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ADS1278: Using ADS1x7xEVM-PDK EVM board + ADCPro : With ADS1278

Thomas Acquistapace
Prodigy 80 points
Part Number: ADS1278
Other Parts Discussed in Thread: ADCPRO,

I am using the ADS1x7xEVM-PDK EVM board + ADCPro and when the unit is set to MULTISCOPE Mode with 2.5V (Vref), High Resolution I get an offset in the resulting data collected at 128Ksps of around 75mV on a 500mVp-p signal show here

Does anyone know why this occurs. I am monitoring the input with a scope an the offset is not present.

-Tom

  • 0
    TI__Mastermind 46760 points

    Hello Thomas,

    The maximum offset should be less than 5mV and typical should be around 1mV.  Can you measure the voltage at the input to the ADS1278 (TP10 and TP9 for channel 1)?  Do all channels show this same offset?  Are the input amplifiers enabled (JP3 NOT installed)?

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0
    Prodigy 80 points

    Hello Keith 

    JP3 is not installed and the offset on each channel (I have checked ch 1 and ch2) appear the be the same from the ADCPro results. The scope is monitoring the board input. Input is single ended since the sig gen has BNC return set to its instrument "GND".     S3 is set toward the board "center"  and   S8 is set away from the PCB board "center"  

  • 0
    Prodigy 80 points

    Hello Keith 

    Looks like the offset is coming from the O'scope. When I disconnect the scope the offset (about 60mV) entirely is gone. The scope input is single end input wtih no scope probe (BNC).   

    -Tom

  • 0 in reply to Thomas Acquistapace
    TI__Mastermind 46760 points

    Hi Tom,

    Thanks for the update.  Just to be clear, when using the input on the EVM, the negative input should be connected to the EVM board ground.  The signal generator would then be connected between the positive input and the board ground (also the negative input).

    Regards,
    Keith