• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 82 subscribers
  • Views 663 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F28377S: Electrical noise on the DAC when I toggle GPIO bits

NEIL SINGER
Expert 1190 points

Part Number: TMS320F28377S

if I toggle GPIO0 while I use the DAC (to check my isr rate) I get significant noise on the DAC output.  Why is that?  How can I fix it so I can use both the DAC and the GPIO pins (the noise lines up with the GPIO transitions on a scope so it is clear that the source is the GPIO)?

Also, if I stop the GPIO outputs the dac works fine.

Thanks

  • 0
    TI__Mastermind 28275 points
    Hi Neil,

    GPIO activity has a minimal impact on the DAC. If you are seeing significant coupling from the GPIO to the DAC, this could be due to various setup issues such as board design, wires etc. A few questions:

    1. What board are you using. Is this a custom designed board?
    2. What device package are you using?
    3. Do you have wires running over your setup? At reasonably fast GPIO frequencies, the wires can act as an antenna and create an EMI effect.

    You can try a quick test. Disable the DAC but still toggle the GPIO and monitor the DAC output. If you still see coupling, the problem might be coming from your setup.
  • 0 in reply to Frank Ankapong
    Expert 1190 points

    Frank,

    Thank you for the reply. We are using a stock Launchpad board with no external circuitry. We use an ARB to input a voltage on the ADC and we use an oscilloscope to measure the output of the DAC pin and the GPIO pin. One oscilloscope probe is grounded to the Launchpad board. The arb is set for infinite impedance and the negative side is grounded to the Launchpad. The launchpad is supplied power over USB. The program copies the input voltage to the DAC.

    I'll try your test shortly...

    Thank you

  • 0 in reply to NEIL SINGER
    TI__Mastermind 28275 points
    Neil,

    Each scope probe should have it's own ground connected to the launchpad so each signal will have it's own ground return path.