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TMP464: N-factor Correction

igarashi kenta
Prodigy 40 points
Part Number: TMP464

Hi,

I am trying to measure the temperature inside the IC where the N-factor is about 1.03.

IC have NPN Diode-Connected Configuration.

The distance between IC and TMP464 is close. (<30mm)

If 1.03 (0xD0) is written in register ”Remote temp N-factor correction” of TMP464, a temperature lower than the outside temperature is read.

- Outside Temp : 39.1C / Read value : 31.3C

However, If no correction (0x00) is made, the value close to the ambient temperature can be read.

- Outside Temp : 39.1C / Read value : 39.5C

The change in Read value before and after the correction is close to that of Terr, so the i2c writing is performed correctly.

Should I use offset correction? How should I determine the value?

regards,

  • 0
    TI__Mastermind 35855 points

    Hi Igarashi,

    What do you believe the IC temperature to be?

    What temperature references do you have? 

    We use calibration baths for our testing. 

    Is the IC powered?

    It will likely heat itself when powered, but you are reporting a lower measurement than expected. Self-heating would cause it to read higher than expected.

    Sometimes an IC with embedded temperature junction will have ESD structures on the temperature junction pins. If these ESD structures are not powered up, they can ruin the temperature measurement. Do you see an immediate change in the reported temperature when switching between powered and unpowered? This would be an indication of these troublesome ESD structures. 

    How long has it settled at ambient before taking the measurement?

    Ideally, we would like to keep the IC powered off and let it sit for as long as possible without heat sources. It should eventually reach equilibrium with an ambient temperature measurement. The fluid of the calibration bath is a superior thermal conductor to air, and greatly enhances accuracy of these measurements. 

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 40 points

    Hi ren,

    I used calibration baths.

    I expect a temperature measurement accuracy of less than ±1 degree.

    The temperature after 30 minutes has passed since the temperature change of the IC disappeared.

    and, ICs are powered on. So there is no mistake in the measurement. 

    I'm understanding that the N-factor correction corrects the slope to the temperature. is it correct?

    regards,

  • 0 in reply to igarashi kenta
    TI__Mastermind 35855 points

    Hi Igarashi,

    Since you have a calibration bath, I would trust your result over the stated N=1.03.

    Yes, N corrects temperature slope.

    I recommend that you collect temperature readings at a couple temperatures in your operating range and report back to me. I will then calculate an N and offset (if needed) for you.

    We do not know how the stated N=1.03 was measured. N will vary with excitation current, which may have been different than the current TMP464 uses. The N may not have been measured accurately in a calibration bath. 

    N can also vary significantly from device-to-device, production lot-to-lot. You may find that other samples read closer to N=1.03. This is intrinsic error that no remote sensor can eliminate. We can only guarantee our accuracy with a reference junction. You will have to verify your embedded junction can achieve your goal of +/-1C. 

    I'm attaching a spreadsheet with some N factor equations in case you would prefer to work with them yourself.

    thanks,

    ren

    nFactor-Basic-Tuning.xlsx