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LM35 interfacing to ADC Pin

Other Parts Discussed in Thread: LM35

I studied the data sheet, but still we need few clarifications before we go for PCB layout

Project description - LM 35 (TO-92 package) is connected to the ADC pin of ATmega32 ucontroller.  

1. Is any resistor required between +5Vcc & Vcc pin of LM35, if yes then how to calculate the value of resistor?

2. Isolating or decoupling resistor - Is resistor required between Vout and ADC pin?

3. RC damper - Is RC required between Vout and Ground?

4. Ground - LM35 ground pin - Is it to be connected with Analog ground or Digital ground?

  • Hi Vijeendra,

    1. No, there is no resistor required been +5Vcc and Vcc.

    2. It depends on several factors such as the input of the ADC and the capacitance on the trace leading to the ADC. ADC's have a variety of input stages which can have a large amount of capacitance. We are not familiar with what kind of ADC or its topology on the ATmega32 but we recommend using the following setup:

    The capacitor will store the charge from the output of the LM35 part. So when the ADC samples it will pull charge from the capacitor instead of directly from the LM35. For traces with large amount of capacitance we recommend using Figures 14 and 15 from the LM35 datasheet.

    3. RC damper is not required.

    4. Analog ground.

    Let me know if you have any additional questions.

    -Michael Wong