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Original question:

ADS1120-Q1: Temperature sensor variation under immunity test

ADS1120-Q1: Temperature simulation parameters

Koshi Ninomiya
Expert 4105 points
Part Number: ADS1120-Q1

Dear Team,

My customer is evaluating the ADS1120-Q1 with K-Type Thermocouple in their system. However, there is a slight difference in temperature between the actual thermocouple contact and the temperature sensor value inside the ADS1120-Q1, and the temperature of the measurement is displayed as an error.

In order to perform the temperature simulation, could you give us information on the structure of the ADS1120-Q1 or the thermal resistance from the terminal (AIN#) to the internal temperature sensor?
To eliminate this temperature difference, their goal is to extract parameters such as pattern, via placement, board thickness, and so on by thermal simulation.
They want information as a parameter that allows heat transmitted through the board to reach the internal temperature sensor, not the self-heat generated by the component.

I look forward to your reply.
Thank you.

Best Regards,

Koshi Ninomiya

  • 0
    TI__Guru** 112905 points

    Hi Ninomiya-san,

    There may be some confusion when making the thermocouple measurements.  The ADS1120-Q1 is an ADC that converts an input voltage to a digital output code relative to the reference voltage used.  When a thermocouple is connected, the thermocouple voltage is being measured.  The voltage created by the junction of the two dissimilar metals at the end of the thermocouple will create a voltage.  The voltage is based on data collected with an ice point as the measurement junction of 0 deg C.  This data is often shown in a table, or can be calculated using specific polynomial equations.  The PCB junction where the thermocouple connects is not at 0 deg C, so this junction must be measured to compensate for the differences in temperature from 0 deg to the actual junction temperature.

    Depending on location of the ADS1120-Q1 in relation to the cold junction, it may be possible to use the internal temperature sensor measurement to calculate the thermocouple temperature.  The internal temperature sensor will actually be measuring the temperature of the IC die. As the ADS1120-Q1 is a TSSOP package as compared to other packages such as the QFN, the only attach points to the board are at the device pins and the ambient temperature of the package.  The only thermal information for the device and package is given in the ADS1120-Q1 datasheet in the Thermal Information in section 6.4.

    To adequately measure the cold junction temperature, the junction should be thermally isolated and the ADC inside the isolated area.  

    Best regards,

    Bob B