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Appendix A - Thermal Diode Calculations
AMD Sempron™ Processor Model 10 with 256K L2 Cache Data Sheet
31994A —1 August  2004
 
Equation (1) shows the ideal diode calculation. 
Sourcing two currents and using Equation (1) derives the 
difference in the base-to-emitter voltage that leads to finding 
the diode temperature as shown in Equation (2). The use of 
dual sourcing currents allows the measurement of the thermal 
diode temperature to be more accurate and less susceptible to 
die and process revisions. Temperature sensors that utilize 
series resistance cancellation can use more than two sourcing 
currents and are suitable to be used with the AMD thermal 
diode.  Equation  ( 2 ) i s  t h e  for mu la  for  c a lcu la t ing  t h e  
temperature of a thermal diode.
Temperature Offset Correction
A temperature offset may be required to correct the value 
measured by a temperature sensor.  An offset is necessary if a 
difference exists between the lumped ideality factor of the 
processor and the ideality factor assumed by the temperature 
sensor. The lumped ideality factor can be calculated using the 
equations in this section to find the temperature offset that 
should be used with the temperature sensor.
Table 25 shows the constants and variables used to calculate the 
temperature offset correction.
(1)
V
BE
n
f lumped
,
k
q
--- T
I
C
I
S
----
⎝ ⎠
⎛ ⎞
ln
⋅ ⋅ ⋅
=
(2)
T
V
BE high
,
V
BE low
,
n
f lumped
,
k
q
---
I
high
I
low
--------
ln
⋅ ⋅
---------------------------------------------------------------
=
Table 25. Constants and Variables Used in Temperature Offset Equations
Equation Symbol
Variable, Constant Description
n
f, actual
Actual ideality factor
n
f, lumped
Lumped ideality factor
n
f, TS
Ideality factor assumed by temperature sensor
I
high
High sourcing current
I
low
Low sourcing current
T
die, spec
Die temperature specification
T
offset
Temperature offset