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MCT8316Z: Direction of the motor changes only after reset via nSleep

Part Number: MCT8316Z

We're trying to use MCT8316ZT to control a BLDC motor, and so far we're able to bring it up to the point where the motor is spinning as expected at no load. However, changing the DIR pin is displaying the following behaviour:

  • When the motor is spinning in one direction, switching DIR pin from high -> low or vice versa has no effect
  • Once the nSleep pin is switched Off and back On only then the direction reverses
  • Tried applying the brake input after switching the DIR pin while the motor is running. The motor stops instantaneously, but even after removing the brake input the motor continues to spin in the same direction
  • Tried giving 100% and 30% duty cycle, no change in observation
  • Tried varying the Voltage on I_lim pin from 1.25 to 1.65V, same observation.

Any clues on what we may be missing here?

Regards

  • Hi Vikas, 

    Our team will aim to follow up shortly and provide a response by end of week at latest. 

    In the meantime, can you help share an image of your schematic so that we can help screen for issues?

    It may be possible that there's a wiring connection error or mis-label 

    Best Regards, 
    Andrew 

  • Hi Vikas,

    Are you working on MCT8316Z EVM or custom board? Can you make sure the nFault pin is pulled High (1.8V to 5.0V) before applying voltage on the VM pin?

    Regards,

    Vishnu

  • Hi Andrew, Vishnu

    Thanks for getting back. We got a PCB made as per the EVM gerber and soldered the relevant components on top of it for bringing up the prototype. I suspect it could be a soldering issue as the MCT was soldered without a proper stencil. We're rectifying that and I'll update here once there're new observations.

    One fundamental question though - If the motor is spinning a load in one direction at a certain RPM, what happens if you toggle the DIR pin on MCT8316Z? Will there be a braking torque applied by the motor limited by the current as per the ILIM setting? That is how it would happen in case of a brushed DC motor with current-control drive and it's fairly simple to imagine- as only one leg of the H bridge is active at a given time and so the direction of current (and therefore torque) is easily controlled.

  • Vikas,

    I'll get back to you shortly.

    Regards,

    Vishnu

  • Vikas,

    When the DIR command is changed, the device starts commutating in opposite direction which generates the braking torque and starts to spin in the opposite direction.

    Regards,

    Vishnu.

  • Hi Vikas,

    Do you need any more assistance with this thread? If not, please mark as "Resolved". 

    Thanks,
    Aaron