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reading ads1217 data from outside of circuit

masoud hosseini
Prodigy 60 points
Other Parts Discussed in Thread: ADS1217

Hi

I have designed a pcb to capture a differential signal by ads1217. In the first successful try I  could read a voltage that was divided by two resistors series together between Avdd and Gnd.but when I connected Ain0 and Ain1 to a similar series resistors that were supplied by external voltage and ground I just read weird values like EF F6 FF. ( both situations provided 1.7 volt for differential input of Ain0-Ain1)

  • 0
    TI__Guru** 113765 points

    Hi Masoud,

    If you look at the Absolute Maximum Ratings table on page 2 of the datasheet you will see that there is a restriction for AIN inputs to be within GND-0.5V to AVDD+0.5V.  Any input voltage that is applied must be within that voltage range.  What I have seen is when voltages are generated by AC sources, the DC ground potential can be as much as 40V (and possibly more) between the voltage sources.  You must make sure that any input voltage must be to the same reference GND as the ADS1217.  Sometimes all that is required is connecting the GNDs together between the two supplies.  To verify that the voltage is having this condition measure each of the voltages to the analog input with respect to the ADS1217 GND (AIN+ to GND and AIN- to GND.  I suspect you will find that these voltages are not within the input range of the ADS1217.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 60 points
    Hi Mr benjamin
    As always you enlightened me perfect.
    M hosseini