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DRV8889-Q1: Blockage detection

Part Number: DRV8889-Q1

Tool/software:

Our company has newly evaluated the customer's HUD project and requested that the bipolar stepper motor drive have the ability to detect locked rotor. After reviewing the drv8889-q1 specification, it can be understood that locked rotor detection can be achieved through phase difference or BEMF induced phase current waveform change time difference, which is not affected by motor current, coil impedance, ambient temperature, and supply voltage. Therefore, I would like to ask for your advice
1. Is it feasible for the high impedance 215 ohm coil internal resistance small bipolar stepper motor we use to be driven with a low current limit of around 40mA and a full step speed of approximately 400pps at low speed?
2. Can we prevent the BEMF reverse electromotive force caused by the mechanical structure's short-term obstruction (detected by a trigger switch in reverse) and the stopping process when the motor rotates to the limit position without judgment? For example, by setting the detection time limit for blockage and rotation to handle it.
3. Please also help evaluate the ability of drv8889-q1 stepper motor driver to detect and compensate for step loss. I understand that it can only monitor the input PWM step signal at most, but compensating or physically compensating for step loss in the final motor mechanical structure should be difficult to achieve from the driver IC end.

  • Hello Zhang,

    Thank you for posting in this forum and thank you considering the TI DRV8889-Q1 stepper driver. 

    1. Is it feasible for the high impedance 215 ohm coil internal resistance small bipolar stepper motor we use to be driven with a low current limit of around 40mA and a full step speed of approximately 400pps at low speed?

    We have found that with such low current micro size stepper motors the back EMF BEMF is very low and has poor SNR to allow stall detection in the DRV8889-Q1 to work reliably. You should experiment with 1/8 or 1/16 microsteps setting to see if you get reliable torque counts when the motor is running with no load and the torque count decreasing reasonably low to near 0 with a block or stall. You can connect the stepper motor to one of our DRV8889-Q1EVM and evaluate the stall detection function using the EVM GUI app. We have seen approx. 20 Ω stepper motors are available in similar sizes that work better for stall detection. 

    2. Can we prevent the BEMF reverse electromotive force caused by the mechanical structure's short-term obstruction (detected by a trigger switch in reverse) and the stopping process when the motor rotates to the limit position without judgment? For example, by setting the detection time limit for blockage and rotation to handle it.

    Using time limit approach should work without relying on BEMF based stall detection. I have seen this approach implemented in some end applications successfully. This works well for low torque output low current motors because there will be no mechanical damage even if the motor continues to be driven for some period of time while blocked.

    3. Please also help evaluate the ability of drv8889-q1 stepper motor driver to detect and compensate for step loss. I understand that it can only monitor the input PWM step signal at most, but compensating or physically compensating for step loss in the final motor mechanical structure should be difficult to achieve from the driver IC end.

    Because steps lost would be an arbitrary number of steps this cannot be detected by the DRV8889-Q1 and reported back to the driving MCU for compensation. 

    Regards, Murugavel