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DRV777: Need help selecting a driver chip for unipolar 5V stepper

Paul Wang82
Prodigy 110 points
Part Number: DRV777
Other Parts Discussed in Thread: TPL7407L, DRV8805, , DRV8833C, DRV8839

Hi,

I need to run the 28 BYJ-48 stepper motor in unipolar mode with a supply voltage of 5V. This stepper is usually driven with ULN2003. However, the ULN2003 may not be the most efficient driver due to high saturation voltage. I wonder if there are more efficient choices.

Again, the stepper will be powered using 5V, and the maximum current through each coil is roughly 200mA, so each channel of the driver must be able to handle that.

I looked at the TPL7407L, which is essentially a NMOS version of the ULN2003, but it requires a COM voltage of at least 8.5V.

I looked at the DRV8805, but that also requires a 8.2V supply voltage.

I'm also considering the DRV777, however, the maximum current per channel is only 160mA. (I heard it can be paralleled for more output?)

The driver will be controlled from a microprocessor with 5V signal.

I hope you can make a suggestion on driver choice. Efficiency is important since I want to commercialize the design.

Thanks

  • 0
    TI__Guru** 114905 points
    Hi Paul,

    The DRV777 is a good choice for your application. The outputs can be paralleled, though you will need a second DRV777 to parallel 2 outputs each. If you are only driving one stepper motor with 2 DRV777, please consider paralleling 3 outputs each.


    Other options available are the DRV8833C and 2xDRV8839. The DRV8833C can be set such that one output is at 5V (no current) while the other output is at 0V, or both outputs are Hi-Z. The DRV8839 has an enable pin on each half bridge, which allows the INx pin to be set to a logic low and the ENx pin to control the current.
  • 0 in reply to Rick Duncan
    Prodigy 110 points
    Rick, thanks for your reply.

    If I parallel 3 outputs to each coil of the stepper, the current through each channel may get too low.

    On page 4 of the DRV777 data sheet, there seems to be a low limit of 95mA per channel (I_out). Is this a big deal?

    Thanks
  • 0 in reply to Paul Wang82
    TI__Guru** 114905 points
    Hi Paul,

    There is no low limit to the current. The IOUT specification is an indication of RDSon of the FET. Typically the RDSon is .4V/.140A, or 2.8 Ohms. It could be as high as .4V/.095A, or 4.2 Ohms.

    By paralleling 3 outputs, you will have about 1/3 of the RDSon of a single FET.
  • 0 in reply to Rick Duncan
    Prodigy 110 points
    Rick, do you know roughly how big of a voltage drop the DRV777 will cause if I power the 28-byj-48 stepper motor with 5V? I know for ULN2003, the saturation voltage is roughly 1V. Just wondering how much more efficient the DRV777 will be.

    Thanks
  • 0 in reply to Paul Wang82
    TI__Guru** 114905 points
    Hi Paul,

    Expect approximately (2.8Ohms/Number of outputs connected to the winding) * the current through the winding.

    For 2 outputs in parallel and 200mA, it is 280mV. For 3 outputs in parallel and 200mA, it is 190mV.