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PGA900: PGA900 internal fault issue

hao Su
Intellectual 560 points
Part Number: PGA900

Hi：

We meet a strange issue that PGA900 output will be 4.85V( intenal fault output signa) when board power on  and keep be 4.85V for about 3 to 4 seconds then back to normal output 0.5V.

The AFEDIAG shou 0x66( We don't use TGAIN) when PGA900 show 4.85V. So that mean PGAIN_UV and VINP_UV has fault.

We also find a strange issue that we put oscilloprobe on VINPP trace , the bridge voltage will drop from 1.25V to 1.02V and board will output 4.85V. (The oscilloprobe is 10Mohm )

We measuer the VDD wave of board  and find that if we use a fast up 5V power, board always output normal output 0.5V. But if we use a DC supply that have 0.4s power up time , we can easy to copy issue.

Here is VDD wave.

Could you help to explain why our PGA900(BGA type) board has this issue?

Thanks

  • 0
    TI__Mastermind 24408 points

    Hao,

    Scott is the normal support engineer for this device.  He will be back tomorrow.  For now, are you following the decoupling recommendation?  The scope probe issue is strange.  If you connect a 10M resistor (or 1M) in place of the scope probe do you see a similar drop?  Do you see this drop when the supply is ramped in a "fast" manor?  Scott, should be able to offer more guidance.  

    Art

  • 0 in reply to Art Kay
    TI__Mastermind 31655 points

    Hi Hao,

    In addition to Art's questions, can you please clarify the fault output signal you are describing? Is this part of your application firmware to set the output to 4.85V when a diagnostic fault is detected?

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Intellectual 560 points

    Hi Scott & Art:

    4.85V is firmware setting for detecting bridge fault. AFEDIAG_ CFG setting is 0xFF, Bridge voltage setting is 1.25V.

    In firmware design , if AFEDIAG is not 0x44, DAC output will be 4.85V.( We don't use TGAIN)

    Then we find that AFEDIAG will be 0x66 when board power up.

    By the way, the scope probe issue is probe problem. There is no issue after we change another probe.

    We also find that some boards will have same issue even in fast power up souce. But it is much easy to copy issue when we use slow power up source.

    Here is power wave of SG single signal wave(yellow ) and AVDD wave(bule wave)  .

    Here is our VDD and bridge hardware design . 

     

    We also find a strange thing that board never output 4.85v in power on time before we do calibration. It only happen after we finish to calibration sensor and save calibration parameter in internal eeprom.

    I think AFEDIAG will not change by calibration parameter ,am I right?  PGAIN setting don't change in calibration process.

    Could you help to explain what is PGAIN_OV and PGAIN_UV? 

    Our PGAIN setting is 50V/V, but SG is very small in zero point, so it can't be bigger than PGAIN_UV voltage 0.15V.

  • 0 in reply to Scott Cummins
    Intellectual 560 points

    Hi Scott:

    We try to change AFEDAIG_CFG to 0x1C and even use external 1.25v as bridge voltage.

    but we still can see 4.85V when board power on.

    I send our source to you by mail, could you help to check it?

    Thank you

  • 0 in reply to Scott Cummins
    Intellectual 560 points

    Hi Scott:

    We try to change AFEDAIG_CFG to 0x1C and even use external 1.25v as bridge voltage.

    but we still can see 4.85V when board power on.

    I send our source to you by mail, could you help to check it?

    Thank you

  • 0 in reply to hao Su
    TI__Mastermind 31655 points

    Hi Hao,

    Typically the diagnostics bits may be set on powerup. It is best to manually clear them on startup of the firmware, and if there is a true diagnostic issue that persists the flag will be generated again. If you manually clear the diagnostic flag within the first few seconds on the power on, does it reappear?

    Currently we are not able to support firmware review through E2E. Please see this post for more information: (+) What is the E2E support model for the PGA900 and PGA970? - Sensors forum - Sensors - TI E2E support forums

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Intellectual 560 points

    Hi Scott:

    In firmware design, we always manually clear the diagnostic flag after we read the AFEDIAG. But it still show few seconds 4.85V.

    /* Read AFEDIAG flag */
    varK = AFEDIAG;
    if (0x44 ^ varK) {
    FaultDiag = 1U;
    }
    else {
    FaultDiag = 0U;
    }

    /* Clear AFEDIAG register */
    if(AFEDIAG)
    {
    AFEDIAG = 0xFF; /* Write 1 to clear it */
    }

    We have tried to change firmware to ignor the fault for 10 seconds from power on. Then the issue disappered.

    But we want to get clear what is root cause of the issue?

    Could you help to explain what is PGAIN_OV and PGAIN_UV?  How it works?

    Thanks