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DRV2624: Questions for resolutions of Auto Calibration

Byung-Min Yu
Prodigy 10 points
Part Number: DRV2624
Other Parts Discussed in Thread: DRV2604

Tool/software:

I would like to know the resolution and range of Auto-Calibration applied to DRV2624.


1. I understand that the calibration time is determined by Auto_cal_time [1: 0] and the center of calibration frequency is determined by the drive_time [4: 0].
    But I want to know the scan range according to each time of Auto_cal_time[1:0] (250ms, 500ms, 1S).

2. The Auto-Calibaraion of DRV2624 use detected B-EMF. 
    I wonder if the B-EMP value is processed as analog or digital signals. If it is digitally processed, I would like to know the processed B-EMP range and B-EMP value of LSB.

Thanks,

Byung-Min Yu

  • +1
    TI__Genius 10512 points

    Hi,

    I think you accidentally double posted, so I deleted the other post.

    Here are some answers:

    1. The drive_time is an initial guess on the resonance frequency. However, that is not the purpose of calibration. Auto-calibration and auto-resonance are two algorithms that run simultaneously in closed-loop mode. Auto-calibration is used to measure the back-EMF and set a reference target for future waveform playback. Auto-resonance runs independently.
      1. Longer auto-cal times are available for actuator that may take longer to settle, but generally the default time works for all motors.
    2. I assume you're talking about the back-EMF voltage for the entire part of this question. The signal is ultimately processed in the digital domain. There is an analog gain (BEMF_GAIN) and digital gain (A_CAL_BEMF) calculated based on the calibration result (the measure BEMF) for the programmed rated voltage setting. 
      1. The calculation for BEMF magnitude is not explicitly defined for DRV2624, but you can roughly use the equation in the DRV2604 datasheet - see "7.6.14 Auto-Calibration Back-EMF Result (Address: 0x19)" section. 
  • 0 in reply to Kelly Griffin
    Prodigy 10 points

    Thank you for your answer. In your answer, please tell me how auto-calibration and auto-resonance are different.
    So far, I knew that Auto-Calibration adjusts the resonance frequency.

    And I really want to know the frequency or B-EMF range of auto-calibration.
    ex) auto calibration range is 30hz and f0 is 200hz. Then, Auto calibration range is 170~230hz and motor having 160-hz f0 is not auto-calibration.

  • 0 in reply to Byung-Min Yu
    Prodigy 10 points

    And I really want to know the frequency or B-EMF range of auto-calibration. --> It means the auto-calibration or auto-resonance systems which maintains resonance frequency.

  • +1 in reply to Byung-Min Yu
    TI__Genius 10512 points

    Let me try to explain in a different way.

    Auto-calibration: This algorithm measures the BEMF level and sets a target BEMF level based on the programmed rated voltage. In closed-loop mode, the device will adjust the output drive voltage to make the BEMF level match this calibrated level. If the LRA is damped (by pressing on the LRA), then the driver will try to increase the BEMF level by increasing the output voltage. In closed-loop, the driver will adjust the output voltage to achieve the targeted BEMF voltage level (found in auto-calibration). 

    Auto-resonance: Resonance tracking algorithm is still being performed in closed-loop at every half-cycle of the output signal. It does not have any dependance on auto-calibration. This algorithm is adjusting the duration of the half-cycle output to align with the resonance frequency.

    You can check the LRA resonance frequency using register 0x05-0x06 during operation - please read the register description. 

  • 0 in reply to Byung-Min Yu
    TI__Genius 10512 points

    Use the equation I mentioned here and you can find the rough limits of the BEMF range.

    Kelly Griffin said:
    The calculation for BEMF magnitude is not explicitly defined for DRV2624, but you can roughly use the equation in the DRV2604 datasheet - see "7.6.14 Auto-Calibration Back-EMF Result (Address: 0x19)" section.