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TM4C1231H6PZ: Internal Temperature Sensor Characteristics and Use

Part Number: TM4C1231H6PZ

Hello Team,

A customer I am working with has a few questions about the use of the internal temperature sensor and I wanted to check with the experts.

1. Which temperature is being measured here? Junction temperature? Case temperature?

a. What could affect this reading? They read somewhere that gpio configuration could affect this reading and my assumption is that this would be due to higher current consumption and therefore heat in the entire device depending on gpio usage. Is this correct and are there factors other than operating configurations that would affect this measurement?

2. The datasheet mentions in section 13.3.6 that one of the purposes of the sensor is "to notify the system that internal temperature is too high or low reliable operation". Are the threshold temperatures (I am assuming -40 --> 85 C based on device) something the customer needs to monitor themselves?

3. The second described purpose in section 13.3.6 is "to provide temperature measurements for calibration of the Hibernate module RTC trim value." Can you elaborate how the temperature reading would be used to adjust the RTC trim value? I am assuming this reading could be used to adjust the trim value dynamically based on the temperature characteristics of the oscillator used for the RTC but wanted to confirm understanding here.

Best Regards,

Jacob Butler

  • Hello Jacob,

    Jacob Butler said:
    Which temperature is being measured here? Junction temperature? Case temperature?

    The temperature sensor does not measure the junction temperatures, it measures the temperature of the whole die. The junction temperatures are too dependent on external factors for a simple temperature sensor to reliably measure them.

    Jacob Butler said:
    a. What could affect this reading? They read somewhere that gpio configuration could affect this reading and my assumption is that this would be due to higher current consumption and therefore heat in the entire device depending on gpio usage. Is this correct and are there factors other than operating configurations that would affect this measurement?

    Yes there is a dependency based on the voltage of a specific pin and how the ADC is configured, see this thread for the details and if there are follow-up questions I can try and elaborate further: https://e2e.ti.com/support/microcontrollers/other/f/908/p/775222/2876444#2876444

    Also, the sensor is susceptible to noise and that can impact the reading, see the following E2E thread: https://e2e.ti.com/support/microcontrollers/other/f/908/p/427716/1528404#1528404

    Of course anything that would heat the device would impact things, as would the ambient temperature, but that is the purpose of the sensor to detect those changes.

    Jacob Butler said:
    2. The datasheet mentions in section 13.3.6 that one of the purposes of the sensor is "to notify the system that internal temperature is too high or low reliable operation". Are the threshold temperatures (I am assuming -40 --> 85 C based on device) something the customer needs to monitor themselves?

    Yes, it just gives the customer the ability to add this monitoring to their system without any external components. 

    Jacob Butler said:
    3. The second described purpose in section 13.3.6 is "to provide temperature measurements for calibration of the Hibernate module RTC trim value." Can you elaborate how the temperature reading would be used to adjust the RTC trim value? I am assuming this reading could be used to adjust the trim value dynamically based on the temperature characteristics of the oscillator used for the RTC but wanted to confirm understanding here.

    You described it exactly right, it lets you get an indication of the temperature so the oscillator can be adjusted based on it's characteristics.