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ADS1120: ADS1120 SPI data error when - value -> + value

IKJAE JANG
Prodigy 30 points
Part Number: ADS1120

Hi experts!

I am developing a K-type thermocouple project using the ADS1120.

The register is set properly and it is working well.

When the thermoelectric voltage value was compensated with the internal temperature sensor, the exact value also came out.

But...

there is one problem that is too difficult for me....

1. At room temperature, the SPI data(2bytes) value is [0] 0xFF, [1] 0x**]

2. When I hold the thermocouple by hand, the temperature rises and the SPI data value rises.  [0] 0x00, [1] 0x**

3. The problem is that the SPI action dies at the moment it changes from a negative value to a positiva value.

What should I check? :(

  • 0
    Prodigy 30 points

    My sequence is :

    - Init ------------------------------------------------

    (1) Register 0~3 set 0x0A/0x02/0x10/0x00 : ANIP=ANI0, ANIN=ANI1, PGA=32, 20SPS, single conversion, Internal Temp enabled

    (2) Internal Temp sensor data acquisition : ex) room temperature 25'C

    (3) Register 1 set 0x04 : continuous mode

    -DRDY interrupt ----------------------------------

    (4) Thermocouple data acquisition  20sps 

  • 0 in reply to IKJAE JANG
    TI__Guru** 113765 points

    Hi Ikjae,

    Welcome to the E2E forum!  Can you explain in more detail by what you mean when you say the "SPI action dies"?  Does this mean the microprocessor is no longer sending SCLKs?  How are you determining when to read the data?  Are you monitoring DRDY?  Have you checked DRDY to make sure that it is still toggling every 50ms (20sps) with an oscilloscope or logic analyzer?

    Do you have a schematic that you can send me?  It is possible that a transient event has occurred when you touch the TC and it either halts the micro or the ADS1120.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    Hi Ikjae,

    I have not heard anything back from you and I was wondering if you solved your issue?  If not, reply back or if you have additional questions feel free to create a new post.

    Best regards,

    Bob B