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Thermal Specifications and Design Considerations

5.1.2

Thermal Metrology

The maximum and minimum case temperatures (TC) are specified in Table 5-1. These temperature

specifications are meant to help ensure proper operation of the processor. Figure 5-3 illustrates

where Intel recommends TC thermal measurements should be made. For detailed guidelines on

temperature measurement methodology, refer to the Intel® Pentium® 4 Processor on 90 nm

Process in the 775-Land Package Thermal Design Guidelines.

5.2

Processor Thermal Features

5.2.1

Thermal Monitor

The Thermal Monitor feature helps control the processor temperature by activating the TCC when

the processor silicon reaches its maximum operating temperature. The TCC reduces processor

power consumption as needed by modulating (starting and stopping) the internal processor core

clocks. The Thermal Monitor feature must be enabled for the processor to be operating

within specifications. The temperature at which Thermal Monitor activates the thermal control

circuit is not user configurable and is not software visible. Bus traffic is snooped in the normal

manner, and interrupt requests are latched (and serviced during the time that the clocks are on)

while the TCC is active.

When the Thermal Monitor feature is enabled, and a high temperature situation exists (i.e., TCC is

active), the clocks will be modulated by alternately turning the clocks off and on at a duty cycle

specific to the processor (typically 30–50%). Clocks often will not be off for more than

3.0 microseconds when the TCC is active. Cycle times are processor speed dependent and will

decrease as processor core frequencies increase. A small amount of hysteresis has been included to

prevent rapid active/inactive transitions of the TCC when the processor temperature is near its

maximum operating temperature. Once the temperature has dropped below the maximum

operating temperature, and the hysteresis timer has expired, the TCC goes inactive and clock

modulation ceases.

Figure 5-3. Case Temperature (TC) Measurement Location

37.5 mm

Measure T

C at this po int

(geometric center of the package)

37.5 mm

Measure T

C at this po int

(geometric center of the package)

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