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DRV8818 Design not working!

Rahul Shah1
Prodigy 145 points
Other Parts Discussed in Thread: DRV8818

We have ordered samples of DRV8818 from TI. One of our company's application require a stepper motor driver, for which we designed the attached schematics. We will only be using the step input, whereas other inputs are permanently fixed on the hardware.

The problem I am facing is that the stepper motor rotates but not smoothly. i.e. It rotates unevenly, as if any of the coil is not energized periodically! When I check the waveforms on the outputs, I get some unclear waves on every output. I have attached my schematics. I have used 555 Timer to generate clock signal and this clock (Square wave) goes to step input of the IC.

Please check my schematics and let me know the mistake I am making or the possible cause for my issue.

2084.DRV8818 STEPPER DRIVER AND 555.pdf

  • 0 in reply to Rahul Shah1
    TI__Guru 55605 points

    Rahul,

    First of all, smoother motion can be achieved with a micro-step setting.  You are in full step mode which will be the worst in terms of smoothly moving the motor.  Try setting USM0 and USM1 to the high state. 

    By using a mode other than full-step, you will also open up full use of the adjustable decay modes.  By adjusting R9, you can tune your decay setting to receive optimum performance for your motor. 

    Finally, I don't know what your layout looks like, but this can also be a factor.  We have a low cost EVM available for $99 that includes GUI, hardware...everything you need to properly evaluate the part and eliminate layout as the source of error. 

    http://www.ti.com/tool/drv8818evm

     

  • 0 in reply to Ryan Kehr
    Prodigy 145 points

    Hi Ryan,

    Thanks for your reply.

    1. I have been driving the same stepper motor in full step mode quite smoothly using a l297 + l6203 pair from ST. Whereas with this driver I  am getting unusual movement, like it moves 3-4 steps then it stops for some time then it turns and so on. This should normally not happen even if the motor is in full step mode.

    2. I am testing the project on general purpose board, wherein I have mounted DRV8818 on SSOP to DIP PCB.

    3. If I want to use in full step mode, what should be the decay voltage?

    4. As I see in the schematics of EVM of DRV8818,  is it must to put fast recovery Schottky Diodes?