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LM95231 Datasheet(PDF) 21 Page - Texas Instruments |
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LM95231 Datasheet(HTML) 21 Page - Texas Instruments |
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21 / 30 page  TER = RPCB x 0.62°C/ : LM95231 www.ti.com SNIS139E – FEBRUARY 2005 – REVISED MARCH 2013 (9) 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 Family Diode Equation ηD, non-ideality Series R min typ max Pentium III CPUID 67h 1 1.0065 1.0125 Pentium III CPUID 68h/PGA370Socket/ 1.0057 1.008 1.0125 Celeron Pentium 4, 423 pin 0.9933 1.0045 1.0368 Pentium 4, 478 pin 0.9933 1.0045 1.0368 Pentium 4 on 0.13 micron process, 2-3.06GHz 1.0011 1.0021 1.0030 3.64 Ω Pentium 4 on 90 nm process 1.0083 1.011 1.023 3.33 Ω Pentium M Processor (Centrino) 1.00151 1.00220 1.00289 3.06 Ω MMBT3904 1.003 AMD Athlon MP model 6 1.002 1.008 1.016 AMD Athlon 64 1.008 1.008 1.096 AMD Opteron 1.008 1.008 1.096 AMD Sempron 1.00261 0.93 Ω Compensating for Different Non-Ideality In order to compensate for the errors introduced by non-ideality, the temperature sensor is calibrated for a particular processor. Texas Instruments temperature sensors are always calibrated to the typical non-ideality and series resistance of a given processor type. The LM95231 is calibrated for two non-ideality factors and series resistance values thus supporting the MMBT3904 transistor and the Pentium 4 processor on 90nm process without the requirement for additional trims. For most accurate measurements TruTherm mode should be turned on when measuring the Pentium 4 processor on the 90nm process to minimize the error introduced by the false non-ideality spread (see Diode Non-Ideality Factor Effect on Accuracy). When a temperature sensor calibrated for a particular processor type is used with a different processor type, additional errors are introduced. Temperature errors associated with non-ideality of different processor types may be reduced in a specific temperature range of concern through use of software calibration. Typical Non-ideality specification differences cause a gain variation of the transfer function, therefore the center of the temperature range of interest should be the target temperature for calibration purposes. The following equation can be used to calculate the temperature correction factor (TCF) required to compensate for a target non-ideality differing from that supported by the LM95231. TCF = [(ηS−ηProcessor) ÷ ηS] × (TCR+ 273 K) (10) where • ηS = LM95231 non-ideality for accuracy specification • ηT = target thermal diode typical non-ideality • TCR = center of the temperature range of interest in °C The correction factor of Equation 10 should be directly added to the temperature reading produced by the LM95231. For example when using the LM95231, with the 3904 mode selected, to measure a AMD Athlon processor, with a typical non-ideality of 1.008, for a temperature range of 60 °C to 100 °C the correction factor would calculate to: TCF=[(1.003−1.008)÷1.003]×(80+273) =−1.75°C (11) Therefore, 1.75°C should be subtracted from the temperature readings of the LM95231 to compensate for the differing typical non-ideality target. Copyright © 2005–2013, Texas Instruments Incorporated Submit Documentation Feedback 21 Product Folder Links: LM95231 |
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