I am working with a speed controller for a 3-phase brushless DC motor.

That motor is taking a 6-12S li-ion battery as input. I have additional electronics that is connected to the same power source through a 5V voltage regulator. I have tried several different types of regulators but I am unhappy with the noise that it's picking up from the switching circuit of the PWM controller on the speed controller.

I am trying to either find a better suited voltage regulator, or to add filtering on the output of the voltage regulator.

As it stands I am measuring up to +/- 5V of noise on the battery when the motor is running. On the output of the regulator I am seeing up to +/- 1.5V of noise which of course is a problem for the electronics on circuit powered by the regulator.

I have not looked at the FFT on the output of the regulator yet, but I think I will do that next.


The motor controller is based on the TI DRV8301 (schematics below) That board also has an MCU for PWM generation, and currently this controlled by a development board, but eventually everything will be integrated on the same PCB, which hopefully helps.

Anyway, the motor controller board supplies 3.3V to the Nucleo board as well as 5V to a sensor (encoder).

Communication between the Nucleo board and the motor controller is proper, however communication between the Nucleo board and sensor goes south when the motor is being controlled.

Right now, my best root cause for this issue is a noisy 5V.

As you can see from the schematics, that 5V is generated by the buck regulator on the DRV8301. I knew the voltage out of the buck reg wasn't great which is why I add that low noise 5V regulator, but obviously that's not enough.

The Nucleo board is connected to the motor controller through 3.3V and GND, and the encoder has 5V and GND wired to the motor controller. I have tried a GND to the Nucleo which doesn't help. Those connections are done with dupont wire... for now.

enter image description here

enter image description here

enter image description here

enter image description here

enter image description here


edit: Also note that I have tried powering the Nucleo and Sensor with external power and tied the ground from the external power supply to the DC power supply with no success.

edit: Is the following diagram a good simplified representation of what a Star Ground arrangement would look like? i.e. a single ground trace linking the control ground to the power ground. Is it important to make this trace going as close as possible to the GND terminal? On revised design I've been working on I have a single trace joining the 2 grounds, however this trace was not directly under the (-) DC connector but more like 1.5" south.

enter image description here

  • \$\begingroup\$ Can you give any board pic or Schematic diagram? \$\endgroup\$
    – Deepak
    Oct 5, 2020 at 18:34
  • 2
    \$\begingroup\$ You may also want to improve filtering on the INPUT to the voltage regulator... \$\endgroup\$
    – user16324
    Oct 5, 2020 at 18:38
  • 2
    \$\begingroup\$ You may have long runs of too small wire shared between the motor and electronics, or you may be drawing too much power from the cells. The electronics should have their own run back to the pack connector. Provide details of your circuit, it sort of sounds like you are asking a usage question about purchased modules rather than doing actual electronic design. \$\endgroup\$ Oct 5, 2020 at 18:41
  • 1
    \$\begingroup\$ Let me add some information to the question, I'll post schematics \$\endgroup\$
    – zytra
    Oct 5, 2020 at 18:57
  • 1
    \$\begingroup\$ I added schematics for the custom DRV8301 board and some information \$\endgroup\$
    – zytra
    Oct 5, 2020 at 19:10


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.