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DRV8841: Driver Output is Jittering

Scott Ingham
Prodigy 20 points
Part Number: DRV8841
Other Parts Discussed in Thread: DRV8844, DRV8840

Hi,

I have noticed that the DRV8841 outputs have a phase jitter in the range of about 400ns and I believe it might be causing micro-stepping problems. I'm driving a 3 phase stepping motor and I need each phase to faithfully follow the input AIN and BIN PWM inputs.  I can see that one of the bridges in the part has a 3us delay from the other and can compensate for that, but the jitter of each phase seems to be random on each phase.  Please see attached video of two of the phase.

Some additional information:

1. PWM inputs look stable

2. Driver outputs jitter with and without load.

3. DRV8841 current controller is not being used.  Vref = 3.3V and Sense resistor is 0.5R.  Drive Current is 600mA - 1A

Thank you.

  • 0
    TI__Genius 14485 points

    Hi Scott,

    Can you please tell me more about the microstepping problems you are seeing?

    • What microstepping resolution are you trying to achieve?
    • What is your PWM frequency?
    • How are you connecting your motor to the outputs?
    • Do you ground the xISEN pins, or are you using a sense resistor? Do you have any kind of current feedback for this application?

    Regarding your question about jitter, another customer on E2E found better jitter performance with the DRV8844 (see post).

    We have other motor drivers in our portfolio that might be a better fit for a 3-phase stepper driver application than the DRV8841. The DRV8841 is meant to use the VREF pins and the current control feature to implement microstepping rather than PWM. Of course, this method can only be used on a 2-phase stepper. Have you considered using a BLDC driver? Check out our 3-phase stepper reference design.

  • 0 in reply to James Lockridge19
    Prodigy 20 points

    Hi James,

    Microstepping resolution is 128 step/full .

    PWM frequency is 20 KHz

    3 half bridge outputs are connected to the motor, motor winding is a WYE

    I'm using a 0.5R resistor for current sense.  After reading your post, I connected the ISEN pins to ground, but the outputs are still jittering.

    I had seen the post you mentioned above, but it was for the DRV8840 and the reason given was because of an enable de-glitching circuit.  The DRV8841 has PWM inputs and the internal current control can be effectively disabled by connection Vref to 3.3V.

    Can you tell me what is causing the jitter in my case with the DRV8841?

    I can try the DRV8844, but the footprint and board layout would have to be changed.

    Thank you,

    Scott.

  • 0 in reply to Scott Ingham
    TI__Genius 14485 points
    Scott,

    The DRV8841 has the same deglitch circuit on the PWM as the DRV8840, so that's why it has comparable jitter. If you wanted to stay with the DRV8841, the only thing I can think to do is use the current regulation feature (VREF and a DAC) to perform microstepping. However, I'm not sure if it could work well for a 3-ph stepper application.

    Moving to the DRV8844 will give you better PWM performance for the same family of parts, but I think choosing a BLDC driver would provide the best performance and ease of use.