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2 phase bipolar stepper motor driver

Peter Gransee
Prodigy 30 points
Other Parts Discussed in Thread: DRV8829, DRV8704, DRV8711

We are a CNC manufacturer with >20 years in the business. Previous products have used brushed motors with fairly simply FET drivers. With this new design we are looking into some radical (for us) control methods. We would like to use bipolar stepper motors vs BLDC because the price/torque figures appear better. The higher torque at the speeds we want to operate lower the carriage mass, increasing feed rate. Our motor guy has proposed an unusual commutation of the 2 phase bipolar stepper motor that has the magnetic field 90 degrees of the electrical waveform. Apparently this FOC/CV control method  is not new but finding drivers for it is still difficult. 

For awhile, we were trying to make the DRV8829 work. It can handle the commutation scheme but just cannot deliver enough current. So close. Something like that with SPI control (we are low on IO) and 12A switches at 48v would be ideal. At least a model with external fets. We are currently looking at the Allegro A3985.

Anything we may have missed?

Thank you.

  • 0
    TI__Guru** 114905 points
    Hi Peter,

    Please take a look at the DRV8704 with external FETs. The DRV8704 has the ability to drive 2 full bridges.

    The downside is you are low on IO. Have you considered an IO expander?
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    I was just looking at the 8704/8711. The 8704 would require 4 PWM per motor. That would definitely require an IO expander for 4-5 motors. Curious, when being used to drive 2 brushed motors, how is the current individually controlled for each motor? Reason I ask is that the 8704 datasheets doesn't mention stepper motors anywhere. how are the 2 phases kept in sync and balanced?

  • 0 in reply to Peter Gransee
    TI__Guru** 114905 points
    Hi Peter,

    The DRV8704 would require external circuitry to control the current individually. The torque register can be used to limit the current below a desired level (like a first level overcurrent protection).

    Any of the brushed motor drivers can be used to control steppers with the proper circuitry around it.

    The DRV8711 with internal indexer has the ability to control the current internally. It does not include FOC/CV control. It does attempt to create a current sine and cosine wave.
  • 0 in reply to Rick Duncan
    Prodigy 30 points

    Thanks for your answer!