DRV8825: DRV8825 output waveform has discontinuties

Hi Reha,

Thank you for reaching out to us. 

Reha Elci said:

I am attaching a few second video of the waveform I see on the oscilloscope on the motor output pins while the motor is connected. Any guesses as to what else I can investigate to eliminate those gaps? 

I could not open the video. Would you check the file while you are uploading. 

Reha Elci said:

I have a standard bipolar stepper being driven by DRV8825 using a prebuilt bought module.

Do you use DRV8825EVM developed by TI which can be found below? 
DRV8825EVM Evaluation board | TI.com

Reha Elci said:

The STEP input is a solid 1Kz signal, set to full 1/32 microstep (though I tried with other microstep values).

Are you using DRV8825EVM GUI from : DRV8825EVM Evaluation board | TI.com

would you please let me know what is the Input voltage, Vref, decay mode and motor DCR.?

Reha Elci said:

The output waveform has discontinuities at a regular frequency. The motor is moving well (no load attached)

I am considering that you are talking about output voltage. The output voltage is PWM and changing between zero to VM value depend on the direction, microstep,  speed and decay mode.  You need to check current waveform to see whether the device is working fine or not. 

Reha Elci said:

The motor is moving well (no load attached) otherwise however it stops during those gaps (motor is clicking and holding during gaps). The gap frequency is very stable and it doesn't seem to change much with STEP frequency. The current is adjusted to specs, and the motor holds as expected with no waveform. I do not detect any issues on the power line either

I could not open the video to find out your points about the gap. 

How do you stop the motor? In general, when you stop sending step pulse the drive does not generate the output voltages, and the motor will hold in its first stable position.

Reha Elci said:

I do not have a proper motor diagram however, given the 4 leads, it was quick to identify A and B coils (though which of the coil leads are + vs - I am not sure). I checked FAULT and it is a solid high so no issues there.

The coil polarity does not matter for running the stepper motor. as long as you are sure that you choose correct lead for phase A and B. Please use continuity test to determine phase coil leads. 

Please upload the video and respond the questions above to further assist. 

Best regards, 

Mojtaba. 

Thanks very much Mojtaba. I used this sort of a board meant for 3d printers: https://www.amazon.com/HiLetgo-DRV8825-Stepper-RAMPS1-4-StepStick/dp/B01NCE3ZW1/ref=sr_1_3?crid=1212JXA223U5K&dib=eyJ2IjoiMSJ9.2Nbn9LKnnuSeqVgDWH25FY7HjUFb7GUTgMebVU91kDqm_0dBUk0iJpUhjWw-LtBoXBohqwfi2jFQcv_qLQ1j4JcohPil-Gymv_KLYhehi3vnIZ7x7afLFJwbvVgTL8wxQMzEb5KwTnNa1If4Fyh7NRaUj7_sT8fAqC-BT73ycIQFJJA-DX_Qvy2xNSwUolpHtrAD9kv9B-JHX4D1FQzpqVXOA2rDW7y6esKZ564CAfE.Jh9SYP-H3tM7ZHTRdMB4_AEp3zcPYn5cifi0CiAcuGM&dib_tag=se&keywords=drv8825&qid=1749599531&sprefix=drv8825%2Caps%2C980&sr=8-3 

The VMOT is 18V (though i 9 and 12 - same effect). I tried vref at around .2, but also tried .15 and .3 (at .3 the motor temperature rises too much). I stop the motor by stopping the STEP signal while ENABLE is low. I am attaching the video again. Please let me know if you can access it. I am not sure what the decay mode is  - these board do not expose that but online suggests that it is set to mixed. Many thanks. 

Hi Reha, 

Thank you for your question. 

Reha Elci said:

Thanks very much Mojtaba. I used this sort of a board meant for 3d printers: https://www.amazon.com/HiLetgo-DRV8825-Stepper-RAMPS1-4-StepStick/dp/B01NCE3ZW1/ref=sr_1_3?crid=1212JXA223U5K&dib=eyJ2IjoiMSJ9.2Nbn9LKnnuSeqVgDWH25FY7HjUFb7GUTgMebVU91kDqm_0dBUk0iJpUhjWw-LtBoXBohqwfi2jFQcv_qLQ1j4JcohPil-Gymv_KLYhehi3vnIZ7x7afLFJwbvVgTL8wxQMzEb5KwTnNa1If4Fyh7NRaUj7_sT8fAqC-BT73ycIQFJJA-DX_Qvy2xNSwUolpHtrAD9kv9B-JHX4D1FQzpqVXOA2rDW7y6esKZ564CAfE.Jh9SYP-H3tM7ZHTRdMB4_AEp3zcPYn5cifi0CiAcuGM&dib_tag=se&keywords=drv8825&qid=1749599531&sprefix=drv8825%2Caps%2C980&sr=8-3 

I have check this product and could not find any user manual on their webpage. TI has evaluation module for this product which can be found 
DRV8825EVM Evaluation board | TI.com . I could better assist you with this EVM if you could work with this EVM as it is designed based on TI standards and all information are available. 

Also, DRV8825 is one of our old devices. We have more new products with better functionality and features. If you can let me know your application and requirements, I could assist you to find the right product for your project. 

Reha Elci said:

The VMOT is 18V (though i 9 and 12 - same effect). I tried vref at around .2, but also tried .15 and .3 (at .3 the motor temperature rises too much)

As it is shown below the driver regulates the motor current based on the VREF value. The Ichop is determined based on the RSENSE and VREF value. I'm not familiar with the component on your module, however, it seems that VREF = 0.2 V regulate the current to ICHOP = 0.04 / RSENSE which sound to be so low current to run the motor.

The provided video shows the output voltage waveform, Would you please let me know which output is it? is it OUTA1 or OUTA2?

Please measure the current passing through the phase A in case you have current prob and prob the OUTA1 and OUTA2 pin voltages and capture it for one current cycle. 

If you do not have current prob, please prob the outA1, outA2 voltages, with nFAULT pin and capture the time that the gap is happening. 

Best regards, 

Mojtaba.