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Relation between STEP Input Frequency and Current Chopping in various modes of Stepper Motor Operation

Siva Murugesan
Prodigy 90 points
Other Parts Discussed in Thread: DRV8824

Hi Experts,

I am a newbie to Stepper Motors with DRV. I am working on DRV 8824. The different modes that it can chop the current are Full mode, 1/2, 1/4, 1/8, 1/16, 1/32.  When 1/8, 1/16, 1/32 modes are used with lower STEP Frequency or when Full and 1/2 modes are used with Higher STEP Frequency , there is no current chopping at the output for coils. What is the reason behind it?

My aplication is to control position of the Stepper Motor with a stipulated time. The time is large and the steps to be taken is less in requirement. So I need to drive at very low frequency which I am not able to.

Also is there any other way to control using the same DRV8824?

Please help me out.

Thanks in advance.

  • TI__Guru** 114905 points
    Hi Siva,

    Can you clarify "When 1/8, 1/16, 1/32 modes are used with lower STEP Frequency or when Full and 1/2 modes are used with Higher STEP Frequency , there is no current chopping at the output for coils"?

    Does this mean there is no current or the current is higher than expected?

    Can you have scope captures of the current versus step command?
    What are AVREF/BVREF voltages and the sense resistors used?
    What are your decay mode settings?
    What are the motor parameters? (part number, R/L/V/I)
    What is your system voltage?
  • in reply to Rick Duncan
    Prodigy 90 points

    Hi Rick,

    I am not able to capture the waveform with a scope, as when a scope is connected parallel to the motor coils, there is no output from the driver. When the scope is removed normal operation of the motor contnues.

    But for microstepping modes only high frequency STEP input works and for Full and Half Step Modes only low frequency works.

    -AVREF and BVREF are 3.3V 

    -Sense Resistors: 0.3ohm

    -For any decay mode setting, the same is the result.

    -Max resistance per phase is 14.3ohm

    -Inductance: 10.35mH

    -Voltage: 12V

    -Current / Phase
    Current = Nominal 337 mA, Peak current 476 mA

    -System Voltage: 12V

  • in reply to Siva Murugesan
    TI__Guru** 114905 points
    Hi Siva,

    I suspect the current chopping setting is incorrect, causing a less than ideal sine and cosine wave.

    At VREF = 3.3V and a 0.3 Ohm resistor, the chopping current is 2.2A. The DRV8824 cannot provide this much current to the motor. First the resistance of the motor limits the current to ~830mA at 12V. Second, 2.2A is above the maximum drive current rating for the device.

    This current chopping setting should be changed to match the motor manufacturer's specification. It should be listed as rated current or rated voltage/motor resistance.

    This should provide a current waveform that the motor is expecting.

    Once the chopping current is set, there may still be problems driving the motor at high speeds. The motor is fairly high inductance and the system voltage is relatively. This prevents the current from changing quickly, limiting the motor speed.

    Having current probes helps the debug. If you can find one, please capture scope shots of the current.