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DRV2625: Implications for skipping calibration or hard coding calibration at assembly.

John Griffith
Mastermind 21576 points
Part Number: DRV2625

Hello,

My customer is trying to figure out how to handle the calibration routine for the DRV2625 for production and is looking for some feedback. 

  • Could they characterize a number of LRAs and program the average calibration information into their MCU at assembly to use for all production boards? Obviously there is part to part variation with the LRA, but do we think that individualized calibration is needed?
  • If you hard code the calibration at assembly, is there an issue with drift or changes in resonance or magnitude over time? Do we think it is okay to do calibration at t=0 and never change these values again? Alternative is running the calibration at every power up where you would capture any changes over lifetime, but this complicates the FW on the device and turn on time.  
  • They plan to only use haptics as a feedback for touch screen presses on their device, do we think that part to part variation or aging is enough for a user to notice any changes if the calibration values are not ideal?

Thanks in advance! 

John

  • 0
    TI__Genius 10290 points

    Hi John, 

    Thanks for reaching out.

    1. Per section 8.6.7 Calibration Routine in the data sheet, "Variation occurs between different actuators even if the actuators are of the same model. To ensure optimal results, TI recommends that the calibration routine be run at least once for each actuator". Along with once per actuator, it is recommended to check the performance as well. If the performance is satisfactory, the calibration routine can be run once per start up or store the results in memory and rewrite them to the device upon power up.  

    2. The auto resonance tracking feature is not dependent on calibration. When in closed loop mode, the device will actively track and drive at the resonance frequency. Referring to the previous answer, we recommend running it at least once per actuator, so it will not be necessary to run calibration at every power up. Instead, the calibration results can be stored in memory and rewritten to the device upon power up. 

    3. Calibration is for the back emf so the actuator can go slightly above the rated voltage during automatic overdrive and braking (but not exceeding the overdrive clamp voltage). As the LRA ages I don't believe the variation would be very noticeable by the user, but this would depend on the specific LRA and how drastically its performance degrades as it ages. 

    Regards,
    Sydney Northcutt