X6800 Datasheet, PDF (90/122 Pages) Intel Corporation – Core2 Extreme Processor

Thermal Specifications and Design Considerations
5.3
Table 33.
Thermal Diode
The processor incorporates an on-die PNP transistor where the base emitter junction is
used as a thermal "diode", with its collector shorted to ground. A thermal sensor
located on the system board may monitor the die temperature of the processor for
thermal management and fan speed control. Table 33,Table 34, and Table 35 provide
the "diode" parameter and interface specifications. Two different sets of "diode"
parameters are listed in Table 33 and Table 34. The Diode Model parameters (Table 33)
apply to traditional thermal sensors that use the Diode Equation to determine the
processor temperature. Transistor Model parameters (Table 34) have been added to
support thermal sensors that use the transistor equation method. The Transistor Model
may provide more accurate temperature measurements when the diode ideality factor
is closer to the maximum or minimum limits. This thermal "diode" is separate from the
Thermal Monitor's thermal sensor and cannot be used to predict the behavior of the
Thermal Monitor.
T_CONTROL is a temperature specification based on a temperature reading from the
thermal diode. The value for T_CONTROL will be calibrated in manufacturing and
configured for each processor. When T_DIODE is above T_CONTROL, then T_C must be at or
below T_{C_MAX} as defined by the thermal profile in Table 29; otherwise, the processor
temperature can be maintained at T_CONTROL (or lower) as measured by the thermal
diode.
Thermal “Diode” Parameters using Diode Model
Symbol
Parameter
Min
Typ
Max
Unit Notes
I_FW
Forward Bias Current
5
—
200
µA
1
n
Diode Ideality Factor
1.000
1.009
1.050
-
2, 3, 4
R_T
Series Resistance
2.79
4.52
6.24
Ω
2, 3, 5
NOTES:
1.
Intel does not support or recommend operation of the thermal diode under reverse bias.
2.
Characterized across a temperature range of 50 – 80 °C.
3.
Not 100% tested. Specified by design characterization.
4.
The ideality factor, n, represents the deviation from ideal diode behavior as exemplified by
the diode equation:
I_FW = I_S * (e ^qVD/nkT –1)
where I_S = saturation current, q = electronic charge, V_D = voltage across the diode,
k = Boltzmann Constant, and T = absolute temperature (Kelvin).
5.
The series resistance, R_T, is provided to allow for a more accurate measurement of the
junction temperature. R_T, as defined, includes the lands of the processor but does not
include any socket resistance or board trace resistance between the socket and the
external remote diode thermal sensor. R_T can be used by remote diode thermal sensors
with automatic series resistance cancellation to calibrate out this error term. Another
application is that a temperature offset can be manually calculated and programmed into
an offset register in the remote diode thermal sensors as exemplified by the equation:
T_error = [R_T * (N–1) * I_FWmin] / [nk/q * ln N]
where T_error = sensor temperature error, N = sensor current ratio, k = Boltzmann
Constant, q = electronic charge.
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Datasheet