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DRV8881: Output Reverse Current

Shuji Ishiwata
Mastermind 7855 points
Part Number: DRV8881

Tool/software:

Hi All,


I have a question about the DRV8881.

Sometimes, a motor connected to the RV8881 may rotate due to external factors even when the power is not applied.
When this happens, a back EMF is generated from the motor.

How much reverse current can the DRV8881 tolerate?


Best Regards,
Ishiwata

  • +1
    TI__Mastermind 45445 points

    Hi Ishiwata-san,

    Thank you for your post in this forum.

    Shuji Ishiwata said:
    Sometimes, a motor connected to the RV8881 may rotate due to external factors even when the power is not applied.
    When this happens, a back EMF is generated from the motor.

    Yes this is correct. The BEMF generated will be a sine wave and will get rectified by the body diodes of the output FETs. This rectified DC voltage will be presented across VM and GND. The VM bulk capacitor will smooth the DC voltage.

    Shuji Ishiwata said:
    How much reverse current can the DRV8881 tolerate?

    Is the stepper expected to be rotated externally with VM unpowered at a steady speed? If so the VM must not exceed the VM operating voltage specifications. Because the driver is not powered it is likely the driver would likely be not enabled. Assuming this is true, except for the current flow into VM no other current flow is expected. The body diodes can support IFS level currents. Would the VM power other devices on the VM bus as well? If not this would be a non-issue except for voltage present on VM during the back motion. Because of rectification either direction will result with same DC level between VM and GND. I hope this helps. Thank you.

    Regards, Murugavel  

  • 0 in reply to Murugavel4637
    Mastermind 7855 points

    Hi Murugavel-san,


    Thank you for your reply.

    Thanks for your great support.


    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    Mastermind 7855 points

    Hi Murugavel-san,

    I have one additional question.
    You commented that you can support IFS (full-scale current), but is it correct to understand that you can support a value of up to 2.0A?

    Best Regards,
    Ishiwata

  • +1 in reply to Shuji Ishiwata
    TI__Expert 5340 points

    Hi Ishiwata-san,

    The DRV8881 can be powered with a supply voltage between 6.5 and 45 V, and is capable of providing an output current up to 2.5 A peak or 1.4 A rms per H-bridge.

    Best regards, 
    Mojtaba

  • 0 in reply to Mojtaba Afshar
    Mastermind 7855 points

    Hi Mojtaba-san,

    The prerequisite for my question is the IFS of the diodes when VM is not supplied.
    Can I understand that even in this case, a maximum of 2.5 A peak or 1.4 A rms per H-bridge is acceptable?

    Best Regards,
    Ishiwata

  • 0 in reply to Shuji Ishiwata
    TI__Expert 5340 points

    Hi Ishiwata-San, 

    Yes, the MOSFET and Body diodes are designed to work with current up to 2.5 A peak or 1.4 A rms per H-bridge.

    Best regards, 

    Mojtaba.