Intel 640 User Guide - Page 36

Thermal Management Logic and Thermal Monitor Feature

R

36

Thermal/Mechanical Design Guide

4.2.7.2

Correction Factors for the On-Die Thermal Diode

A number of issues can affect the accuracy of the temperature reported by thermal diode sensors.

These include the diode ideality and the series resistance that are characteristics of the processor

on-die thermal diode. The processor datasheet provides the specification for these parameters. The

trace layout recommendations between the thermal diode sensors and the processor socket should

be followed as listed in the vendor datasheets. The design characteristics and usage models of the

thermal diode sensors should be reviewed in the datasheets available from the manufacturers.

The choice of a remote diode sensor measurement component has a significant impact to the

accuracy of the reported on-die diode temperature. The component vendors offer components that

have stated accuracy of ± 3° C to ± 1°C. The improved accuracy generally comes from the

number of times a current is passed through the diode and the ratios of the currents. Consult the

vendor datasheet for details on their measurement process and stated accuracy.

The ideality factor, n, represents the deviation from ideal diode behavior as exemplified by the

diode equation:

I

FW

= I

S

* (E

qVD/nkT

–1)

Where

I

FW

= forward bias current,

I

S

= saturation current,

q

= electronic charge,

V

= voltage across

the diode,

k

= Boltzmann Constant and

T

= absolute temperature (Kelvin). This equation

determines the ideality factor of an individual diode.

For the purpose of determining a correction factor to use with the thermal sensor, the ideality

equation can be simplified to the following:

T

ERROR

= T

MEASURED

* (1 – N

ACTUAL

/ N

TRIM

)

Where T

ERROR

= correction factor to add to the reported temperature, T

MEASURED

= temperature

reported by the thermal sensor (Kelvin), N

ACTUAL

= the ideality of the on-die thermal diode, N

TRIM

= the assumed ideality used by the thermal sensor. For the range of temperatures where the

thermal diode is being measured, 30–80 °C this error term is nearly constant.

The value of N

TRIM

is available from the datasheet of the device measuring the processor on die

thermal diode. N

ACTUAL

can be assumed to be typical for this equation.

The series resistance, R

T

, is provided to allow for a more accurate measurement of the on-die

thermal diode temperature. R

T

, as defined, includes the pads 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 * I

N

ln N

)

Where

T

ERROR

= sensor temperature error,

N =

sensor current ratio,

k

= Boltzmann Constant,

q

= electronic charge.

Section	Page
Contents	3
Figures	6
Tables	7
Revision History	8
1 Introduction	9
1.1 Document Goals and Scope	9
1.1.1 Importance of Thermal Management	9
1.1.2 Document Goals	9
1.1.3 Document Scope	10
1.2 References	11
1.3 Definition of Terms	12
2 Processor Thermal/Mechanical Information	15
2.1 Mechanical Requirements	15
2.1.1 Processor Package	15
2.1.2 Heatsink Attach	17
2.1.2.1 General Guidelines	17
2.1.2.2 Heatsink Clip Load Requirement	17
2.1.2.3 Additional Guidelines	18
2.2 Thermal Requirements	18
2.2.1 Processor Case Temperature	18
2.2.2 Thermal Profile	19
2.2.3 TCONTROL	20
2.3 Heatsink Design Considerations	21
2.3.1 Heatsink Size	22
2.3.2 Heatsink Mass	22
2.3.3 Package IHS Flatness	22
2.3.4 Thermal Interface Material	23
2.4 System Thermal Solution Considerations	23
2.4.1 Chassis Thermal Design Capabilities	23
2.4.2 Improving Chassis Thermal Performance	23
2.4.3 Summary	24
2.5 System Integration Considerations	24
3 Thermal Metrology	25
3.1 Characterizing Cooling Performance Requirements	25
3.1.1 Example	26
3.2 Processor Thermal Solution Performance Assessment	27
3.3 Local Ambient Temperature Measurement Guidelines	27
3.4 Processor Case Temperature Measurement Guidelines	30
4 Thermal Management Logic and Thermal Monitor Feature	31
4.1 Processor Power Dissipation	31
4.2 Thermal Monitor Implementation	31
4.2.1 PROCHOT# Signal	32
4.2.2 Thermal Control Circuit	32
4.2.3 Operation and Configuration	33
4.2.4 On-Demand Mode	34
4.2.5 System Considerations	34
4.2.6 Operating System and Application Software Considerations	35
4.2.7 On-Die Thermal Diode	35
4.2.7.1 Reading the On-Die Thermal Diode Interface	35
4.2.7.2 Correction Factors for the On-Die Thermal Diode	36
4.2.8 THERMTRIP# Signal	37
4.2.8.1 Cooling System Failure Warning	37
5 Intel® Thermal/Mechanical Reference Design Information	39
5.1 Intel Validation Criteria for the Reference Design	39
5.1.1 Heatsink Performance Target	39
5.1.2 Acoustics	40
5.1.3 Altitude	40
5.1.4 Reference Heatsink Thermal Validation	41
5.1.5 Fan Performance for Active Heatsink Thermal Solution	41
5.2 Environmental Reliability Testing	42
5.2.1 Structural Reliability Testing	42
5.2.1.1 Random Vibration Test Procedure	42
5.2.1.2 Shock Test Procedure	42
5.2.2 Power Cycling	44
5.2.3 Recommended BIOS/Processor/Memory Test Procedures	44
5.3 Material and Recycling Requirements	44
5.4 Safety Requirements	45
5.5 Geometric Envelope for ATX Intel® Reference Thermal Mechanical Design	45
5.6 ATX Reference Thermal Mechanical Solution for the Intel® Pentium® 4 Processor in the 775–Land LGA Package	46
5.7 Reference Attach Mechanism	48
5.7.1 Structural Design Strategy	48
5.7.2 Mechanical Interface to the Reference Attach Mechanism	49
6 Acoustic Fan Speed Control	53
6.1 Acoustic Fan Speed Control	53
6.2 Thermal Solution Design	53
6.2.1 Compliance to Thermal Profile	53
6.2.2 Determine Thermistor Set Points	53
6.2.3 Minimum Fan Speed Set Point	54
6.3 Board and System Implementation	55
6.3.1 Choosing Fan Speed Control Settings	55
6.3.1.1 Temperature to begin Fan Acceleration	56
6.3.1.2 Minimum PWM Duty Cycle	58
6.4 Combining Thermistor and Thermal Diode Control	59

Intel 640 User Guide - Page 36

Correction Factors for the On-Die Thermal Diode - review

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