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DRV8434A: learning mode question

Peter Xu
Expert 6050 points
Part Number: DRV8434A
Other Parts Discussed in Thread: DRV8434S

Hi team,

My customer has several questions when using DRV8434A.

1. One of the parameters used in calculating full-scale current is TRQ_DAC. I didn't find a definition in the datasheet, can you show me the definition?

2. In the working mode and stall detection mode marked in green below, is it necessary to perform a learning mode whenever the chip is reset? Can the stall threshold data be saved when the device powered-off?

3. The stall threshold mode (circled in yellow) mentions apply threshold to TRQ_CNT/STL_TH pin. The threshold voltage that needs to be applied the TRQ_CNT/STL pin is a threshold below the red box, and has nothing to do with the output threshold from the learning mode in the green box. Am I right?

4. As the blue line is crossed, it seems that only the rightmost working mode does not need to actively stall the motor. So is it possible to determine the threshold for the yellow circle at the design stage? Or does this threshold have to be calibrated for each motor during production?

Regards,

Peter

  • 0
    TI__Mastermind 19380 points

    Hi Peter,

    1. TRQ_DAC is used to scale the full-scale current (IFS) of a stepper motor. Typically, the VREF voltage is set to a constant 3.3 V, then the IFS can still be scaled over SPI by setting the TRQ_DAC bits in CTRL1 register. 

    2. Unfortunately, the device can't save the learned data after reset. The STL_LRN bit in register CTRL5 is '0' by default and must be set to '1' to enable automatic stall learning process. This bit automatically returns to '0' when the stall learning process is complete and therefore, the learning process will have to be repeated after reset.

    3. Yes, you are correct. The torque count is taken from the learning mode and then a desired stall threshold voltage is applied to the TRQ_CNT/STL_TH pin. The STL_MODE = DVDD only enables the stall detection mode. 

    4. Stall Threshold Mode must be selected while the motor is spinning in Torque Count Mode.

    Best,

    David

  • 0 in reply to David Medis
    TI__Expert 6050 points

    Hi David,

    David Medis said:
    1. TRQ_DAC is used to scale the full-scale current (IFS) of a stepper motor. Typically, the VREF voltage is set to a constant 3.3 V, then the IFS can still be scaled over SPI by setting the TRQ_DAC bits in CTRL1 register. 

    DRV8434A is controlled by GPIO and it cannot be controlled by SPI, and it does not contain any register inside. I read the DRV8434S datasheet, its default value for TRQ_DAC is 100%. Should we use 100% fixed in DRV8434A's equation?

    Regards,

    Peter

  • 0 in reply to Peter Xu
    TI__Mastermind 19380 points

    Hi Peter,

    Yes, you are correct. The DRV8434A cannot be controlled by SPI, my apologies. 

    In calculating the full-scale current you would not include the TRQ_DAC scalar.

    The equation would be as follows:

    Best,

    David