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

8.2.1.2 Calculating Total System Accuracy

The voltage seen by the LM95231 also includes the IFRS voltage drop of the series resistance. The non-ideality factor, η, is the only other parameter not accounted for and depends on the diode that is used for measurement. Since ΔVBE is proportional to both η and T, the variations in η cannot be distinguished from variations in temperature. Since the non-ideality factor is not controlled by the temperature sensor, it will directly add to the inaccuracy of the sensor. For the Pentium 4 processor on 90nm process, Intel specifies a +1.19%/−0.27% variation in η from part to part when the processor diode is measured by a circuit that assumes diode equation, Equation 4, as true. As an example, assume a temperature sensor has an accuracy specification of ±0.75°C at a temperature of 65 °C (338 Kelvin) and the processor diode has a non-ideality variation of +1.19%/−0.27%. The resulting system accuracy of the processor temperature being sensed will be:

Equation 6. TACC = ± 0.75°C + (+1.19% of 338 K) = +4.76 °C

and

Equation 7. TACC = ± 0.75°C + (−0.27% of 338 K) = −1.65 °C

TrueTherm technology uses the transistor equation, Equation 5, resulting in a non-ideality spread that truly reflects the process variation which is very small. The transistor equation non-ideality spread is ±0.1% for the Pentium 4 processor on 90nm process. The resulting accuracy when using TruTherm technology improves to:

Equation 8. TACC = ±0.75°C + (±0.1% of 338 K) = ± 1.08 °C

The next error term to be discussed is that due to the series resistance of the thermal diode and printed circuit board traces. The thermal diode series resistance is specified on most processor data sheets. For the Pentium 4 processor on 90 nm process, this is specified at 3.33Ω typical. The LM95231 accommodates the typical series resistance of the Pentium 4 processor on 90 nm process. The error that is not accounted for is the spread of the Pentium's series resistance, that is 3.242Ω to 3.594Ω or +0.264Ω to −0.088Ω. The equation to calculate the temperature error due to series resistance (TER) for the LM95231 is simply:

Equation 9. GUID-736EBC0E-C59F-4563-B595-DB6E96FAF84F-low.gif

Solving Equation 9 for RPCB equal to +0.264Ω and −0.088Ω results in the additional error due to the spread in the series resistance of +0.16°C to −0.05°C. The spread in error cannot be canceled out, as it would require measuring each individual thermal diode device. This is quite difficult and impractical in a large volume production environment.

Equation 9 can also be used to calculate the additional error caused by series resistance on the printed circuit board. Since the variation of the PCB series resistance is minimal, the bulk of the error term is always positive and can simply be cancelled out by subtracting it from the output readings of the LM95231.

Processor FamilyDiode Equation ηD, non-idealitySeries R
mintypmax
Pentium III CPUID 67h11.00651.0125
Pentium III CPUID 68h/PGA370Socket/
Celeron		1.00571.0081.0125
Pentium 4, 423 pin0.99331.00451.0368
Pentium 4, 478 pin0.99331.00451.0368
Pentium 4 on 0.13 micron process, 2-3.06GHz1.00111.00211.00303.64 Ω
Pentium 4 on 90 nm process1.00831.0111.0233.33 Ω
Pentium M Processor (Centrino)1.001511.002201.002893.06 Ω
MMBT39041.003
AMD Athlon MP model 61.0021.0081.016
AMD Athlon 641.0081.0081.096
AMD Opteron1.0081.0081.096
AMD Sempron1.002610.93 Ω