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DRV10983 - small motor but tripping out at 50%

Richard Buswell
Prodigy 130 points
Other Parts Discussed in Thread: DRV10983

I am trying to drive a 3 watt BDCM with centrifugal fan, to replace a current design which uses a Toshiba TB6575.  I am finding I cannot get the motor up to top speed - I am using the TI dev kit.  On the TI driver the DC current at max rpm is around 300mA.

Quoted motor characteristics are 

12 pole,  1.34V rms between phase at 3000 rpm ,  1.4 ohm between phases, 0.2mH between phases.

The best results I can get with the dev kit are with the following settings

Resistance 696m, Kt 6.42, T control 120u, accel current limit 3A, lock detection limit 3.2A  

The motor will run up to just over 50% then trips out.  I have tried tweaking the resistance setting, Kt, and T control - at 150uS the motor seems to run at lower current but trips at about 52% speed.  At 120uS the motor draws more current but doesn't get above 52% (but does not trip out).

The dev kit happily drives the much larger Runtian motor that came with it, so I don't see why it shouldn't drive the smaller one!

  • 0
    TI__Guru** 114905 points
    Hi Richard,

    Our experts have been contacted and should reply soon.
  • 0
    TI__Intellectual 1555 points

    Hi Richard,

    Would you follow below to see why device is tripping out?

    1. Unclick current limit from lock detection panel

    2. Unclick BEMF abnormal from lock detection panel.

    If 1 or 2 does not solve the issue, can you provide us motor winding current before device trips?

    Thanks,

    Seil

  • 0 in reply to Seil Oh
    Prodigy 130 points
    Hi Seil - thanks for you quick response. If I unclick the current limit (I had already been running with BEMF abnormal unclicked) - the motor now goes a lot faster - it gets to about 85%. When it gets to about 54% the lock 2 error light comes on - at this point the phase current is showing about .75 amp rms. At 85% the current is .85 A rms. I am taking the phase current as the sinusoidal waveform and ignoring the spikes from the PWM pulses - I'm not sure if they are artifacts as they are only on the falling edge. The control becomes a bit unstable above 50% with the motors surging a bit.
  • 0
    Prodigy 130 points
    PS - to get 85% I had the T control at 150uS
  • 0 in reply to Richard Buswell
    TI__Intellectual 1555 points
    Hi Richard,

    What it he motor speed at the 85%? Is your duty cycle 100% at 85%?

    Can you also disable acceleration current limit on current limit tab?

    Seil
  • 0 in reply to Seil Oh
    Prodigy 130 points

    Hi - just retried - maximum speed command buffer was about 73% for 100% speed command.  The maximum frequency was 1.4 KHz - which is 14,000 rpm.  Above about 50% the motor suddenly goes up to max speed and will not slow down until the speed pot is taken to zero.  (I think this is when lock 2 light goes on).  The max pwm looks to be about 80%.

  • 0 in reply to Richard Buswell
    TI__Intellectual 1555 points

    Hi Richard,

    Hi - just retried - maximum speed command buffer was about 73% for 100% speed command. 

    This might be due to close loop current limit. if you disable it you will see it goes to 100%

     The maximum frequency was 1.4 KHz - which is 14,000 rpm.  Above about 50% the motor suddenly goes up to max speed and will not slow down until the speed pot is taken to zero.  (I think this is when lock 2 light goes on).  The max pwm looks to be about 80%

    1.4KHz is pushing the device into limit. We need good number of PWM to calculate rotor position. If we don't have much resolution, current might be unstable.

    I recommend double frequency setting enable.

    Thanks,

    Seil

    Thanks,

    Seil

  • 0 in reply to Seil Oh
    Prodigy 130 points

    Thanks Seil,

    Doubling the frequency got rid of the surging - I had to increase the open loop current limit to get it to start reliably, but that is no problem.  Oops! - I hadn't spotted that 1000 Hz was the recommended max frequency.  

    I am now in the situation that I can get enough max rpm (at 1400 Hz) and the motor is controllable with the current limit unchecked.  I am still getting lock 2 coming on at about 50% - and my max rpm is at about 70%.  Lock 2 is abnormal Kt.  Any suggestions for that?  We are very nearly there!

    Richard

  • 0 in reply to Richard Buswell
    TI__Intellectual 1555 points

    Richard,

    You can change the abnormal Kt detection window by changing Abnormal Kt lock detect threshold.

    if abnormal Kt is getting fired at low RPM, please increase the open loop to close loop treshold.

    If you see abnormal KT is getting fired at middle or high RPM, you can check what KT value devcie is calculating from display tab and make change into your motor parameter.

    If you can't solve the issue with one of two options above. You might have disable abnormal Kt for your application.

    Thanks,

    Seil

  • 0 in reply to Seil Oh
    Prodigy 130 points

    Hi Seil,

    I have widened the Kt lock detect threshold to maximum.  The calculated Kt is coming in too low at high speeds, but if I lower the Kt parameter I can't get to a high enough speed.  However  I am quite happy to run with  BEMF abnormal unchecked.

    The DRV10983 is a great IC and this forum has been an invaluable help in getting it matched to our motor!

    Thanks

    Richard

  • 0 in reply to Richard Buswell
    TI__Intellectual 1555 points

    Richard,

    Thank you! Excited to hear that DRV10983 is working well in your system.

    Thanks,

    Seil