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LM135A: Can't set up temperature sensor

ArTzy
Genius 15639 points
Part Number: LM135A
Other Parts Discussed in Thread: LM135

Hi Experts,

Good day. I have this query from a client who is having hard time trying to set up the analog device temperature sensor - LM135A. Below is there full query.

"We are working on a project to use a temperature sensor to measure the temperature of components on a computing device. We have read the entire data sheet and are still unable to understand how to create one with the given information. Can you please provide an explanation or at least the Steinhart–Hart equation coefficients A and B and C for the thermistor and the resistance of the thermistor. We are unable to calibrate these coefficients because in order to do so we need the running temperature of the LM135A to do which would require us to have a temperature sensor which we do not have."

I found THIS article but seems that it couldn't help them. Can you help us with this regard?

Thank you.

Regards,
Archie A.

  • 0
    TI__Mastermind 40985 points

    Hi Archie,

    LM135A reports temperature 10mV per kelvin. If 2.98V is observed, you only need to multiply this number by 100 to know the temperature is 298K. To convert kelvin to celsius, subtract 273.15. As shown in the spec table, 298K is room temperature or about 25C. There's no need to use a thermistor or Steinhart equations with LM135A. 

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    TI__Genius 15639 points

    Hello Ren,

    I received additional query from individual who is trying to interact with this post but unable to.

    He is okay with using the linear equation that TI provided. But to get a 2.98V output, what would the required voltage input be and the required resistance bias needed? The manual is not clear for what these values should be to get this required output

    Hoping for your guidance on this.

    Thank you.

    Regards,
    Archie A.

  • 0 in reply to ArTzy
    TI__Mastermind 40985 points

    Archie,

    8.2.2 Detailed Design Procedure

    For optimum accuracy, R1 is picked such that 1 mA flows through the sensor. Additional error can be introduced by varying load currents or varying supply voltage. The influence of these currents on the minimum and maximum reverse current flowing through the LM135 should be calculated and be maintained in the range of 0.4 mA to 5 mA. Minimizing the current variation through the LM135 will provide for the best accuracy. The Operating Output Voltage Change with Current specification can be used to calculate the additional error which could be up to 1 K maximum from the LM135A, for example.

    If the customer needs help calculating R1, please let me know the supply voltage they intend to use.

    thanks,

    ren