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Thermal Specifications and Design Considerations

increments. On-Demand mode may be used in conjunction with the Thermal Monitor. If the system

tries to enable On-Demand mode at the same time the TCC is engaged, the factory configured duty

cycle of the TCC will override the duty cycle selected by the On-Demand mode.

5.2.3

PROCHOT# Signal Pin

An external signal, PROCHOT# (processor hot), is asserted when the processor die temperature

has reached its maximum operating temperature. If the Thermal Monitor is enabled (note that the

Thermal Monitor must be enabled for the processor to be operating within specification), the TCC

will be active when PROCHOT# is asserted. The processor can be configured to generate an

interrupt upon the assertion or de-assertion of PROCHOT#. Refer to the Intel Architecture

Software Developer's Manuals for specific register and programming details.

The Celeron D processor implements a bi-directional PROCHOT# capability to allow system

designs to protect various components from over-temperature situations. The PROCHOT# signal is

bi-directional in that it can either signal when the processor has reached its maximum operating

temperature or be driven from an external source to activate the TCC. The ability to activate the

TCC via PROCHOT# can provide a means for thermal protection of system components.

One application is the thermal protection of voltage regulators (VR). System designers can create a

circuit to monitor the VR temperature and activate the TCC when the temperature limit of the VR

is reached. By asserting PROCHOT# (pulled-low) and activating the TCC, the VR can cool down

as a result of reduced processor power consumption. Bi-directional PROCHOT# can allow VR

thermal designs to target maximum sustained current instead of maximum current. Systems should

still provide proper cooling for the VR, and rely on bi-directional PROCHOT# only as a backup in

case of system cooling failure. The system thermal design should allow the power delivery

circuitry to operate within its temperature specification even while the processor is operating at its

Thermal Design Power. With a properly designed and characterized thermal solution, it is

anticipated that bi-directional PROCHOT# would only be asserted for very short periods of time

when running the most power intensive applications. An under-designed thermal solution that is

not able to prevent excessive assertion of PROCHOT# in the anticipated ambient environment may

cause a noticeable performance loss. Refer to the applicable chipset platform design guide and the

applicable VRD design guide for details on implementing the bi-directional PROCHOT# feature.

5.2.4

THERMTRIP# Signal Pin

Regardless of whether or not the Thermal Monitor feature is enabled, in the event of a catastrophic

cooling failure, the processor will automatically shut down when the silicon has reached an

elevated temperature (refer to the THERMTRIP# definition in Table 4-3). At this point, the FSB

signal THERMTRIP# will go active and stay active as described in Table 4-3. THERMTRIP#

activation is independent of processor activity and does not generate any bus cycles.

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