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Original question:

28377 power sequencing

TMS320F28377D: 28377 customboard power supply problem

z c
Prodigy 40 points
Part Number: TMS320F28377D


Hi ,

I designed my own 28377d minimum system board, and it doesn’t work. I guess I have some trouble in power supply.

The minimum system board can connect to ccs and run the demo program. But after a while,problems arose.I found at first, the value between 1.2v and 3.3v was around 10k, when pass on DC, the value reduced to almost zero quickly, which means short circuit between 1.2v and 3.3v. Turn off the power and the value will slowly Restored to 10k, but the board can not connect ccs yet, which means the chip has broken.

The 3.3v and 1.2v are come from two switching power management chip separately, I try to supply 3.3v alone and supply 3.3v and 1.2v both, and have same problem at last.

Thanks & regards,

Docata

  • 0
    TI__Expert 3720 points
    Hello,
    Concerned experts have been notified of this query.
    Note that TI US office is closed today so please expect a delayed response.


    Regards
    Himanshu
  • 0
    TI__Expert 8105 points
    Docata,

    Could it be possible that some of the decoupling capacitors were mistakenly populated with resistors on your board? A visual check should not take much time as the resistors are usually black and capacitors are typically colored tan.

    Regards,
    PEter
  • 0 in reply to Peter Galicki
    Prodigy 40 points

    Hi Peter,

    I checked my board and did not found the problem you said.

    There's another phenomenon I hope helpful for find out what happened on my own board. As shown in the figure, the reset pin(XRS) pull down every 22ms,and the value of this pin was around 2.9v not 3.3v.

    Regards,

    Docata

  • 0 in reply to z c
    TI__Expert 8105 points

    Docata,

    Seeing low pulses on reset is normal behavior when the device hasn't been configured and is unplugged from the emulator. The pulses are driven from inside the chip and are caused by the watchdog. The watchdog is enabled by default and there is no software present to prevent it from timing out - thus the periodic pulses.

    Regarding your power problem, have tried another board? Are there any differences in the sympthoms?

    Regards,
    Peter

  • 0 in reply to Peter Galicki
    Prodigy 40 points
    Hi Peter,

    I realize that the the problem may caused by virtual welding. I use a new board and new chip, welding 28377's pads carefully ,and the problem seems to have been solved.

    But unfortunately, the value of the reset pin(XRS) still be low. By reading datasheet, I learned that I should use Wait mode or another boot mode for unprogrammed devices. But even change the mode to wait mode, the reset pin still be low. Can you give me some tips for this problem.

    Thank you for your patience.

    Regards,
    Docata
  • 0 in reply to z c
    TI__Expert 8105 points

    Docata,

    When you say "the reset pin still be low" do you mean that it is continuously low or is it pulsing low?

    REgards,

    PEter

  • 0 in reply to Peter Galicki
    Prodigy 40 points

    Peter,

    I mean It is continuously low, and finially I found I have made some mistake in my reset circuit.

    Thanks again.

    Docata

  • 0 in reply to z c
    TI__Expert 8105 points

    Docata,

    Thanks for the update, glad to hear that you found your problem.


    Regards,
    Peter