Thermal Specifications and Design Considerations
accomplished using the equations listed under Table 30. 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 ntrim) will be 1.000. Given that most diodes
are not perfect, the designers usually select an ntrim value that more closely matches
the behavior of the diodes in the processor. If the processors diode ideality deviates
from that of ntrim, each calculated temperature will be offset by a fixed amount. This
temperature offset can be calculated with the equation:
Terror(nf) = Tmeasured X (1 – nactual/ntrim
)
Where Terror(nf) is the offset in degrees C, Tmeasured is in Kelvin, nactual is the measured
ideality of the diode, and ntrim is the diode ideality assumed by the temperature
sensing device.
To improve the accuracy of diode based temperature measurements, a new register
(Tdiode_Offset) has been added to processor that 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 ntrim and the actual ideality of the
particular processor will be calculated. This value (Tdiode_Offset) will be programmed in
to the new diode correction MSR and when added to the Tdiode_Base value can be used
to correct temperatures read by diode based temperature sensing devices.
If the ntrim value used to calculate Tdiode_Offset differs from the ntrim value used in a
temperature sensing device, the Terror(nf) may not be accurate. If desired, the
T
diode_Offset can be adjusted by calculating nactual and then recalculating the offset using
the actual ntrim as defined in the temperature sensor manufacturers' datasheet.
The Diode_Base value and ntrim used to calculate the Diode_Correction_Offset are
listed in Table 32.
Table 32.
Table 33.
Thermal “Diode” ntrim and Diode_Correction_Offset
Symbol
ntrim
Diode_Base
Parameter
Unit
Diode ideality used to calculate Diode_Offset
1.008
0
—
°C
Thermal Diode Interface
Signal
Description
Signal Name
Land Number
THERMDA
THERMDC
AL1
AK1
diode anode
diode cathode
§ §
84
Datasheet
INTEL [ INTEL ]
