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Original question:

TMP235: Temperature drifts reading

TMP235: Temperature sensor

MUHAMED AJMAL C N
Prodigy 10 points
Part Number: TMP235

Hi,

I am using TMP235 for getting temperature feedback from the synchronous switch of a buck converter. The IC is giving proper readings when I tested it by heating it through an external source,  But when the converter starts operating, the IC output goes close to the supply input of 3.3V. 

  • 0
    TI__Prodigy 480 points

    Hi Muhamed,

    The TMP235 should have an output voltage proportional to the temperature - in this case the sensor would be reading above the maximum range if it has a Vout of 3.3V. You mentioned that when heating it through an external source that it is working properly which leads me to believe that there might be something with your converter that needs to be changed. Can you please attach your schematic and how the sensor is placed on your board?

    Best,

    Rooshi

  • 0 in reply to Rooshi Nagar
    Prodigy 10 points

    Hi,

    I have attached the schematic below. Also the layout snap showing where the sensor is placed with respect to the FET  

  • 0 in reply to MUHAMED AJMAL C N
    TI__Prodigy 480 points

    Hi Muhamed,

    The schematic and layout look good to me. Here are a couple of suggestions that might help:

    1. The maximum load capacitance (Cload) should be at a max of 1000pF (.001uF). Right now it looks like you have .1uF load which is likely too large.

    2. Try to add a filter with 0.1-μF capacitor and 100-Ω resistor between external supply and VDD to limit power supply noise. 

    Additionally, take a look at section 8 (Application & Implementation) and section 9 (Power Supply Recommendations) for more details. Let me know if this helps.

    Best,

    Rooshi