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ADS1120EVM: Converting internal temperature sensor output to temperature

William Hurley
Prodigy 10 points
Part Number: ADS1120EVM
Other Parts Discussed in Thread: ADCPRO, ADS1220

Tool/software:

Hello,

I am having a bit of trouble converting the internal temperature sensor output to a temperature. Currently I have the ADS1120EVM, and I am using the ADCpro software.

Currently the output code when I am at room temperature (~21 C ), is 3142. I belive I am misunderstanding how to convert this to a temperature, as 3142*.03125 = 98 C. I just received the device so I would have thought everything would be working properly.

Thanks,

Will

  • +1
    Prodigy 10 points

    I actually was able to figure out the issue from some other forum's here. Right shift the output by 2. Here is a calculator to do that if you need: circuitdigest.com/.../bit-shift-calculator

  • 0
    TI__Expert 8140 points

    Hi Will,

    The "3142" is the decimal representation of the binary value reading from the register, which is 16-bits.

    This value in Hex corresponds to "0C46", or "0000 1100 0100 0110" in binary.

    Although the register is 16bit, the internal temperature sensor is only 14-bit, left justified:

    So only the left most 14-bits are used.

    This would make the binary value "0000 1100 0100 01", which converted to decimal is "785".

    785 * 0.3125 = ~24.5 C

    This is the temperature of the IC internal die, not necessarily the ambient temperature. 

    The ADS1220 EVM GUI is giving you the decimal representation of the register readings, it's simply not accounting for the fact that only the first 14-bits are used for the internal temperature sensor readings, and not the full 16-bit value in the register.

    You could export the data from the GUI to excel and perform the necessary bit-shifts / math to convert your readings to temperature.

    More details on the temperature sensor can be found on section "8.3.13 Temperature Sensor" of the data sheet.

    Best Regards,

    Angel