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LMT70, HOW CAN I AVOID SELF-HEATING?

user4460914
Prodigy 40 points
Other Parts Discussed in Thread: LMT70

Hi, recently i tried a LMT70 sensor following the instructions given by Texas in the Datasheet.

I've welded it on a simple PCB-shield with pinheaders to connect it to an Arduino UNO, welding also a 0,01uF capacitor close to the sensor between VCC and GND.

I've loaded a sketch using the  Third Order Transfer Function Best Fit as its shown in the datasheet, and it is sensing around 60ºC due to self-heating. How can I avoid this and do i need an specific configuration?

Thanks a lot. 

  • 0
    TI__Expert 7220 points
    Hello,

    Can you share your application for using the LMT70 and what accuracy you are trying to achieve?

    The temperature error you are seeing may or may not be from self heating. Can you add a 1nF capacitor between TAO and GND lines, close to the input of the ADC on the Arduino if possible. Does the temperature reading improve after this?

    -Michael Wong
  • 0 in reply to Michael Wong
    Prodigy 40 points
    We are trying to monitorize human body temperatura, with the most accuracy possible. That`s why we've chosen that sensor.
    I think it is due to self heating because when i touch it its really really hot. And measuring 60-70-80ºC at ambient temperatue so we think its imposible to have nearly 40º of noise and that why we havent put that 1nF capacitor.
  • 0 in reply to user4460914
    TI__Expert 7220 points
    Hi,

    See section 12.1.1 of the datasheet for details about self heating. From my experience the LMT70 does not get hot under normal use. I have seen it only become really hot when the LMT70 is connected incorrectly either by putting the VDD line to the GND pin and vice versa. The other cause could be a bad solder connection on the board, the LMT70 is very small and is not uncommon for bad connections to exist.

    -Michael Wong
  • 0 in reply to Michael Wong
    Prodigy 40 points
    Hi,
    Before using it I checked that there wasn´t any shortcut between the four lines. and im nearly sure i solded it well but theres no way to check it out. The reference mark its so so tiny but i found it and put the LMT70 on his right orientation from the beggining.
    I read the whole datasheet before i started, also section 12.1.1 but i dont know which is the optimum resistance at the output. We have tried to use several resistor in order to check how it reacts and we wasnt able to get good values. Does it need some GND ground to disipate more current/heat or can i just have a GND line like the one it actually has?
    Could you please check my schemes and tell me if im i doing something wrong?