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TMS320F28035: GPIO glitch during power Up.

Faraz Ahmad
Prodigy 50 points

Part Number: TMS320F28035

Hey Support,

It has been observed that GPIO pins glitch during power up. The signal in Green is probed at Microcontroller pins directly and as can be seen a small glitch is noticed before GPIO actually goes high. This small glitch voltage (of about 800mV) is causing turn ON of the transistor.

I am using TMS320F28035 in this example. GPIO pins are all pulled down.

Can anyone please explain why this is happening or is the inherent behavior and what could be the possible solution.

Thank You.

  • 0
    TI__Mastermind 30185 points

    Hello Faraz,

    Which GPIO pin are you using? Depending on the pin, the pullup disable register bit for the corresponding GPIO pin may have a different value upon reset (i.e. on power up the pullup may be disabled or enabled by default). You can check the GPyPUD register to confirm what setting is default. Since this situation is occurring at reset, I'm assuming the issue would be a conflict with the default GPIO configuration, not necessarily any configurations you set in your code.

    Best regards,

    Omer Amir

  • 0 in reply to Omer Amir
    Prodigy 50 points

    Thanks for replying.

    I am using GPIO pin 20. I have already pulled it down using GPAPUD register, still it is glitching during power ON.

  • +1 in reply to Faraz Ahmad
    TI__Mastermind 30185 points

    Hello Faraz,

    Faraz Ahmad said:
    I have already pulled it down using GPAPUD register, still it is glitching during power ON.

    What do you mean by "during power ON"? GPIO20 by default has the internal pullup enabled, not pulldown. If the issue is happening during power up (i.e. before any code is actually executed), then it does not matter the GPAPUD register configuration if it is not disabled by default. When you power the board, GPIO20 is configured to use the internal pullup resistor, so having a pulldown configuration is probably why you are seeing a glitch. If you try to use a pin like GPIO0 where the pullup is disabled by default, do you still see this issue?

    Best regards,

    Omer Amir

  • 0 in reply to Omer Amir
    Prodigy 50 points

    Dear Sir,

    In my case "During power ON" means as soon as the controller gets live. On GPIO0, there is no glitch observed. Is there any workaround to avoid the glitch on GPIO20.

    Thanks

  • +1 in reply to Faraz Ahmad
    TI__Mastermind 30185 points

    Hello Faraz,

    Faraz Ahmad said:
    In my case "During power ON" means as soon as the controller gets live.

    If what you're describing is the power-on reset, then the only configurations you can rely on are the default values, and as such you will need to use a GPIO pin that has the internal pullup disabled. GPIO20 has it enabled by default, which is likely why you're seeing a glitch when it powers up connected to a pulldown circuit while GPIO0 doesn't have this glitch.

    Faraz Ahmad said:
    Is there any workaround to avoid the glitch on GPIO20.

    Based on the testing you did, I would say no. Is there a reason you can't change the GPIO? You don't have to specifically use GPIO0, it can be any of the GPIOs which have the pullup disabled by default.

    Best regards,

    Omer Amir

  • 0 in reply to Omer Amir
    Prodigy 50 points

    Thanks Sir, You resolved my issue. I had to change the GPIO as per your instructions.