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ads1244 not converting data correctly

hj
Intellectual 650 points
Other Parts Discussed in Thread: ADS1244

Hi im using the ads1244 and ive measured the input pin and the voltages are constant

But we are getting an output that keeps changing.  For example we have one the sample channels (hooked up to a mux, the Adg608) that samples a temperature sensor.  We can see with a voltmeter and with tests before that it is consistently 1.6V.  Yet now we are getting data back and it varies from 1.7V to 1.4V, which is a wide change.  Could I not be reading in the data correctly? Am I missing a bit on the spi lines?

  • 0
    TI__Guru** 113765 points

    Hi HJ,

    The transfer function is inversely proportional to the reference.  If the reference is noise, your output code will appear noisy.  If you have a poor ground, or noise related to the inputs your output code will appear noisy.  Sometimes higher frequency noise can pass through and alias back into the pass band of the ADC and your output code will appear noisy.

    One of the first things to do is narrow down the possibilities.  Disconnect the source and short the inputs to the ADC.  You should see the datasheet performance.  If not, then you have an issue with the reference, supply or layout.  Make sure you have adequate supply bypassing.

    Best regards,

    Bob B