SNIS139F February   2005  – January 2024 LM95231

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 Operating Ratings
    3. 5.3 Temperature-to-Digital Converter Characteristics
    4. 5.4 Logic Electrical Characteristics Digital DC Characteristics
    5. 5.5 Logic Electrical Characteristics SMBus Digital Switching Characteristics
    6. 5.6 Typical Performance Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Conversion Sequence
      2. 6.3.2 Power-On-Default States
      3. 6.3.3 SMBus Interface
      4. 6.3.4 Temperature Data Format
      5. 6.3.5 SMBDAT Open-Drain Output
      6. 6.3.6 Diode Fault Detection
      7. 6.3.7 Communicating with the LM95231
      8. 6.3.8 Serial Interface Reset
      9. 6.3.9 One-Shot Conversion
  8. 7 Registers
    1. 7.1 LM95231 Registers
    2. 7.2 Status Register
    3. 7.3 Configuration Register
    4. 7.4 Remote Diode Filter Control Register
    5. 7.5 Remote Diode Model Type Select Register
    6. 7.6 Remote TruTherm Mode Control
    7. 7.7 Local and Remote MSB and LSB Temperature Registers
      1. 7.7.1 Local Temperature MSB
      2. 7.7.2 Local Temperature LSB
      3. 7.7.3 Remote Temperature MSB
      4. 7.7.4 Remote Temperature LSB
    8. 7.8 Manufacturers ID Register
    9. 7.9 Die Revision Code Register
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Diode Non-Ideality
        1. 8.2.1.1 Diode Non-Ideality Factor Effect on Accuracy
        2. 8.2.1.2 Calculating Total System Accuracy
        3. 8.2.1.3 Compensating for Different Non-Ideality
  10. 9 Layout
    1. 9.1 PCB Layout for Minimizing Noise
  11. 10Device and Documentation Support
    1. 10.1 Documentation Support
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.1.1 Diode Non-Ideality Factor Effect on Accuracy

When a transistor is connected as a diode, the following relationship holds for variables VBE, T and IF:

Equation 1. GUID-8047FE9C-F211-4922-A07B-D917165A1682-low.gif

where

  • GUID-692AB39F-99B9-4284-8A27-5C73297755A0-low.gif
  • q = 1.6×10−19 Coulombs (the electron charge),
  • T = Absolute Temperature in Kelvin
  • k = 1.38×10−23joules/K (Boltzmann's constant),
  • η is the non-ideality factor of the process the diode is manufactured on,
  • IS = Saturation Current and is process dependent,
  • If= Forward Current through the base emitter junction
  • VBE = Base Emitter Voltage drop

In the active region, the -1 term is negligible and may be eliminated, yielding the following equation

Equation 2. GUID-8F160DA1-2855-418A-88E8-B059F98F86A1-low.gif

In Equation 2,  η and IS are dependant upon the process that was used in the fabrication of the particular diode. By forcing two currents with a very controlled ratio (IF2/IF1) and measuring the resulting voltage difference, it is possible to eliminate the IS term. Solving for the forward voltage difference yields the relationship:

Equation 3. GUID-E3C603F6-5579-4F95-A385-B1C7C2FB8692-low.gif

Solving Equation 3 for temperature yields:

Equation 4. GUID-B3FC129A-C35F-4C2D-AF73-5282A86CDB73-low.gif

Equation 4 holds true when a diode connected transistor such as the MMBT3904 is used. When this “diode” equation is applied to an integrated diode such as a processor transistor with its collector tied to GND as shown in Figure 8-1 it will yield a wide non-ideality spread. This wide non-ideality spread is not due to true process variation but due to the fact that Equation 4 is an approximation.

TruTherm technology uses the transistor equation, Equation 5, which is a more accurate representation of the topology of the thermal diode found in an FPGA or processor.

Equation 5. GUID-668C1949-F1E3-4EFB-9596-F57051B11E10-low.gif
GUID-1C66CBD1-DF52-4DD6-9C5A-AB783AB1D454-low.gifFigure 8-1 Thermal Diode Current Paths

TruTherm should only be enabled when measuring the temperature of a transistor integrated as shown in the processor of Figure 8-1, because Equation 5 only applies to this topology.