300 Datasheet, PDF (83/95 Pages) DB Lectro Inc – SCREW TYPE SERIES

Thermal Specifications and Design Considerations
Table 32.
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 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 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 Table 32.
Thermal “Diode” n_trim and Diode_Correction_Offset
Symbol
Parameter
n_trim
Diode_Base
Diode ideality used to calculate Diode_Offset
Diode Base
1.008
0
Unit
C
Table 33.
Thermal Diode Interface
Signal Name
Land Number
THERMDA
THERMDC
AL1
AK1
Signal Description
diode anode
diode cathode
§§
Datasheet
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