Datasheet
x
PCB
R
¸
¹
·
:
62.0
=
ER
T
C
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LM95233
www.ti.com
SNIS145E –AUGUST 2006–REVISED MARCH 2013
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 Intel
processors in 65 nm process, this is specified at 4.52Ω typical. The LM95233 accommodates the typical series
resistance of Intel Processor on 65 nm process. The error that is not accounted for is the spread of the
processor's series resistance, that is 2.79Ω to 6.24Ω or ±1.73Ω. The equation to calculate the temperature error
due to series resistance (T
ER
) for the LM95233 is simply:
(10)
Solving Equation 10 for R
PCB
equal to ±1.73Ω results in the additional error due to the spread in the series
resistance of ±1.07°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 10 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 LM95233.
Processor Family Transistor Equation η
T
, non-ideality Series R,Ω
min typ max
Intel Processor on 65 nm process 0.997 1.001 1.005 4.52
Processor Family Diode Equation η
D
, non-ideality Series R,Ω
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 - 3.06
1.0011 1.0021 1.0030 3.64
GHz
Pentium 4 on 90 nm process 1.0083 1.011 1.023 3.33
Intel Processor on 65 nm process 1.000 1.009 1.050 4.52
Pentium M (Centrino) 1.00151 1.00220 1.00289 3.06
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
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 LM95233 is calibrated for two non-ideality factors and series
resistance values thus supporting the MMBT3904 transistor and Intel processors on 65 nm process without the
requirement for additional trims. For most accurate measurements TruTherm BJT beta compensation mode
should be turned on when measuring the Intel processor on 65 nm 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 (T
CF
) required to compensate for a target non-ideality differing from that supported by the
LM95233.
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