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TMS320F28033: RD-195 DC arc detection evaluation board, 3.3V issue

Devinda Molligoda
Intellectual 380 points
Part Number: TMS320F28033
Other Parts Discussed in Thread: SM73201, SM72240, TMS320F28335

Hi,
I am working with a TI RD-195 DC arc detection evaluation board and I was able to detect arc with the board.

After few days of working the board failed to power up showing an over current in the 6V power supply. After debugging the board I found the over current is in the 3.3V rail. (the 5V rail works fine when I removed the 3.3V LDO )

Did any one of you faced a similar problem?

Regards,

Devinda

  • 0
    TI__Expert 7885 points
    Hello Devinda,

    Sounds like there may be a short from the LDO output to GND. Have you taken resistance measurements from the output of the LDO to other points on the board? Can you use a bench supply to power the 3.3V domain and see if it works?

    Best Regards,
    Adam Dunhoft
  • 0 in reply to Adam Dunhoft
    Intellectual 380 points

    Hello Adam,

    Thanks for your reply. I have lifted the output pin of the 3.3V LDO to disconnect it from the circuit and giving the 3.3V from bench supply. ( I have two boards with the same problem, When i check Resistance from 3.3V rail to GND it measured is 9ohm and 23.4ohm in the two boards.)

    I have disconnected the following from the 3.3V rail.

    3.3V LDO

    External ADC (SM73201)

    MCU reset IC (SM72240)

    XRS pull up of the MCU 

    So now only the MCU related connections are there on the 3.3V rail. Could it be a problem in the MCU.

    Regards,

    Devinda

     

  • 0 in reply to Devinda Molligoda
    TI__Expert 7885 points
    Hello Devinda,

    When you supply the 3.3V rail with a bench supply, does the board work?

    It is possible that the MCU has been over-stressed and damaged. Do you have the ability to scope the VDDIO, VDD and XRSn pins of the MCU?

    Best Regards,
    Adam Dunhoft
  • 0 in reply to Adam Dunhoft
    Intellectual 380 points
    Hello Adam,
    I used a 200mA current limit for the bench power supply which powered the 3.3V. Now i have removed everything except VDDIO, VDD in 3.3V rail. Still i have the low resistance between 3.3V and the GND.

    Is it normal for a MCU to draw such a high current?
    Also the same problem is present in another RD-195 board. If the MCU is damaged what might have caused it? I did not do anything out of the ordinary.

    Thanks for yur help!

    Regards,
    Devinda
  • 0 in reply to Devinda Molligoda
    TI__Expert 7885 points
    Hello Devinda,

    It is not normal for the MCU to pull 200mA of current at RT with nothing running. It sounds like the MCU has been damaged.

    Damage can come from multiple things as in shorting a supply pin to GND, supplying greater voltage to any of the pins than the device can handle or even ESD.

    Best Regards,
    Adam Dunhoft
  • 0 in reply to Adam Dunhoft
    Intellectual 380 points
    Hello Adam,
    If ESD is the case will there be any signature that i could look for?

    I dont have any precaution for ESD (like wrist strap) however, I have been using the TMS320F28335 DSP for quite a while without such problems. Is F28033 less tolerant for ESD?

    Thanks!

    Devinda
  • 0 in reply to Devinda Molligoda
    TI__Expert 7885 points
    Hello Devinda,

    In your case it sounds like it was a supply issue as the VDDIO pin is shorted to GND (per your resistance measurements). It is hard to say exactly what caused this, but your process of continuity testing the pins is the best route.

    I do not think that the F28033 and F28335 will differ in ESD tolerance.

    For more information or to see if others have had the same issues with this kit, you may want to post in the Precision Data Converters forum as I believe they are the group who designed this board.

    Precision Data Converters Forum: e2e.ti.com/.../73

    Best Regards,
    Adam Dunhoft