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ADS125H02: Reading the temperature sensor

Dionisio Carvalho
Prodigy 30 points
Part Number: ADS125H02
Other Parts Discussed in Thread: ADS125H01

Hi all, 

How should I to convert a RDATA ( MSB , MID and LSB) in order to read the correct temperature?

From the datasheet equation =>  Temperature (°C) = [(Temperature Reading (uV) - 120,000)/390 uV/°C]+25 °C

Considering I have set all register right and the gain is 1.

I have to convert the data ( RDATA answer) to decimal and then convert to uV?

Like:  data_read * 5 ( +-2.5) / 2 ^24 ( ADC resolution 24 bits). It is right?

It is 120 or 120 thousand I have to subtract? 

Other point, the datasheet said that the status0 is optional for the RDATA, but I had to have to set the STATENB = 1 to have a meaningful answer.

Thanks for help me

VTC = (VREF • Code) / (215 • Gain)

  • 0
    TI__Mastermind 35570 points

    Hi Dionisio,

    1. Regarding the code to the temp reading, your understanding is correct. When the gain=1, the LSB=VFSR/2^Bit=(2*Vref)/2^24=(2*2.5)/2^24=298.023nV (0.298023uV).

    Temperature Reading (uV) = data_read_code * LSB. 

    Since the unit of Temperature Reading in the equation is uV and also the Temperature coefficient is uV/°C, so the typical voltage of Temperature sensor 120mV should be converted to 120,000uV, this is the reason why the 120,000 number is shown in the equation.

    Also, a software tool in the Software Development under ADS125H01 product folder on TI.com can be used for the Code-to-Voltage conversion:

    ADS125H02 Design Calculator (Rev. A)

     2. Can you please clarify about your meaningful answer also your configuration? Regarding the datasheet:

    • If you want to include STATUS0 byte during the conversion data read, the STATENB should be set to 1.
    • If you do not want to include STATUS0 byte during the conversion data read, the STATENB should be set to 0 (default).

    Regards,

    Dale

  • 0 in reply to Dale Li
    Prodigy 30 points

    Hi Dale,

    thanks for your quick answer.

    1. Well, considering the LSB = 0.298023 uV

    If my data_read_code = 7FFFFF HEX = 8388607 DEC , which is the maximmum value.

    Employing the equation Temperature = [((Temperature Reading ) - 120,000) / 390] +25°C

    Temperature = [(8388607 * 0.298023 uV) -120,000) / 390] +25 = ~ -282,68 °C ! =/

    Even if my data_read_code = 0 , the equation answer is near to -282,69!

    What am I doing/understood wrong!?

    Best Regards, 

    Dionísio 

  • 0 in reply to Dionisio Carvalho
    Prodigy 30 points

    I did not set the correct voltage reference!! 

    It was my mistake!!

    Thanks Dale!!!