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DRV10983 Abnormal lock detect current limit error

Neetu Garg
Prodigy 40 points
Other Parts Discussed in Thread: DRV10983

We are currently developing a 24V 40W motor integrated to DRV10983 based motor driver. We are expressing a strange issue with DR10983 giving lock detection current limit error.

We have configured the lock detection current limit threshold to be 3.2 Amps and acceleration current limit threshold to be 2 Amps. While operating the motor, it works perfectly fine till 1 Amp. However, if we further increase the motor RPM, the current trips to lower value once it reaches 1.2 Amps. The current value is monitored through the power supply display.

The faultcode register value for 0 bit (Lock0) is high. Additionally, the status register shows overcurrent error.

This motor driver is based on our internal PCB design where DRV10983 (power pad PCB design) is integrated to Atmega328 microcontroller.

Please advice the possible reason of such abnormal behaviour.

Thanks

Neetu

  • 0
    TI__Guru** 114905 points
    Hi Neetu,

    Our experts have been notified and should reply soon.
  • 0 in reply to Rick Duncan
    TI__Expert 3010 points
    Hi Neetu,

    Power supply current is not indicator of actual phase current of motor. DRV10983 monitors phase current and detects lock/overcurrent based on amplitude of phase current. Can you please monitor current flowing through phase ?

    What are the following parameters configured to for DRV10983 - motor resistance, BEMF constant, T control advance time ?
    Sometimes T control advance time needs to be tuned to operate motor at higher current, so try changing this value and see whether it helps.

    Regards,
    Krushal
  • 0 in reply to Krushal
    Prodigy 40 points

    Hi Krushal,

         We have measured the phase current through a current transformer. The phase current is roughly 2.2 Amps RMS at the onset of fault detection. Please let me know any other methodology to measure the current. We did quick calibration of the current transformer with a known current load, and accordingly measured these values.

        The motor resistance (phase to neutral) is 0.36 ohms (0.345 ohms value in the motor driver). The BEMF constant measured through a oscilloscope is 125mV/Hz (117mV/Hz input in the motor driver). We have already tried tuning T control advance but were not able to resolve the above mentioned issue. However, the optimal performance is achieved at 640us.

        My concern is the limited current range of DRV10983. The datasheet mentions about 50W power consumption with 24VDC and 2A of continuous current. In that case, our motor is currently consuming less than 30 W at the fault occurrence. Are their possible ways to redesign the motor to reduce the phase current while achieving higher wattage? Please advice. Thanks for your kind support.

    Thanks

    Neetu

     

  • 0 in reply to Neetu Garg
    TI__Expert 3010 points
    Hi Neetu,

    With 2.2 A rms (3.1 A peak) driver is atthe edge of fault detection and that explains why you are seeing overcurrent fault. Datasheet specifies Input voltage (24 V) and Output current (2 A rms), so that doesn't necessarily translate into 50 W.

    Phase current can be decreased by increasing torque constant either by increasing magnet strength, increasing number of turns or increasing wire gauge.
    Phase current = Torque/torque_constant

    I think increasing number of turns is one of the easier way to increase torque constant and decreasing phase current. Please note that increasing torque constant means decreasing maximum speed of motor. There is always tradeoff here between electrical speed and current. But mechanical speed can be increased by increasing pole counts. There are lots of decision that are needed to made and tradeoff that needs to be considered here.

    Speed = Max_voltage/torque_constant

    Let me know how it goes.

    Regards,
    Krushal
  • 0 in reply to Krushal
    Prodigy 40 points

    Hi Krushal,

          We can optimize the motor parameters to some extent. If the shaft power requirements are more than 40 W then motor would definitely consume more than 40 W of power. In that case, we require higher amperage in the motor.

           I was checking TI design guide "24-V, 50-W BLDC Motor Sinusoidal Drive for Air Purifier Fans". http://www.ti.com/lit/ug/tiduaj0a/tiduaj0a.pdf

    The test results on page 19 of this design guide states 24 V, 2.1 A and 50.4 W of power consumption. It means we are missing something on the specification of DRV10983. Is 2A RMS limit for the entire motor driver or for each phase? Is it possible to get connected with the author of this design guide or get some additional details on the test results? Thanks for your continued support.

    Thanks

    Neetu

  • 0 in reply to Neetu Garg
    TI__Expert 3010 points

    Hi Neetu,

    There is no direct relation between input power and output power for BLDC motors. Motors are inductive load, so the power-factor (cos(theta)) is not 1. 

    Total input power = inverter_efficiency *3* V(phase)rms*I(phase)rms* power-factor.

    The TIDA design has motor which is running at speed of ~80 Hz at full power so it would have BEMF constant of ~250-300 mV/Hz and that is approximately twice compare to one you have. So in order to get similar performance you would need to increase torque/BEMF constant to approximately two times.

    The amplitude of current for any motor depends on torque which includes load torque, fiction torque, damping torque and other losses in motor. 

    Regards,

    Krushal