Intel L2400 LE80539LF0282M User Manual

Datasheet

87

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 the table below

The Intel Thermal Monitor helps control the processor temperature by activating the 

TCC (Thermal Control Circuit) when the processor silicon reaches its maximum 

operating temperature. The temperature at which the Intel Thermal Monitor activates 

the TCC is not user configurable. Bus traffic is snooped in the normal manner, and 

interrupt requests are latched (and serviced during the time that the clocks are on) 

while the TCC is active.

With a properly designed and characterized thermal solution, it is anticipated that the 

TCC would only be activated for very short periods of time when running the most 

power intensive applications. The processor performance impact due to these brief 

periods of TCC activation is expected to be minor and hence not detectable. An under-

designed thermal solution that is not able to prevent excessive activation of the TCC in 

the anticipated ambient environment may cause a noticeable performance loss, and 

may affect the long-term reliability of the processor. In addition, a thermal solution that 

is significantly under designed may not be capable of cooling the processor even when 

the TCC is active continuously.

n

trim

Diode ideality used to calculate Toffset

1.01