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DRV2625: Automatic Braking when using RTP Mode

Mia Depta
Prodigy 10 points
Part Number: DRV2625

Hello,

for our research application we are using the DRV2526 haptic driver only in RTP/Open-Loop mode for amplitude and frequency control and only with I2C communications. We have found out that the LRA motors are being braked even with the brake disabled in the register. Here's a list of things that we tried to disable breaking:

  • In Register 0x23 Bit 6-4 set to 7 to disable breaking
  • In Register 0x08 Bit 6 set to 1 for open loop, Bit 4 set to 0 for no automatic breaking

We implemented the driver in this way: During startup calibrate and set the registers. When being used write the values of the amplitude and frequency into their registers and then start the motor with the GO Bit. To stop the motor we send it into standby.
We also tried to set the amplitude to 0 instead of standby but this didn't help either. When we want to stop, we expected to observe the motor coasting down. Instead it appears on the oscilloscope that it is being braked.

Have we overlooked something here for the DRV or is this perhaps a hardware related issue?

  • 0
    TI__Mastermind 27300 points

    Hi Mia,

    Apologies for the delay, our haptics expert is currently out of office and will comment as soon as possible.

    Regards,

  • 0
    TI__Mastermind 20755 points

    Hi Mia, 

    I think the issue could be bit 3 of register 0x08 will need to be set to 0 to disable automatic braking when entering standby .

    Are you observing the braking through an accelerometer or are you observing the DRV output pins?

    Regards,
    Arthur

  • 0 in reply to Arthur Brown
    Prodigy 10 points

    Hi, sorry for the late reply.

    We already tried setting the bit 3 of register 0x08, this sadly didn't help either.
    We are observing the braking behavior through the DRV output pins and by physical touch.

    To get a bit more into detail about what we're trying to achieve: We want to cycle through multiple LRAs to make it seem like they're all on at once, similar to how you'd multiplex LEDs. This setup has worked in the past with ERM motors and we're doing this because our application is limited by power consumption and battery size.

  • 0 in reply to Mia Depta
    TI__Mastermind 27300 points

    Hi,

    Our TI experts are out of office today for US holiday, please be patient as responses are delayed.

  • 0 in reply to Daveon Douglas
    TI__Genius 10512 points

    Hi Mia, braking in open-loop can be done 2 ways. One way is the AUTO_BRK_INTO_STBY register. The second way is setting a value to OD clamp less than mid-scale (8.6.8.2 in datasheet). The second option here reverses the phase of drive. Could you look closely at the waveform during braking and capture the OUT+/- pins?  From this image, we will be able to tell if the device is braking via method 1 or 2.