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TMP112: TMP112 long conversion time

Lina Wang
Intellectual 960 points

Part Number: TMP112

hi  TI

my customer use TMP112 in their PCBA board, if they transfer the PCBA to -25 degree cryogenic box from the 25 degree, it will spend 20 minutes to get the temp value (-25 degree). spec is only have conversion time is 26ms, but haven't show any data for while we change environment temperature suddenly. below is PCBA status in the  -25 degree cryogenic box . It contains one waterproof plastic bag and one normal paper, and in innermost is PCBA. customer think 20s time is so long time for this period, is it normal ?

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  • 0
    TI__Expert 5695 points
    Hi Lina,
    Is the time that takes to detect the -25C is 20 mins or 20 secs?
    Regardless, assuming is 20 secs is a long time, even for a sudden change of temperature, by the way, is this change from 22C (room temp) to -25C? If not please clarify.
    I assume the thermal gradient is dominated by the media that is around the PCB, (bag + filling material). The best way to prove it is putting a thermal probe as a reference instrument inside the bag and repeat the experiment.

    Regards,
    Jose
  • 0 in reply to Jose Arteaga4
    Intellectual 960 points

    hi Jose,

    it is 20 mins, not 20 secs,so customer think it is so long time.

    above test environment is their real application, not only for the test, and then they get the temp value by the MCU i2c.

  • 0 in reply to Lina Wang
    TI__Mastermind 42470 points
    Hi Lina,

    Thank you for reaching out to us. I just want to clarify with you that the conversion time and thermal reponse time are two different thing. The 26ms conversion time that specified in the datasheet is the automatic conversion sequence of how long it takes to convert the temperature from ADC for each temperature result.

    Since you were placing the TMP112 inside several of waterproof layers, this is also created the insulator that allow the device to respond temperature instantly. You mentioned that your chamber environment cools down from 22°C to -25°C. This requires sometimes to ramp down to the desired temperature.

    You can verify the thermal response time by simply dip the TMP112 into your chamber without the cryogenic box or platic bag only if you are using a non-conductive fluide such as Silicone or Galden oil.

    Hope this helps. Let me know if you have further question.

    Aaron