Datasheet

Datasheet 89
Thermal Specifications and Design Considerations
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.
NOTES:
1. Intel does not support or recommend operation of the thermal diode under reverse bias.
2. Same as I
FW
in Table 29
3. Characterizedacross a range of 50 – 80 °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:
I
C
= I
S
* (e
qV
BE
/n
Q
kT
–1)
Where I
S
= saturation current, q = electronic charge, V
BE
= voltage across the transistor base emitter
junction (same nodes as VD), k = Boltzmann Constant, and T = absolute temperature (Kelvin).
6. The series resistance, R
T,
provided in the Diode Model Table (Table 29) can be used for
more accurate readings as needed.
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 29. 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.
To improve the accuracy of diode based temperature measurements, a new register
containing Thermal Diode Offset data has been added to the processor. During
manufacturing each processor 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
Table 30. Thermal “Diode” Parameters using Transistor Model
Symbol Parameter Min Typ Max Unit Notes
I
FW
Forward Bias Current 5 - 200 µA 1, 2
I
E
Emitter Current 5 200
n
Q
Transistor Ideality 0.997 1.001 1.005 - 3, 4, 5
Beta 0.391 0.760 3, 4
R
T
Series Resistance 2.79 4.52 6.24 Ω 3, 6