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LMT84: Vout value

Part Number: LMT84
Other Parts Discussed in Thread: LMT85

Hi 

I try to read LMT84 temperature sensor Vout 

So, I connect from LMT84 Vout  to Micom ADC Port. 

But  ADC read value is  183~184. ADC read value seem to be wrong refer to LMT84 lookup table. 

Let me know How to solve this problem ? 

Thanks  

  • Jihwan,

    What is the measured VCC voltage on the LMT85 device?

    What it the measured VOUT voltage of the LMT85 device?

    What is the ambient temperature you are testing at for this device?

    Please use a multi-meter and measure these values.

    What is the VREF voltage for the ADC?

    Then we will look at what the ADC value and see what is going on.

  • Hi Gordon

    I will check it again. Maybe temperature and Vout voltage is ok.. 

    These are my answers as your questions. Refer to as below

    What is the measured VCC voltage on the LMT85 device?

    - VCC voltage on the LMT85 device is 5V. 

    What it the measured VOUT voltage of the LMT85 device?

    - VOUT voltage of the LMT85 devic is 0.89V

    What is the ambient temperature you are testing at for this device?

    - ambient temperature is 24 degree celsius. 

    What is the VREF voltage for the ADC?

    - VREF voltage for the ADC is 5V. 

    theses are  a results of  calculation  

    ADC value  is 183

    voltage= 5.0/1023.0 * ADC value  

    voltage = 890 mV  

    temperature (24)= (1035 - voltage) / 5.5 

    If  results of  calculation has a mistake , let me know. 

    thanks

  • Jihwan,

      by my calculations, it looks to be correct.

    10 bit ADC = 1024 bits

    5V Bias / 1024 = 0.004883 per bit.

    183 bits * 0.004883 = 0.8935 Vdc

    0.89 Vdc = 82 degrees C.

    Are you expecting a different temperature?

  • Hi Gordon 

    First of all , thank you for reply. 

    Refer to  LMT84 datasheet , I think that temperature calculation equation is  Temperature = (1035 - voltage) / 5.5 . 

    https://www.ti.com/lit/ds/symlink/lmt84.pdf

    So, if  voltage  is 890mV , temperature is 26 degree C. 

    The result of temperature calculation equation is similar to my test environment temperature. 

    Best regard.