DRV8825: 1M Ohm resistor on VCP

George Ioakimedes

Part Number: DRV8825
Other Parts Discussed in Thread: DRV8824, , DRV8880

In the datasheet it states "Connect a 0.1-μF 16-V ceramic capacitor and a 1-MΩ resistor to VM" yet in all of the reference designs provided this resistor is not there. What is the reason for the 1-MΩ and why isn't it even an option for any of the designs?

Along the same lines I see some designs using a 0.1uF cap across the sense resistors but in most cases it is not shown in the schematic.

over 7 years ago

0 Rick Duncan over 7 years ago

TI__Guru** 114905 points

Hi George,

Please see this post ( https://e2e.ti.com/support/applications/motor_drivers/f/38/p/522390/1908513#1908513 ) for details regarding the resistor. The post is for the DRV8824, but the concept is the same.

Adding the footprint for a 0.1uF across the sense resistor is recommended. The additional capacitor can limit the voltage spikes due to lower inductance stepper motors. Many of the EVMs have this capacitor to allow for a wide variation of motor currents.

0 Rick Duncan over 7 years ago in reply to Rick Duncan

TI__Guru** 114905 points

Corrected link above.

0 George Ioakimedes over 7 years ago in reply to Rick Duncan

Genius 4950 points

Thanks Rick, I added those back into my design. Not to hijack my own thread but I'm a bit confused on the Decay mode and how it applies to different motors. We'll be switching to this motor and I plan on experimenting with different modes but some helpful advice would be appreciated.

Thanks,

George

0 Rick Duncan over 7 years ago in reply to George Ioakimedes

TI__Guru** 114905 points

Hi George,

Decay mode can affect current regulation of the motor.

Please see the video: training.ti.com/how-automatically-tune-your-stepper-motor for a short demonstration.

The video uses the DRV8880 which has AutoTune, plus more decay modes than the DRV8825.

0 George Ioakimedes over 7 years ago in reply to Rick Duncan

Genius 4950 points

Hi Rick,

Thanks for the feedback. I actually initially looked at the DRV8880 but because of the popularity of the DRV8825 I started the design with that part. I see that the DRV8880 is almost pin compatible to the DRV8825 so I think I'll change the design to the DRV8880 to take advantage of the AutoTune capability. I had some trouble trying to blindly tune our prototype with the DRV8825 so perhaps switching to the DRV8880 will yield a better product for us.

Thanks,
George

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DRV8825: 1M Ohm resistor on VCP