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DRV8889-Q1: The system risk from OL detect disabling

Kazuki Kuramochi
Genius 10495 points
Part Number: DRV8889-Q1

Hello expert,

Our customer is considering to disable open load detection(EN_OL=0) due to they cannot distinguish open load event happened or just electrical angle became 0/90/180/270deg.
Then, we want to know about the risk of disabling open load detection from the view point of system.

As far as my understanding for open load detection, it is just notify open load even and it don't have impact of device's behavior as like as other fault functions.
So I think there isn't the risk from disabling open load detection from the view point of IC level.
On the other hands, I cannot distinguish whether there is system level risk from disabling OL detection due to I don't know actual reason of why this device has OL detection.

Then, would you tell about why there is OL detection and whether there is risk of disabling OL detection from the view point of system?

Thank you and best regards,
Kazuki Kuramochi

  • 0
    TI__Mastermind 44595 points

    Hi Kuramochi-san,

    Thanks for reaching out to us via this forum. When the motor is spinning OL does not do a false report at 0/90/180/270deg. An OL will be reported only when the motor is stopped at these positions because one of the phases will be zero at these electrical angles. A potential workaround would be to disable OL before stopping the motor and enable OL after starting the motor. By this approach an OL condition can be caught at the system level. Another approach would be to track the electrical angle in the ECU/MCU and avoid stopping the stepper motor at those specific electrical angles. In this case OL detection can remain enabled both when motor is in hold and run mode.

    You are correct the OL detection is used only for identifying an OL condition and will not impact driver behavior. So, no risk from disabling OL from a driver IC functionality standpoint. 

    Additionally for low full-scale current settings IFS and with specific microsteps setting combination an OL condition may not be identified. This information is not in the datasheet as it may not affect most applications. What is the targeted IFS and microstep setting customer is considering for this application? If we can find out this information I can tell you whether it will be impacted by this limitation or not.

    I hope this addresses your questions.

    Regards, Murugavel

  • 0 in reply to Murugavel4637
    TI__Genius 10495 points

    HI Murugavel-san,

    Thank you for kindly explanation.
    Their concern for OL detection is when motor is stopped as you explained.
    So I understand that they need to disable OL detection but there isn't risk from the view point of IC behavior.

    By the way, is there any problem from open load event for the DRV8889-Q1's behavior?

    Thank you and best regards,
    Kazuki Kuramochi

  • +1 in reply to Kazuki Kuramochi
    TI__Mastermind 44595 points

    Hi Kuramochi-san,

    Yes, correct. According to the Fault Condition Summary table in the datasheet the device will be in normal operating condition regardless of OL fault, meaning the outputs will still be actively driving the required stepper phases.

    Regards, Murugavel