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TMP1075: TMP1075 Alert Pin Not Triggering Despite Temperature Threshold Exceeded

Saranya R
Prodigy 30 points

Part Number: TMP1075
Other Parts Discussed in Thread: TMP1827, TMP114

I am using the TMP1075 temperature sensor on an ESP32S3 device kit via I2C. I have configured the sensor as follows:

  • Alert mode: Interrpt.

  • Alert polarity: Active low

  • High temperature threshold: 27°C

  • Low temperature threshold: 0°C

  • Fault queue: 1 (trigger immediately)

My current temperature reading is 28°C, which is above the high threshold, but the ALERT pin does not change state. I have confirmed that the I2C writes to the high/low threshold registers are successful, and reading back the registers shows the correct values.

I have connected a 10k pull up resistor to the alert pin since it is open-drain. My config register read value is 0x62FF.

Is there anything else I need to do to enable the ALERT pin?

 

  • 0
    TI__Genius 11380 points

    Hello Saranya,

    Overall, you have the correct approach in reading the alert functionality from what was given. I see that you are wanting to use interrupt mode. In Interrupt mode, the alert will recover if you perform a read of any register, a successful SMBus Alert response, or a shutdown command. I see that you are attempting to use a 10k pull up resistor. This should not be a large issue, but you can attempt to lower the resistor value to 5K. I have a few questions to help debug your issue. Can you provide all values in the registers? I would like to understand what values you are entering for the High and Low temp registers to confirm the values? Can you provide a schematic of the TMP1075 device? 

    Best Regards,

    Meredith McKean

  • 0 in reply to Meredith McKean
    Prodigy 30 points

    Hello Meredith,

    Thanks for the response.

    The alert was working actually.  


    I configured the High threshold to 27°C. Since the device temperature was already above 27°C (28.5)at startup, no alert was triggered. Is this an expected behavior?

    Later, when I changed the High threshold to 30°C and manually increased the temperature (by touching the sensor), the alert was triggered correctly once the temperature crossed 30°C.

    However, I noticed that after the temperature dropped below the High threshold and then rose above it again, no further alert was generated. From the datasheet, I understand that another alert will only occur after the temperature goes below the Low threshold (0 in my case)and then exceeds the High threshold again.

    My requirement is to generate an alert each time the temperature crosses the High threshold or goes below the Low threshold, regardless of whether it has passed the opposite threshold in between.

    Could you please confirm if this behavior is configurable in the TMP1075?

  • 0 in reply to Saranya R
    TI__Genius 11380 points

    Hello Saranya,

    For the TMP1075, the low limit acts like a hysteresis. Once the device has reached the high limit the alert will not recover until the device has reached the low limit. In interrupt mode the ALERT pin remains active until the pin is cleared by one of three events: a read of any register, a successful SMBus Alert response, or a shutdown command. If you are wanting two alert limits, I would recommend a different device. TMP114 and TMP1827 have two alert functionalities with the behavior that you are looking for.

    Best Regards,

    Meredith McKean