SNIS189D June   2015  – June 2018 LMT01

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     LMT01 Accuracy
  3. 3 Description
    1.     2-Pin IC Temperature Sensor
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Electrical Characteristics
    6. 6.6  Electrical Characteristics - TO-92/LPG Pulse Count to Temperature LUT
    7. 6.7  Electrical Characteristics - WSON/DQX Pulse Count to Temperature LUT
    8. 6.8  Switching Characteristics
    9. 6.9  Timing Diagram
    10. 6.10 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Interface
      2. 7.3.2 Output Transfer Function
      3. 7.3.3 Current Output Conversion to Voltage
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Mounting, Temperature Conductivity, and Self-Heating
    2. 8.2 Typical Application
      1. 8.2.1 3.3-V System VDD MSP430 Interface - Using Comparator Input
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Setting the MSP430 Threshold and Hysteresis
        3. 8.2.1.3 Application Curves
    3. 8.3 System Examples
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7.3.2 Output Transfer Function

TheLMT01 outputs at minimum 1 pulse and a theoretical maximum 4095 pulses. Each pulse has a weight of 0.0625°C. One pulse corresponds to a temperature less than –50°C while a pulse count of 4096 corresponds to a temperature greater than 200°C. Note that the LMT01 is only ensured to operate up to 150°C. Exceeding this temperature by more than 5°C may damage the device. The accuracy of the device degrades as well when 150°C is exceeded.

Two different methods of converting the pulse count to a temperature value are discussed in this section. The first method is the least accurate and uses a first order equation, and the second method is the most accurate and uses linear interpolation of the values found in the look-up table (LUT) as described in Electrical Characteristics - TO-92/LPG Pulse Count to Temperature LUT.

The output transfer function appears to be linear and can be approximated by Equation 1:

Equation 1. LMT01 new_eq01_snis189.gif

where

  • PC is the Pulse Count
  • Temp is the temperature reading

Table 1 shows some sample calculations using Equation 1.

Table 1. Sample Calculations Using Equation 1

TEMPERATURE (°C) NUMBER OF PULSES
–49.9375 1
–49.875 2
–40 160
–20 480
0 800
30 1280
50 1600
100 2400
150 3200

The curve shown in Figure 23 shows the output transfer function using equation Equation 1 (blue line) and the look-up table (LUT) found in Electrical Characteristics - TO-92/LPG Pulse Count to Temperature LUT (red line). The LMT01 output transfer function as described by the LUT appears to be linear, but upon close inspection, it can be seen as truly not linear. To actually see the difference, the accuracy obtained by the two methods must be compared.

LMT01 C002_SNIS189.pngFigure 23. LMT01 Output Transfer Function

For more exact temperature readings the output pulse count can be converted to temperature using linear interpolation of the values found in Electrical Characteristics - TO-92/LPG Pulse Count to Temperature LUT.

The curves in Figure 24 and Figure 25, show the accuracy of typical units when using the Equation 1 and linear interpolation using Electrical Characteristics - TO-92/LPG Pulse Count to Temperature LUT, respectively. When compared, the improved performance when using the LUT linear interpolation method can clearly be seen. For a limited temperature range of 25°C to 80°C, the error shown in Figure 24 is flat, so the linear equation will provide good results. For a wide temperature range, TI recommends that linear interpolation and the LUT be used.

LMT01 C018_2.15V_SNIS189.png
Figure 24. LMT01 Typical Accuracy When Using First Order Equation Equation 1 – 92 Typical Units Plotted at (VP – VN) = 2.15 V
LMT01 C017_2.15V_SNIS189.png
Figure 25. LMT01 Accuracy Using Linear Interpolation of LUT Found In Electrical Characteristics - TO-92/LPG Pulse Count to Temperature LUT – 92 typical units plotted at (VP – VN) = 2.15 V