AMD 8 manual Temperature Offset Correction, Preliminary Information

Preliminary Information

AMD Athlon™ XP Processor Model 8 Data Sheet 25175H— March 2003

Equation (1) shows the ideal diode calculation.

VBE =	k	⋅ T ⋅ ln	 IC	(1)
	nf, lumped ⋅ --		---
	q		 IS

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) is the formula for calculating the temperature of a thermal diode.

TVBE, high – VBE, low

=--------------------------------------------------------------

k	⋅ ln	 Ihigh	(2)
nf, lumped ⋅ --		-------
q		 Ilow 

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 30 shows the constants and variables used to calculate the temperature offset correction.

Table 30. Constants and Variables Used in Temperature Offset Equations

Equation Symbol	Variable, Constant Description
nf, actual	Actual ideality factor
nf, lumped	Lumped ideality factor
nf, TS	Ideality factor assumed by temperature sensor
Ihigh	High sourcing current
Ilow	Low sourcing current
Tdie, spec	Die temperature specification
Toffset	Temperature offset

84 Appendix A - Thermal Diode Calculations