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DRV2605L: Issues with using multiple drivers at the same time while driving LRA's

Gregory York
Prodigy 10 points
Part Number: DRV2605L
Other Parts Discussed in Thread: DRV2605,

I am driving 4 DRV2605 chips to trigger LRA's on a single unit for haptic feedback from the same I2C message using the Buzz waveform. The issue I am seeing is that the even though each chip is receiving the 'Go' message at the same time they appear to be starting the actual waveform at different times this is leading to the 4 different LRA motors being driven in and out of phase with each other giving a very inconsistent haptic response to the user. Is there something specific that needs to be done to synch multiple drivers, or is this amount of drift normal from part to part?

I2C message to drv2605 OUT+

Out+ phase difference over the 4 drivers

  • +1
    TI__Mastermind 20715 points

    Hi Gregory, 

    I see you are using Closed loop mode to drive the LRA. in this case the DRV2605L is  tracking the resonant frequency of the LRA. It is likely the case that there is some variation between the 4 actuators (+/- a few Hz in resonant frequency) which is causing them to go in and out of phase.

    In closed loop mode there isn't a way to guarantee the LRAs will be synchronized. the LRA is basically a slave to the physical resonance frequency of the LRA/mounting system.

    You could however use Open loop mode to drive the LRAs. this mode will drive the actuator at a fixed frequency and assuming the polarity of the LRAs is the same they should begin in phase. ( i assume there will be some drift in frequency so for a long haptic effect they may still go out of phase)

    Regards,
    Arthur 

  • 0 in reply to Arthur Brown
    Prodigy 10 points

    Arthur, 

    Thanks for your response, changing the wave to an open loop mode to drive the LRA's did get them to start in synch. I am still seeing the drivers drift from each other over time even with no LRA present. Is there any way to correct for this drift or is this to be expected. The scope capture below is the OUT+ of 2 drv2605's triggered at the same time running the Buzz wave run at a 300ms durration.

    Regards, 

    Greg

  • +1 in reply to Gregory York
    TI__Mastermind 20715 points

    Hi Greg,

    So there is not much we can do to make the 4 drivers synchronize, there isn't a way to let them talk to one another to synchronize.

    I'm not sure how far along you are in your design, but have you considered using a single driver and driving all the LRAs in parralel?

    something like the DRV2510? the minimum impedance is 1.5 ohms, so its very likely capable to drive 4 of your LRAs in parallel. there wouldn't be any auto resonance tracking, but you could ensure they stay in phase

    Regards,

    Arthur

  • 0 in reply to Arthur Brown
    Prodigy 10 points

    Hello Arthur, 

    Driving the LRA's in parallel was able to provide the performance and level of synchronization that I was looking for, thank you. 

    regards,

    Greg