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TMP390: Config resister calculation

Part Number: TMP390

Hello Expert,

I have question regarding TMP390's config resister.
In datasheet, it showed parameter setting on a lot of resisters.
However, our customer cannot use such a high accuracy  resister.
Then, I'd like to get the formula that estimate temp setting based on their selected resistor?

Best regards,
Kazuki Kuramochi

  • Hi Kuramochi-san,

    Is your customer not able to use 1% external resistors? 

    The set resistors for the TMP390 are biased via current source and internally decoded to a certain temperature threshold or trip point. We recommend 1% external resistors to ensure that intended threshold is correctly set. 

    Two consecutive measurements for the thresholds are measured upon power on reset. If these two measurements do not agree, then the channel output is set to zero and the process repeats. If you're customer cannot use 1% resistors, they run the risk of this system level fault.


  • Hi Jalen-san,

    Thank you for your swift.

    Sorry for my less of explanation.
    Customer have concern regarding not only "accuracy" but also "resolution".
    They want to use E12 series resister but data sheet require us to use E96 resister.
    Therefore, I'd like to know about how to calculate

    From your explanation, This device read the voltage on resister by "ADC" upon POR. Is this right?
    Also, I suspect that worse accuracy and resolution resistor only lead wrong  configuration value if above understanding is correct.
    However,  you said this device cannot accomplish measurement procedure  to read resister value.
    Dose it mean there is any guard band between each required resister value?

    Best regards,
    Kazuki Kuramochi

  • Kuramochi-san,

    I would say your suspicion is correct. The way the TMP390 works is that there is no interpolation between trip points. For example looking at the thresholds settings- the set point can be configured for 50°C or 52°C. There is no trip point for 51°C.

    The E12 series resistors present two problems.

    1. Some of the resistor values do not match the E96 resistors presented in TMP390 threshold setting chart.
    2. E12 resistors have a 10% tolerance.

    Due to the value of the resistor and the tolerance, the detected trip point may end up being somewhere closer to the midpoint of the defined temperature thresholds. (For example, closer to 51°C rather than the defined 50°C or 52°C.)

    From a device level, as mentioned before, the TMP390 will set the associated channel output to zero if two consecutive measurements are not matching. On a system level, this could produce an undesirable "trip".

    For these reasons, we need to recommend the customer to use the E96 resistor series with the TMP390.