• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 129 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMP432: TMP432BDGST

Corrado Corradi
Prodigy 40 points
Part Number: TMP432
Other Parts Discussed in Thread: DXP

Hi,

I'm working with TMP432 and I used the PNP 2N2907A as remote sensor with GND collector-connected. I need to sense and regolate temperature up to 175°C.

I'm looking a very high spread beetween temperature measured by TMP432 and by a thermometer, up to 10°C. 

For example with a temperature of 100°C the TMP432 read 110-112°C.

If I increase the ambient temperature at the same value of remote ambient, the internal sensor of TMP432 measure the correct temperature.

The Bfactor used is the dafault (0x25h = 08hex) and I'm working with two remote sensor that measure the same error.

Can you suggest any other programming to improve the measure.

No capacitor or series resistor is mounted on remote sensot PNP.

Thanks.

Corrado

  • 0
    TI__Mastermind 37445 points

    Hi Corrado,

    It's normal to experience temperature error in an uncalibrated remote junction. The remote junction temperature sensors (TMP4xx products) are designed to be used with a junction that has nominal N=1.008. The 2N3906 and 2N3904 as well as their surface mount variants, MMBT3904 and so on, are commonly recommended. Even within recommended models, there can be significant variation from manufacturer-to-manufacturer and even device-to-device. TI cannot account for this external variation; the datasheet specifications assume an ideal junction with constant N Factor of 1.008 (or 1, where applicable.) See https://www.ti.com/lit/sboa433 for additional information on junction characterization.

    In addition to N Factor Correction settings, the TMP432 also features Beta Compensation. The Beta Compensation addresses an issue with embedded junctions, and is not applicable to your discrete transistor. Since the Beta Compensation feature changes effective N Factor based on the detected junction, it would be best if you disabled the Beta Compensation feature in your TMP432. You can disable it by writing 0x07 to register 0x25. 

    Your observation of 110C reported at 100C actual can be used to calculate an actual N Factor of 1.035 for your junction. However, this assumes that the TMP432 was expecting N=1.008. If it were operating in low beta mode, with an expected N=1.000, this observation would indicate actual N=1.026. Both of these cases still point to a value of 0x08 that should be written to register 0x18 N Factor Correction. Please experiment with changes to the N Factor Correction register and report back.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 40 points

    OK, I will do it.

    At the moment is not mounted any filter capacitor o R series to DXP/N pins. Do you suggest to mount it to improve the behavior?

    Corrado

  • 0 in reply to Corrado Corradi
    TI__Mastermind 37445 points

    Hi Corrado,

    It is not harmful to install capacitance below the 1nF and cumulative resistance below 1kOhm. See Figure 7 and 9.

    If you suspect you have a noise problem, please examine your DXP signal with an oscilloscope and post a zoomed-in picture of the active period (about 100ms long.)  

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 40 points

    OK everything is clear.

    Thanks.

    Corrado

  • 0 in reply to Corrado Corradi
    TI__Guru* 91146 points

    Corrado  -

    Thanks for the confirmation!