641 datasheet(79/106 Pages) INTEL

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Thermal Specifications and Design Considerations

5.1.2

Thermal Metrology

The maximum and minimum case temperatures (TC) for the processor is specified in

Table 26. This temperature specification is meant to help ensure proper operation of

the processor. Figure 14 illustrates where Intel recommends TC thermal measurements

should be made. For detailed guidelines on temperature measurement methodology,

refer to the appropriate processor Thermal and Mechanical Design Guidelines (see

Section 1.2).

5.2

Processor Thermal Features

5.2.1

Thermal Monitor

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

thermal control circuit (TCC) when the processor silicon reaches its maximum operating

temperature. The TCC reduces processor power consumption 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 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 14.

Case Temperature (TC) Measurement Location

37.5 mm

Measure T

C a t this point

(geometric center of the package)

37.5 mm

Measure T

C a t this point

(geometric center of the package)

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