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DRV8899-Q1: Suitable for very low current stepper motors?

Jonathan Thomson1
Prodigy 20 points
Part Number: DRV8899-Q1
Other Parts Discussed in Thread: DRV8846, DRV8847

Hello,

I am wondering if this driver would be suitable for very low current stepper motors (~20mA per coil). Specifically, the application I am looking at requires a large number of small instrumentation stepper motors (something like the X27 junken or equivalent) and the ability to daisy chain these devices over SPI is very attractive. 

I noticed in the datasheet that the open load fault can be disabled (which I am assuming would be necessary, as the open load detection threshold appears to be 30mA). If this was disabled, and VREF set to ~0.1V, could I expect the DRV8899 to drive the stepper reasonably well or should I disregard this part for my application?

Thanks,

Jonathan

  • 0
    TI__Guru 56650 points

    Jonathan,

    DRV8889 has integrated switch FETs. I have two concern with 20mA coil current regulation:

    a. The winding current mismatch. At 1.5A, the mismatch current is about +/-37.5mA which is higher than 20mA coil current value.

    b. The winding ripple current and variation could be much higher than the 20mA regulation current. In this case, it is hard to control the winding current at 20mA.

    I would select external current sense resistor stepper motor solution, such as: DRV8846...

    FYI. DRV8889 spec.

  • 0 in reply to Wang5577
    Prodigy 20 points

    Wang,

    Thanks for getting back to me and clarifying that the part is not suitable. Do you have any recommendations that would support daisy chaining, ideally over a digital bus (preferably SPI)? As I mentioned I have a large number of steppers to drive; the typical STEP/DIR interface eats through an aweful lot of IO when there are numerous motors.

    Thanks,

    Jonathan

  • 0 in reply to Jonathan Thomson1
    TI__Guru 56650 points

    Jonathan,

    You are right. the daisy chaining is good to drive multiple devices. How about I2C device DRV8847? It can save more pins and the timing control seems more easy.

    BTW, DRV8889 2.5% mismatch current is at 1.5A. When the current goes down, the percentage goes up. But, the mismatch current should be lower than 37.5mA.