Intel Pentium Mobile T2130 LF80539GE0361M Data Sheet

66

Datasheet

When calculating a temperature based on thermal diode measurements, a number of 

parameters must be either measured or assumed. Most devices measure the diode 

ideality and assume a series resistance and ideality trim value, although some are 

capable of also measuring the series resistance. Calculating the temperature is then 

accomplished using the equations listed under 

. In most temperature sensing 

devices, an expected value for the diode ideality is designed-in to the temperature 

calculation equation. If the designer of the temperature sensing device assumes a 

perfect diode the ideality value (also called n

trim

) will be 1.000. Given that most diodes 

are not perfect, the designers usually select an n

trim

 value that more closely matches 

the behavior of the diodes in the processor. If the processors diode ideality deviates 

from that of n

trim

, each calculated temperature will be offset by a fixed amount. This 

temperature offset can be calculated with the equation:

T

error(nf)

 = T

measured

 X (1 - n

actual

/n

trim

)

Where T

error(nf) 

is the offset in degrees C, T

measured 

is in Kelvin, n

actual

 is the measured 

ideality of the diode, and n

trim

 is the diode ideality assumed by the temperature 

sensing device. 

In order to improve the accuracy of diode based temperature measurements, a 

temperature offset value (specified as Toffset) will be programmed into a processor 

Model Specific Register (MSR) which will contain thermal diode characterization data. 

During manufacturing each processors thermal diode will be evaluated for its behavior 

relative to a theoretical diode. Using the equation above, the temperature error created 

by the difference between n

trim

 and the actual ideality of the particular processor will 

be calculated. 
If the n

trim

 value used to calculate Toffset differs from the n

trim 

value used in a 

temperature sensing device, the T

error(nf)

 may not be accurate. If desired, the Toffset 

can be adjusted by calculating n

actual 

and then recalculating the offset using the actual 

n

trim

 as defined in the temperature sensor manufacturers' datasheet.

The n

trim

 used to calculate the Diode Correction Toffset are listed in 

n

trim

Diode ideality used to calculate Toffset

1.01