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ADS1220: Single ended measurements with AVDD as reference

Falk Richter
Prodigy 20 points
Part Number: ADS1220
Other Parts Discussed in Thread: REF3450,

Hi,

we want to measure four single-ended channels (voltage range 0 to 5V) with a gain of one and AVDD as reference. We will supply AVDD directly from a 5V reference chip (e.g. REF3450), DVDD is supplied with 3.3V.

If we set MUX[3:0] to 1000 (as an example for the first channel: AINP = AIN0, AINN = AVSS) - what is the output code for AIN0 = AVSS and for AIN0 = AVDD? (Do we lose one bit in this unipolar configuration?)

I can't find this kind of information in the datasheet and I haven't the hardware yet (to try it out) but I already want to implement the software... :o)

Thank you very much for your help in advance!

With best regards,

Falk

  • 0
    TI__Mastermind 22055 points
    Hi Falk,

    welcome to our e2e forum and thanks a lot for your interest in ADS1220.
    I am sorry that the information provided in the datasheet is not 100% clear.

    In your case you will only leverage half of the available code range of the ADC, because you are only measuring 'differentially positive' signals.
    I personally don't like to call this losing 1 bit of resolution, because the input referred noise is still the same as if you were to measure a signal that would utilize both the positive and negative code range.

    For AIN0 = AVSS the ADS1220 will output codes which are equivalent to a differential input voltage of VIN = 0V, means values close to 000000h as shown in Table 13 in the datasheet.
    For AIN0 = AVDD the ADS1220 will output codes which are equivalent to a differential input voltage of VIN = 5V, means values close to 7FFFFFh.

    Let me know if this answers your question.

    Regards,
  • 0 in reply to Joachim Wuerker
    Prodigy 20 points

    Hi Joachim,

    thank you very much for your fast feedback! Yes this answers my question.

    Have a nice day!

    Falk