: Low-Side Drivers and Half-Bridge Drivers.What are the main differences between these two methods?

sloa312.pdf

Thank you for your support!

  • +1
    TI__Mastermind 45445 points

    Hi Tom,

    Thank you for your post.

    Tom Tsao said:
    The motor is a unipolar stepper type. Is it suitable to drive it using the DRV8935 EVM? If needed, I can share the datasheet with you privately for confirmation

    The GUI and EVM firmware was configured for driving bipolar stepper motor not a unipolar type. I assume you have a 5-wire unipolar stepper motor. The 5-th wire common / center taps of both A & B coils can be left unconnected and the rest of the wires A, B and C, D can be connected to the EVM and driven in full-step mode.

    Tom Tsao said:
    In the EVM GUI, the green circled section appears to be for setting PWM – is this correct?
    For the red boxed inputs IN1 to IN4, how should these be configured to drive the motor properly?

    PWM is for driving brushed DC motors with each half-bridge and PWM control. For stepper motor the below must be selected.

    Tom Tsao said:
    I tried selecting “Step” in the green circled area. The motor coil center tap was not connected to any voltage, and the motor was able to operate after starting. This seems like the CPU is simulating a bipolar drive method. However, since the selected device is DRV89xx, which theoretically does not match this drive method, why is the motor still able to operate?

    This is because in full-step mode both windings are energized simultaneously, So the center taps will be at (almost) the same potential and there won't be any cross current flow (except for small current due to potential asymmetry of the windings). So in full-step mode unipolar 5-wire motor will work with a bipolar driver with the center tap left unconnected. While this is not perfect it is usable in most cases.

    Tom Tsao said:
    The attached file mentions two unipolar driving methods: Low-Side Drivers and Half-Bridge Drivers.What are the main differences between these two methods?

    Typical unipolar motor coils requires only a LS (low-side) driver. The common wire is typically connected to +ve power supply. The advantage is low cost because only LS FETs are required. Half-bridge drivers would be useful when current chopping is used for regulation to help with fast current decay particularly while microstepping. Controlling these also becomes more complex with all the decay modes compared to simple LS driver. Thank you.

    Regards, Murugavel