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DRV2603: Missing pulses in drive waveform

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Replies: 22

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Part Number: DRV2603

Hello,

I have an LRA application that seems to be working fine (it buzzes), but when I inspect the waveforms they're not matching the DRV2603 datasheet Figure 2.  The driver seems to be skipping pulses and I was wondering if someone could comment if this is somehow expected behavior.  In the attached scope capture we're running a test sequence where we drive the haptic at 25, 50, 75, and 100%. 

Thanks,

Arthur

  • Hi, Arthur,

    Could you share scope capture with the PWM signal at full scale? Is it the first part of your graph above? It seems that this part coincides with the one in figure 2 of datasheet?

    In addition, what voltage level and frequency are you using at the PWM? And what is the voltage level at VDD?

    Best regards,
    Luis Fernando Rodríguez S.
  • In reply to Luis Fernando Rodriguez S.:

    Hi Luis,

    At full scale drive, the PWM signal pulses low once per cycle for about 200nsec.  The PWM frequency is 30.6kHz and the amplitude is about 3.3V.  

    I think the part I've circled in purple matches Figure 2 of the datasheet, but everything else seen here in the red differential drive waveform does not.

    Edit:  VDD voltage is 3.5V

  • In reply to Arthur Thompson27:

    Hi, Arthur,

    Do you get the same results without using a load?

    The datasheet mentions that the full-scale output voltage depends of the LRA ( www.ti.com/.../drv2603.pdf ).

    Best regards,
    Luis Fernando Rodríguez S.
  • In reply to Luis Fernando Rodriguez S.:

    Luis,

    Can you please explain if the missing pulses are part of the expected "braking" behavior or related to Back-EMF? I'm getting 6.8Vpp, 2.4Vrms which seems normal. But the actual waveform only hits 6.8Vpp for a fraction of the cycles, highlighted by me in purple. The rest of the time, the peak to peak waveform is smaller. Is this normal?

    Thanks,
    Arthur
  • In reply to Arthur Thompson27:

    Hi, Arthur,

    Could you tell me what do you get at the output when there's no load connected, please?

    As the datasheet mentions, the LRA architecture may affect the output voltage and consequently its waveform.

    Best regards,
    Luis Fernando Rodríguez S.
  • In reply to Luis Fernando Rodriguez S.:

    Luis,

    Here is the waveform at both outputs and the differential output with no load connected.  What are you able to determine from this information?

    Thanks,

    Arthur

  • In reply to Arthur Thompson27:

    Hi, Arthur,

    I'm thinking that probably the output waveform only behaves as the datasheet mentions under the recommended operating conditions. Have you tried to increase the VDD level to 5V and see if there are differences? Also, do you know if there's a change on VDD or EN pins when the you got a wrong waveform?

    Best regards,
    Luis Fernando Rodríguez S.
  • In reply to Luis Fernando Rodriguez S.:

    Hi, Arthur,

    Excuse me, do you have any update on this? Could you take a look at my suggestion above?

    Thank you.

    Best regards,
    Luis Fernando Rodríguez S.
  • In reply to Luis Fernando Rodriguez S.:

    Hi Luis,

    I don't see anything about 5V being recommended for VDD. I'm running VDD at 3.5V, which is about halfway in between the 2.5-5.2V recommended operating range given in Table 6.3.

    Thanks,
    Arthur
  • In reply to Arthur Thompson27:

    Hi, Arthur,

    I agree with you regarding the VDD range specified in table 6.3. However, all the measurements and the plots were taken with some test conditions. The test condition was VDD = 5V in this case. So, I was wondering if this value could make a difference on the results that you are getting.

    Best regards,
    Luis Fernando Rodríguez S.

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