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TMS320F28069M: Problem with programming the MCU

Kash Olia
Genius 3215 points
Part Number: TMS320F28069M
Other Parts Discussed in Thread: TMS320F28069

Hi,

I have two TMS320F28069 MCUs that I'm not able to program on my custom boards. When I power up the board, the reset pin on the MCU becomes low while I connect it to 3.3V through a resistor. I can read 0 volt on this pin but when I remove the MCU from the board, I can read 3.3 after the resistor. This means that the reset pin got pulled down through the MCU. Does this mean the MCU is broken? because it should be a pull up channel. :(

  • 0
    TI__Mastermind 42195 points

    Kash,

    What value of Pull-up resistor are you using? Do you think you might be having a POR, BOR or even a watchdog reset? Any of these conditions can cause the device to drive this pin low.

    Regards,
    Cody

  • 0 in reply to Cody Watkins
    Genius 3215 points

    Cody,

    That's a very good point. I've never thought about it. Here is the schematic:

    The datasheet reads: "After initial device power-up, the BOR function is present on VDDIO at all times, and on VDD when the internal VREG is enabled (VREGENZ pin is tied low)." since the VREGENZ pin is grounded in my circuit, so I'm supposed to see the voltage on the VDD and VDDIO. I'm gonna test it.

    The datasheet again reads: "Both functions tie the XRS pin low when one of the voltages is below their respective trip point. Additionally, when the internal voltage regulator is enabled, an over-voltage protection circuit will tie XRS low if the VDD rail rises above its trip point." So as the results, i need to measure the voltage on VDD (which is supposed to be zero) and VDDIO (which is supposed to be 3.3v) to make sure it doesn't go to BOR. Please correct me if this is inaccurate. 

    The question is if those pins are happy, does this mean the MCU has been damaged? 

    Thanks,

  • 0 in reply to Kash Olia
    TI__Guru 57255 points

    Hi Kash,

    You mention that you're not able to program two MCUs on your custom boards.  Do you have other custom boards that work as desired?


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Genius 3215 points
    Hi Brett,
    I have ordered 3 sample boards and the test engineer is able to program only one. The other two boards have the reset pin pulled down. I requested her to measure the voltage on VDD and VDDIO to make sure the MCU is not in POR or BOR state.
  • 0 in reply to Cody Watkins
    Genius 3215 points

    Cody and Brett,
    We found the issue and fixed it.
    The problem was the capacitors used on the VDD and VDDIO pins. The tolerance was high and I guess the ripples on the pins were higher than the trip point, that's why the MCU went to POR or BOR.

    Thanks for your help,

  • 0 in reply to Kash Olia
    TI__Mastermind 42195 points

    Kash,

    That's great news! Thanks for all of the debug on your end!

    Feel free to start another post if you have any other troubles!

    Regards,
    Cody