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DRV10983 problem at low speed / low current

Martin Oppermann
Prodigy 70 points
Other Parts Discussed in Thread: DRV10983

Hi,

I have an application, where the motor has to turn at low speed sometimes.

In this special case we are talking of speeds of around 1000RPM. Voltage is around 12V, current for motor about 10mA, Motor has 4 poles.

On some of my PCBs (abt. 10-20% of the 1st pre series production), the motor will suddenly stop at the low speed (around 1000RPM, 4 pole motor).

If I exchange motor with the components from a working device, the problem is still there, so I am sure, the problem comes from the driver chip.

Also the not-running motor works on another driver PCB.

In another posting in this forum I have read, that the DRV10983 is analyzing coil current to determine commutation time. So the question is, if there is some kind of minimum current? Or are there any other things to do to optimize motor operation under low speed/low current conditions?

Thanks for any hint,

best regards,

Martin

  • 0
    TI__Mastermind 26065 points

    Hi Martin

    Our experts will be noticed and get back to you later.

    Best regrads,

  • 0 in reply to Wilson Zuo
    TI__Expert 3010 points

    Hi Martin

    That’s correct; there is built-in back observer in DRV10983 which estimates back emf waveform based on phase current and motor parameters. Motor is commuted based on zero crossing of back emf signals.

    10.2.1 Design Requirements section in datasheet states that minimum operating current required is 0.1 A. So in your case, it seems current is low for observer to estimates back emf signals accurately.

    Can you provide information on fault triggering motor to stop? You can check details about fault in GUI on display tab or by reading status of register ‘FaultCode’

    Regards

    Krushal

  • 0 in reply to Krushal
    Prodigy 70 points

    Hi Krushal,

    thanks for your answer.

    I checked the FaultCode register and what I get is always the "abnormal Kt" error.


    Are there any tricks to make the DRV10983 a bit more sensitive for current?

    It seems we are close to some limit, because we have this problem only

    on about 10-20% of our new systems.

    Regards,

    Martin

  • 0 in reply to Martin Oppermann
    TI__Expert 3010 points

    Hi Martin,

    There is no setting available to increase current sensitivity. But we can look at cause of abnormal Kt fault and resolve it

    Can you check value of Kt during fault condition? It can be checked using GUI’s display tab.

    There is couple of ways to avoid this fault from triggering
    - Change value of ‘phase to phase Kt’ to something closer to the one calculated by DRV10983
    - Change Threshold of Kt fault by changing value of ‘abnormal Kt lock detect’ in advanced tab of GUI.

    Let me know how this goes

    Regards

    Krushal

  • 0 in reply to Krushal
    Prodigy 70 points

    Hi Krushal,

    thanks for the hints!!

    in the meantime I have made some tests and measurements.

    What I have found out is, that the value for Kt measured and calculated by the DRV10983 is going crazy in a small band of parameters.

    I my test application the motor is running with a fixed PWM value of 50, letting it run at about 800RPM at 12V with a current of about 15mA.

    If I slowly change the supply from 9V to 16V, the Kt value measured by the driver is perfectly matching the value the motor really has ( about 30mV/Hz ), except for voltages between 12V and 13V. In that supply range I can see the Kt value jumping like crazy between all possible values. And that is exactly the range, where the DRV10983 sometimes suddenly stops working with the "bad Kt" fault. I tried to calculate the mean value for the measured Kt in that range, and found out, that it is a bit lower then the "real" value. So I changed the Kt in my driver initialization to a value of 22mV/Hz. That helps a bit, but still some times the driver stops working. Especially when I let the motor run under high temperatures, when the bearings are hot and the friction is at a minimum (means less current...).


    So I wonder what is going on inside the DRV10983 with the measurement and calculation of the Kt value. The strange thing is, that there is only a small voltage band, where the chip calculates strange values. With more voltage AND with less voltage everything is ok....

    Any idea??

    best regards,

    Martin