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ADS1220: Does the ADS1220 Excitation Current Sources IDACs Current match varies with respect to the Loading?

Komal Charan Garlapati
Prodigy 80 points
Part Number: ADS1220

We are using ADS1220 in one of our RTD applications and the datasheet mentions that the current match is +/-0.3%.

Does this value increase with the loading?

  • +1
    TI__Guru** 112725 points

    Hi Komal,

    The IDACs are constant current sources, so as long as the compliance voltage is met the current remains constant regardless of loading.  The IDAC mismatch may affect a 3-wire RTD measurements resulting in improper lead cancellation when 2 IDACs are used.  This is discussed in detail in A Basic Guide to RTD Measurements.  Look particularly at section 1.4.1 on Lead Resistance Calculation and section 1.4.2 on IDAC Current Chopping used to cancel IDAC mismatch in the measurement.

    IDAC mismatch error is affected by device temperature.  Figure 29 in the ADS1220 datasheet shows the typical response for commonly used currents over device operating temperature.

    Best regards,

    Bob B