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DRV2604L: Understanding Open Loop

Nicholas Carley
Genius 9945 points
Part Number: DRV2604L
Other Parts Discussed in Thread: DRV2604, DRV2625,

Hello,

I can't seem to find too much information in the datasheet about running drv2604 in open-loop. Can you verify my understanding?

  1. In open-loop, the waveform sent to the LRA is PWM with a frequency determined by the DRIVE_TIME register. If my understanding is correct, it seems like there is an issue with the drv2604
    1. The frequency of vibration is different from the specified DRIVE_TIME value with our LRAs.
    2. Changes to DRIVE_TIME doesn't seem to affect the acceleration waveform.

With the drv2625 EVM, I was able to compare the PWM waveform played out to the LRA and the acceleration waveform and verify that the programmed frequency (via OL_LRA_PERIOD register)  match.

There is no equivalent register as the OL_LRA_PERIOD for drv2604. Are you aware of any known issues with the open loop mode in the drv2604? Or do you know the proper way to program the drv2604 for open-loop operation at a specified frequency?

Thanks,

Nick

  • 0
    TI__Guru* 84915 points

    Hi, Nico,

    The main difference between the closed-loop and open-loop modes is the calibration of the device for the actuator to use. When the open-loop mode is selected, the overdrive and break parameters must be configured manually. In this mode, the auto-calibration cannot be made. However, close-loop mode has a back-EMF feedback that allows the internal algorithm to get the overdrive and break parameters. Consequently, the auto-calibration can be achieved.

    In order to program the open-loop parameters, it is necessary to apply some calculations based on the actuator characteristics. I strongly recommend to take a look at the information below. It is a .xls file that help to configure the DRV2604 for both close and open loop modes.

    slor114a.zip

    Please let me know if you have additional questions or comments.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Prodigy 90 points

    Can you tell me exactly which parameters need to be set for proper open-loop operation with the drv2604? My understanding is OD_CLAMP(register 0x17) for the max voltage and DRIVE_TIME(register 0x1B) for the frequency of the PWM waveform input into the LRA. Is that correct? Or do I need to worry about some other parameters? How do overdrive and auto-braking work in the open-loop mode?

    Thanks

  • 0 in reply to Abhipray Sahoo
    Prodigy 90 points
    I just discovered that the DRV2604L has a register OL_LRA_PERIOD at address 0x20. Setting the value here does change the PWM frequency.

    Thank you for your help!
  • 0 in reply to Abhipray Sahoo
    TI__Guru* 84915 points
    Hi, Abhipray,

    There are some differences between the DRV2604 and the DRV2604L. The register OL_LRA_PERIOD that you mentioned is particularly for the DRV2604L. The LRA frequency can be then modified with this register.

    By other hand, the DRV2604 requires of an external PWM input to determine the output drive signal. The user should drive the PWM frequency at 128 times the desired operating frequency.

    Best regards,
    Luis Fernando Rodríguez S.