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TMP468: Reading temperature from three different ICs with integrated temperature diodes.

Ali Ghorashi
Prodigy 71 points
Part Number: TMP468

Can TMP468 be used to read the temperature from 3 different devices (one FPGA with 6 channels and two power supply ICs each with 1 channel)? Are there any concerns regarding the sharing of the D- pin between devices?

  • 0
    TI__Genius 9580 points

    Hello,

    Yes, you can use TMP468 to read temperature from 3 different devices. There is no concern regarding the sharing of D-pin between the devices. I do want to point out that there could be compatibility issues with the integrated temperature diodes for power supply ICs. The following integrated temperature diodes/transistors should follow the following:

    1. Base-emitter voltage is greater than 0.25 V when collector current is 6 μA, at the highest-sensed temperature.

    2. Base-emitter voltage is less than 0.95 V when collector current is 120 μA, at the lowest-sensed temperature.

    3. Base resistance is less than 100 Ω.

    4. Variations in h_FE are small (50 to 150).

    5. There is small lot to lot variation.

    6. η-factor is consistent across temperatures.

    For more information about what transistors are compatible with TI temperature sensors please review the following document: 

    Remote Temperature Transistor Sensor Selection Guide

    Best Regards,

    Meredith McKean

  • 0 in reply to Meredith McKean
    Prodigy 71 points

    Thank you Meredith. Are there any concerns about noise coupling into the larger loop caused by running the D- line to multiple destinations that are several inches apart? 

  • +1 in reply to Ali Ghorashi
    TI__Genius 9580 points

    Hello Ali,

    TMP468 measures very small voltages using very low currents; therefore, noise at the device inputs must be minimized. With long traces, I would recommend taking advantage of the optional series resistance and the differential capacitor for additional filtering in the device. Place the resistance as close to the the TMP468 device as possible to reduce the antenna length. 

    When choosing the resistance and competence, please follow:

    -RS < 1 kΩ (sum of both resisters)

    -CDIFF < 1000 pF

    Best Regards,

    Meredith McKean