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Thermal Specifications and Design Considerations
Table 25.
Thermal Diode Parameters Using Transistor Model
Symbol
I
FW
I
E
n
Q
Beta
R
T
NOTES:
1.
Intel does not support or recommend operation of the thermal diode under reverse bias.
2.
Same as I
3.
Characterized across a temperature range of 50-100°C.
4.
Not 100% tested. Specified by design characterization.
5.
The ideality factor, nQ, represents the deviation from ideal transistor model behavior as
exemplified by the equation for the collector current:
where I
base emitter junction (same nodes as VD), k = Boltzmann Constant, and T = absolute
temperature (Kelvin).
6.
The series resistance, R
more accurate readings as needed.
When calculating a temperature based on the 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 are capable of
also measuring the series resistance. Calculating the temperature is then accomplished
using the equations listed under
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
usually select an n
the processor. If the processor diode ideality deviates from that of the n
calculated temperature offsets by a fixed amount. This temperature offset can be
calculated with the equation:
where T
error(nf)
ideality of the diode, and n
sensing device.
5.1.2
Thermal Diode Offset
In order to improve the accuracy of the diode-based temperature measurements, a
temperature offset value (specified as Toffset) is programmed in the processor MSR
which contains thermal diode characterization data. During manufacturing each
processor thermal diode is evaluated for its behavior relative to the theoretical diode.
Using the equation above, the temperature error created by the difference n
actual ideality of the particular processor is calculated.
Datasheet
Parameter
Forward Bias Current
Emitter Current
Transistor Ideality
Series Resistance
in
Table
24.
FW
qV
/n
kT
I
= I
* (e
BE
Q
C
S
= saturation current, q = electronic charge, V
S
, provided in the Diode Model Table
T
Table
) is 1.000. Given that most diodes are not perfect, the designers
trim
value that more closely matches the behavior of the diodes in
trim
T
= T
error(nf)
measured
is the offset in degrees C, T
is the diode ideality assumed by the temperature
trim
Min
Typ
Max
5
5
0.997
1.001
1.005
0.3
0.760
2.79
4.52
6.24
–1)
BE
24. In most sensing devices, an expected value
* (1 - n
/n
)
actual
trim
is in Kelvin, n
measured
Unit
Notes
200
μA
1,2
200
μA
1
3,4,5
3,4
Ω
3,6
= voltage across the transistor
(Table
24) can be used for
, each
trim
is the measured
actual
and the
trim
83
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