SBOA596 May   2024 ADS124S08 , INA326 , MSPM0G3507 , OPA387 , PGA900 , REF200

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Temperature Measure
  5. 2Key Challenge to Design a Temperature Monitor
  6. 3Proposed Designs for Temperature Monitor Based NTC or RTD
    1. 3.1 Voltage Excitation
    2. 3.2 Current Excitation
    3. 3.3 Ratio Measure
    4. 3.4 Integrated Designs
  7. 4Summary
  8. 5References

2 Key Challenge to Design a Temperature Monitor

As previously mentioned, NTC and RTD was widely used in medical system and industry system for temperature measure and monitor. However, both NTC and RTD are passive elements and needs external source to excite. There mainly has two method to excite the NTC and RTD: DC voltage or DC current. the resistor vary with temperature is quite small in generally for NTC and RTD. This is especially truth for RTD. So, designer need to use big voltage or current to excite NTC and RTD for get measurable output voltage. Also, the excite current can not too big in case heating the sensor. For example, 1℃ temperature vary can cause approximately 0.39Ω resistor vary for a 100Ω at 0℃ RTD. With 0.1mA drive current, the vary voltage is approximately 0.039mV and much less than 1LSB of 12bit-ADC with 3.3V full range. While the common voltage is 10mV. So, the maximum gain is 330 for a 3.3V system. But the gain can be need approximately 1000 if engineer require 0.2℃ resolution. for defeat this challenge, TI propose several designs to help customer easy the design and get the expected result.