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DRV8301-RM48-KIT Noise issues

asaygl
Intellectual 390 points
Other Parts Discussed in Thread: DRV8301

When I enable the motor controller via the gui->EnableFlg of the Motorware  foc_encoder_speed example of the DRV8301 RM48 kit, I can see a periodic noise (much like the pwms) on the pins SCI_RX (DIMM 74), LIN_RX (SCIRX_Base, DIMM 43), QEPA (DIMM 40) etc., via an oscilloscope. Because of the noise, the SCI module keeps getting parity errors, thus the constant losing of packets. Do you have any suggestions for solving this noise problem of the DRV8301 RM48 kit? It only appears after I enable the motor controller by setting gui->EnableFlg.

  • 0
    TI__Intellectual 1480 points

    Hi,

    We are looking into your query and will get back to you as soon as possible .

     

    Hercules Forum support

  • 0 in reply to Hari Pendurty
    TI__Genius 13810 points

    Can you talk a little more about your setup? I think if you use the sci-usb on the ftdi chip, you should not see much noise.

    Regards,

    Haixiao

  • 0 in reply to Haixiao Weng
    Intellectual 390 points

    Hello Haixiao,

    I'm using DRV8301-RM48-KIT with the 24V/2.1A power source and the Teknic motor, both of which are from the kit. I'm posting the before and after images of the SCI pins, before setting the "gui-EnableFlg" and after setting it. Note that other pins like LINRX or QEPA have the same behavior as well. Thee is no noise in the system if the motor connections (A,B,C) are not plugged.

    Regards,

    Asa

  • 0 in reply to asaygl
    TI__Genius 13810 points

    How do you configure resistor (on the control card): R61, R68, R78, R79? Did you change them from default?

    Sounds to me that the noise is coming from the DRV8301 mother board. You may try:

    1. remove R61, R68, R78, R79,

    2. bule wire SCITX and SCI RX (from the MCU near end of those resistors) to your destination.

    Can you show me your hardware setup? for example, RM48 SCI - DIMM - DRV8301 J12 - ....

    Since we are talking about noise, I needs to know how the propagation path looks like.

    Regards,

    Haixiao 

  • 0 in reply to Haixiao Weng
    Intellectual 390 points

    I removed R61 and R68 (R78 and R79 are already removed) blue wired LINRX (from RM48 CNCD) to my destination, and used the 5th pin (GND) of J4, but I kept losing packets. Here's how the noise looks like from the blue wire when I set gui->enableFlg:

    The noise disappears when I reset gui->enableFlg (set it to zero) in which case I can once again receive valid data from SCI. The noise is related to the motor as it seems to be periodic with a period of 50 us, the period of the foc. I'm using DRV8301 RM48 Kit without any changes from default (Teknic motor, 2.1A 24V power supply, RM48 CNCD at DIMM, etc.).

  • 0 in reply to Haixiao Weng
    TI__Genius 13810 points

    Two possibilities for the noise:

    1. Ground potiential difference between J4 and the SCIRX point due to the motor current

    2. Magnetic coupling between the pwm/motor current to the SCIRX and GND loop.

    To solve that,

    1. Minimize the loop formed by SCIRX and GND

    2. Use the adjacent Ground point for SCIRX.

    Example:

    in the following picture, run a twisted wire pair (you can twist them manually) from SCIRX and GND (they are both highlighted in the picture) to your destination (SCI and GND). Remove the other ground path (e.g another wire collects the ground of drv8301 and your destination board).

  • 0 in reply to Haixiao Weng
    Intellectual 390 points

    Thanks for the help Haixiao. Unfortunately, that somehow introduced a bias for adc as it started to measure out of range values. We decided to use digital isolators for future designs. But since DRV8301 has its own current sense amplifiers and the microcontroller has adc modules, we don't want to use an external ADC converter, but we still want to isolate DRV8301's output of current amplifiers from the microcontroller. Unfortunately, we couldn't find a good solution for an analog isolator or a suggestion on using an isolated current sense module, so we asked for suggestions on Motor Drivers forum: http://e2e.ti.com/support/applications/motor_drivers/f/38/t/268752.aspx

    Thanks again,

    Asa