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TMP468: BJT Selection for Temperature Sense for ~180-190 deg. C

Arijeet Saha
Prodigy 160 points
Part Number: TMP468
Other Parts Discussed in Thread: LM95172-Q1

Hi TI Team,

We have a requirement of I2C based Temperature Sensor that can measure ~180-190 deg. C. 
We can have a BJT-based remote sensing approach. 

We have selected TMP468 for our application temp. range.

We want to know that for this chipset(TMP468) if we are going with a different BJT PN. having junction temperature ~180-190 deg. C (JANTXV2N2222AUB) will that help us in our application? as Temperature Data Format (Local and Remote Temperature) Table 1 is up to 191.deg.C.


The suggested parts by TI as in the datasheet( MMBT3904 or MMBT3906) have max junction temp. as 150 deg. C.

How will that affect my performance/accuracy, η-Factor, and Offset(deg. C) value if we are going with this BJT part (JANTXV2N2222AUB) for our temperature range?

Any other suggestion/solution will be helpful.

Thanks in advance.

  • 0
    TI__Mastermind 28070 points

    Hi Arjeet,

    Thank you for your post. 

    We have tested the JANTXV2N2222AUB up to 150C, but we only recommend the device up to 125C as indicated in our Remote Temperature Transistor Selection guide. This is because the results with this transistor were very inconsistent (part-to-part) when above 125C. 

    We actually do not have any test data above 150C, as this is outside our recommended remote junction operating temperatures, and the limits of the setup we were using for this testing. We couldn't say for certain what either the TMP468, or this transistors behavior would be above that point, but given the behavior we observed, I don't think you would be able to find a single offset and N-factor setting that would produce good accuracy.

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 160 points

    Hi Brandon,
    Thanks for your reply.

    I can conclude that the TMP468 can measure a remote temperature up to max. 150 deg. C.  So, test cases are as per that only. So, for our temp. range 180-190 deg. C TMP468 is not a solution

    But in table 1, I could see data till 191 deg. C; is that only for reference?

    Please correct me if I am wrong anywhere.

    Brandon, we have a requirement of I2C based Temperature Sensor that can measure ~180-190 deg. C. 
    Can you suggest to us any solution for this temp. range?

    Thanks in advance.

  • 0 in reply to Arijeet Saha
    TI__Mastermind 28070 points

    Hi Arijeet,

    To clarify my statement, The TMP468 can display temperature higher than 150C, as you've noted, but we just don't characterize the remote diode readings above that temperature.

    We have seen with some diodes that their base emitter voltages behave non-predictably above certain temperatures, and produce strange results when used with remote temperature sensors. In theory if you could find the right transistor, it would be possible to use the TMP468 with a diode 190C. We do not calibrate the part for this temperature though, and you would still see a degradation in accuracy. 

    Arijeet Saha said:
    we have a requirement of I2C based Temperature Sensor that can measure ~180-190 deg. C. 

    We do not have any temperature sensors available with an I2C interface that would be rated for 180-190C, but we do have the LM95172-Q1 (SPI Communication), which is in a ceramic package, and rated for up to 200C. 

    Best Regards,
    Brandon Fisher