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Original question:

TMS570LC4357: Internal temperature sensor conversion when ADC reference is not 3.3V

TMS570LC4357: Internal temperature measure

Luis Solorzano
Prodigy 40 points
Part Number: TMS570LC4357


Tool/software:

Hi,

I'm trying to measure the internal temperature on TMS570LC43, I'm using a reference voltage of 3.3V and the example code from TI Application note SPNA216. I think I'm having problems with calibration because I'm getting Junction temperatures above 78°C in an aprox 22°C ambient temperature. 

My results from calibration are: 

offset = 102.0214

slope = 0.16675

These results make sense? I don't know if maybe there is a wrong configuration in the ADC driver. I'm using the default values with ADC2 Group1 discharge time of 500ns and Sample time of 1us.

Thank you!

Best regards,

  • 0
    TI__Guru 73216 points

    Hi Luis,

    I tested SPNA216 attached code on my launchpad. And for me the results are as below:

    slope = 0.174

    offset = 224.27

    Junction temperature = 28.21 at my room temperature.

    I am also suspecting your offset value is wrong. 

    Can you please share your temperature calibration data from location 0xF0080310?

    --
    Thanks & Regards,
    Jagadish.

  • 0 in reply to jagadish gundavarapu
    Prodigy 40 points

    Hi Jagadish,

    I'm sharing with you the temperature calibration data:

    Thank you!

    Best,

  • 0 in reply to Luis Solorzano
    TI__Guru 73216 points

    Hi Luis,

    I created one dummy calibration table with your calibration data as below:

    Even with that configuration also i am not getting junction temperature as 78C.

    So, i don't understand why your ADC is giving high value.

    Are you directly using "TempSensorExample" project from APP notes directly or you made any changes?

    like enabling other peripherals or using different clock configurations etc?

    --
    Thanks & Regards,
    Jagadish.

  • 0 in reply to jagadish gundavarapu
    Prodigy 40 points

    Hi Jagadish,

    No, I created a new project because when I tried to test with "TempSensorExample" I'm getting these results:

    Do you know what could be the reason?

    So, in the new project I only enabled the ADC drivers and leave everything as default. I'm going to share with you the project, so you can see the drivers settings.

    temperature_test.zip

    Thank you!

    Best,

  • 0 in reply to Luis Solorzano
    TI__Guru 73216 points

    Hi Luis,

    I understood the route cause for the issue.

    So, you are working with HDK board right?

    TMDX570LC43HDK Development kit | TI.com

    In this schematic the ADC reference voltage can be select as either 5v or 3v. Cannot choose 3.3v directly from this schematic.

    If we connect J8 jumper, then the voltage is 3v but if we didn't connect the jumper then the reference voltage is 5v.

    However, the calibration values in the OTP were designed for 3.3v not for 3v or 5v.

    So that is the reason you are getting wrong values of temperature. But i tested with launchpad where ADC reference voltage is 3.3v, so i am getting correct values.

    My suggestion is that, try to adjust the reference voltage to 3.3v by changing either R300 or R301 to get the correct results.

    --

    Thanks & regards,
    Jagadish.