Intel Celeron 365 HH80552RE104512 User Manual

83

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 a 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. 
To improve the accuracy of diode based temperature measurements, a new register 

containing Thermal Diode Offset data has been added to the Celeron D processor. 

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. This Thermal Diode Offset value will be programmed in to the new diode 

correction MSR and when added to the Thermal Diode Base value can be used to 

correct temperatures read by diode based temperature sensing devices. 
If the n

trim

 value used to calculate the Thermal Diode Offset differs from the n

trim 

value 

used in a temperature sensing device, the T

error(nf)

 may not be accurate. If desired, the 

Thermal Diode Offset 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 Diode_Base value and n

trim

 used to calculate the Diode_Correction_Offset are 

listed in 

.

n

trim

Diode ideality used to calculate Diode_Offset

1.008

Diode_Base

Diode Base

0

 C

THERMDA

AL1

diode anode

THERMDC

AK1

diode cathode