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LM86: Unexpected behavior

ttd
Mastermind 8890 points

Part Number: LM86

Dear Technical Support Team,

The LM86 causes unexpected behavior.

Background and Current Situation
On a particular board using the LM86, there are cases where it only outputs 127°C or 0°C after a certain point.
Analysis shows that reasonable values (around 30°C) are obtained initially, but after a certain point, the temperature continues to rise for several seconds, ultimately reaching 127°C.
Once this abnormal state occurs, it does not automatically recover to normal operation.
Therefore, a power cycle is required to restore normal function.
The I2C waveform itself is fine; when reading 127°C, 0x7F was correctly detected.
Furthermore, measurements of all passive component values showed no errors.

Replacing the other LM86 improves normal operation.


Regarding the occurrence, it is not intermittent; it happens 100% of the time (within 5 minutes).

Q1
Have you ever encountered this phenomenon (where the correct value becomes unreadable partway through) before?

Q2
The circuit is connected as follows; is this correct?

VDD is 3.3V with a 0.1uF capacitor
D+ and D- are connected with a 2.2uF capacitor (recommended value per datasheet)
T_CRIT_An and ALERTn are pulled up to 3.3V with a 10kΩ resistor

As a side note:

Level conversion is performed using a FET between +2.5V (FPGA side) and +3.3V (LM86 side)

Best Regards,

ttd

  • 0
    TI__Genius 11060 points

    Thank you for posting your concern. This is unusual behavior, and I'm unsure what could be interfering with the temperature sensor. I have a few questions to help be debug the issue. Is the local temperature reading error, or is it just the remote temperature sensor? What are you connecting the remote channel to? What are you measuring temperature of? I know you described the schematic, but do you mind sharing the schematic with me or at least the portion with the temperature sensor? What you described for the connections are correct. Are you seeing error with the I2C communications. Can you provide screenshots of the error that you are seeing? Correct me if I'm incorrect: You replaced the LM86 with a new LM86 temperature sensor, and this seemed to fix the error temporarily?

    Best Regards,

    Meredith McKean

  • 0 in reply to Meredith McKean
    TI__Genius 11060 points

    Can you also provide the schematic portion of this statement "Level conversion is performed using a FET between +2.5V (FPGA side) and +3.3V (LM86 side)" ?

  • 0 in reply to Meredith McKean
    Mastermind 8890 points

    Hi Meredith McKean,

    Thank you for your reply.

    I will feedback you about your check list for debug.

    I requested friend to provide schematic via private message.

    Best Regards,

    ttd

  • 0 in reply to ttd
    TI__Genius 11060 points

    This sounds great! I sent you a direct email for my contacts.