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DRV8805 Output issue

masahiko shimizu
Guru 11235 points
Other Parts Discussed in Thread: DRV8805

Hi

My customer is using DRV8805.
He has a issue.

STEP signal is not inputed, But DRV8805 output voltage to motor.
Please see attached file which is detail waveform.

This event isn't to add a capasitor of 0.1uF "between the 1-Pin (VM) and GND" and "between the 2-Pin (VCLAMP) and GND".

What is the cause of this issue?
Could you advice me?

Best regards
Shimizu

issue.xlsx

  • 0
    TI__Mastermind 21320 points

    Hi Shimizu,

    This event isn't to add a capasitor of 0.1uF "between the 1-Pin (VM) and GND" and "between the 2-Pin (VCLAMP) and GND".

    Can you clarify what this statement means?

    The DRV8805 is a low-side driver. The output waveform could be explained by a protection circuit of the DRV8805 enabling and the DRV8805 outputs being disabled (output pulls up to VM through motor winding. Can you examine the nFAULT pin during this condition?

  • 0 in reply to Nicholas Oborny
    Guru 11235 points

    Hi Nick

     When the issue happen, there is no capacitors near the VM pin and VCLAMP pin(with respect to GND).  

     But this issue doesn't happen if the 0.1uF capacitor is added  near VM pin and VCLAMP pin(with respect to GND).

     Does an incorrect operation happen because of being no capacitors near VM pin and VCLAMP pin?

     If it is correct, How many / much capacitor is needed? Is it same as EVM?

     Customer sets fault pin opened.

     but I got waveform fault pin which is opened at no capacitors near VM and VCLAMP.

     Please see attached file.

    Thanks

    Shimizu

    issue2.xlsx

  • 0 in reply to masahiko shimizu
    Guru 11235 points
    Hi Nick

    How is the progress?
    If you advice about the following information, I can close this issue.
    -Does an incorrect operation happen because there is not decoupling capacitors near VM pin and VCLAMP pin?
    -> Is there a possibility of this event?
    -How many / much capacitors is needed? Is it same as EVM?

    The comment of decoupling capacitor or Bulk capacitor is not showed in datasheet.　

    Thanks
    Shimzu
  • 0 in reply to masahiko shimizu
    TI__Mastermind 21320 points

    Shimzu,

    The waveform shows that nFAULT is always LOW. They will need to add an external pull up resistor to monitor the device fault status (pin is open drain).

    I recommend following the same bypass capacitor placement that is utilized on the EVM (0.1uF + 0.1uF). Bulk capacitance is determined by the application requirements.

  • 0 in reply to Nicholas Oborny
    Guru 11235 points
    Hi Nick

    Thank you for your support.
    I informed that capacitor(decoupling and bulk) should be placed like EVM to customer.
    and I asked customer to send waveform me. It is what added capacitor(decoupling and bulk) to VM and Pulled up nFault.

    Already, this issue was improved to add capacitor(decoupling and bulk) near VM by customer.

    Thanks
    Shimizu