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ADS1675REF: ADS1675/ADS1675REF offset

Martin Bitter
Prodigy 10 points

Part Number: ADS1675REF

Hi,

I am trying to resolve an offset issue I am seeing on the ADS1675REF eval board:

The  inputs on ADS1675REF are set up for single-ended, 0-5V input range. For the offset test -IN grounded (+IN = 2.5V, R8 = short and -IN = 0V, R7 = short).

The readout on the GUI is -2.452V, so about 48mV shy of the -2.500V I would have expect.

When the inputs are both set to 0V or 2.5V, this offset is only 3 to 4 mV.

What is causing the large offset at 0V? Can it be compensated?

Thanks for your advise.

-Martin

  • 0
    TI__Mastermind 36190 points

    Hi Martin,

    Welcome to the TI E2E Community!

    The offset voltage specification is only valid for a differential input voltage of 0.  In your case, you have a differential voltage of 2.5V, in which case you will also have a gain error.  The Gain error of the ADC is 1% max, and the EVM board has additional error of about 1% due to the input amplifier circuit.

    By connecting both inputs to the same voltage (0V, 2.5V, etc.) you have created a differential 0V at the ADC inputs.  In this case, the offset specification of 5mV max applies, which the device meets.  (3 to 4mV of error from your measurements)

    You can eliminate both initial offset and gain error by doing a system level calibration.  Please take a look at TI Precision Labs for more details on how to do this.

    https://training.ti.com/ti-precision-labs-adcs-understanding-and-calibrating-offset-and-gain-adc-systems?context=1139104-1134080

    Regards,
    Keith Nicholas
    Precision ADC Applications