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ADS1220: ADC ADS1220 interfaced with MCU which is based on SPI Protocol.

Yash Dave
Intellectual 620 points
Part Number: ADS1220

HI,

we are using ADS1220 for one of our project. 

We are implementing ADC ADS1220 interfaced with ATXMEGA128A4U which is based on SPI Protocol.

Points to be considered:

  • Data shifted out of DATA Register is MSB first
  • SETUP of ADC configuration registers , WRITING of ADC configuration registers  and READING of ADC configuration registers  done successfully
  • ADC is SET UP as Single Shot, 20 Samples per sec, Gain 1, Vref = 3.3V (External)
  • Normal Running mode with Master routine in control of the system:
    • An interrupt to sample the ADC occurs – this comes from a timer internal to the hardware that is set to fire at the sampling rate required (200msec). This interrupt call the ADC sample routine.
    • ADC Sample Routing will then:
      • Issue the START/SYNC command for a new Single Shot sample.
      • Poll the DRDY pin waiting for sample to be taken an pin go low.
      • Read the value from ADC.

 

Facing Issue in :

  • Reading the ADC counts after conversion.

For Vin = 472mV

Calculated  value is 124ED1  (Hex), Formula- Vin(2^23-1)/ Vref

                  Value seeing on Oscilloscope and inside debugger is 00654f (Hex)à the LSB 4f keeps varying.

               

Please let us know your comments.

 

  • 0
    TI__Guru** 112905 points

    Hi Yash,

    Can you give me all of the register settings being used?  Also, can you send me more detailed information as to how the input and reference are connected?  My guess is the input is single-ended and the PGA is enabled.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Intellectual 620 points

    Dear Bob,

    1. We are configuring the registers as below

    2. Right now on prototype, we are giving ADC input from power supply but in actual case it will be from bridge of pressure sensor. So do you think we should configure for single ended?

    3. Reference voltage is same as AVDD means 3.3V .

    4. PGA is disable right now but in actual case  we will enable it.

    Rgds,

  • 0 in reply to Yash Dave
    TI__Guru** 112905 points

    Hi Yash,

    There are a couple of things that are not consistent.  First, the PGA is enabled and not disabled.  The second is the internal 2.048 V reference is being used and not 3.3V (AVDD or externally supplied).  So your expected codes will be incorrect due to the reference being used. 

    You have stated that you are using an external power supply for your input, but you have not told me specifically how you have connected this external supply to the ADS1220 inputs other than you are using AIN1 and AIN2.  Using a bridge output is much different than connecting a power supply.  The bridge output common-mode will be about 1/2 of the excitation voltage.  In the case of the 3.3V excitation, the common-mode will be about 1.65V.  If you directly connect a power supply generated from an AC source (like when using a lab supply), the output measured difference may be 472 mV between the + and - outputs, but the - output may be referenced to ground.  You should measure each input with respect to ground to determine the actual common-mode.  If AIN1 to AGND measures 0V, then the input is single-ended and you must disable the PGA to get the correct measurement.

    Best regards,

    Bob B