Intel PentiumD 950 HH80553PG0964M User Manual

89

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 

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 (

) 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 

. 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 

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