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PWM noise on gpio - F2803x

Amr Amin
Prodigy 20 points

I'm using the HRPWM example code (F2803x - v126) on my F28035 development board. There is a pwm noise signal on some of the unused gpio pins. How do I get rid of this noise?

  • 0
    TI__Genius 15260 points

    First things I would suggest:

    If the pin is an input, enable the pull up resistor.  If this doesn't work, set it as an output and drive it high or low.  There's also a possibility it is just your scope lead picking up the noise from the neighboring pin and it is not actually present on the pin itself.

    I can't imagine there is a significant amount of noise on the pin.  What is the concern if the IO is not being used?

    Kris

  • 0 in reply to Kris Parrent
    Prodigy 20 points

    Hi,

    Thank you for your response.

    I implemented your suggestions, but unfortunately the problem remains.

    For simplicity, I only configured hrpwm1 (i.e. gpio0 and gpio1).

    1. I made the other gpio pins gpio-inputs and tried both enabling and disabling the pull-up resistor. Outcome: a square wave pwm noise (350mV pk-pk) appeared on gpio2. A similar pwm noise appeared on the other gpio pins, but the pk-pk value decreased as I measured further gpio pins. 
    2. I set the other gpio pins as outputs and forced them low.  Outcome: The pwm noise was no longer present, but there were voltage spikes at the same points in time that hrpwm1 toggled.
    3. I tried both a different scope and measuring the pins directly. Outcome: no difference.
    4. Finally, I tried a different development board. Outcome: no difference. 
    I'm using the Piccolo F28035 development board.