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Original question:

ADS1263EVM-PDK: Getting a PGARAIL_N Fault

ADS1263EVM-PDK: Getting a PGARAIL_N Fault

Olivier Bergeron25
Prodigy 130 points
Part Number: ADS1263EVM-PDK
Other Parts Discussed in Thread: ADS1263

Hi,

I got the same PGARAIL_N error with my ADS1263 evalboard. The signal injected is a 20mVpp sine wave with a 1V offset. The ADC1 is set between AIN0 and AIN1. The gain is set to 1V/V. The values have been validated with the ADS1263 excel calculator and should not be near the PGA limit. I tried different offset voltage without any improvements. What am I doing wrong?

Thanks

Olivier Bergeron

  • 0
    TI__Guru* 93085 points
    Olivier,


    Because I don't have a schematic and a more detailed description of the input voltage setup, I'm not absolutely certain what is wrong. However, I would guess that the input signal is still really out of range because of how you have it hooked up.

    If you used a function generator and added a 20mVpp sine wave with a 1V offset, that's what you have at the ADC's positive input (AINP). With a gain of 1 (PGA enabled), this is in the input range of the PGA. However, I'm guessing that the ADC's negative input (AINN) is still connected to ground. The ADS1263 measures a differential signal and both the negative input and the positive input must be in the input range of the PGA. If the negative input is connected to ground, this would be outside the range of the PGA and give the fault flag.

    To make the 20mV measurement, set up the test a little differently. Use the function generator with 20mVpp, but remove the DC offset by setting it to 0V. Attach the positive lead of the function generator to AINP and the negative lead to AINN but don't ground the negative lead. Then enable the Level-Shift Voltage (VBIAS) line in the ADS1263 as described on p44 of the datasheet. This should set the DC operating point and give you a measurement of the 20mV signal.

    Hopefully that works. If it doesn't or if you have further questions, feel free to post back.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 130 points
    Joseph,

    Thank you for your quick answer. You were right, the AINN was at ground level. The source that I used had its negative polarity internally grounded. And, of course, the DC offset voltage applied only the AINP polarity, which cause the PGARAIL_N fault.

    I did not use the bias option since I use the 2.5V internal reference. The bias level shift to 2.5V (Analog supply divided by 2).

    I disconnected the source negative polarity from the ground to let it floating, which permits me to level shift the AINN polarity to 1.25V from the GND and applied the sine waveform between AINN et AINP.

    That works perfectly now.

    Thank you again

    Olivier Bergeron