Intel Pentium 4 Processor Extreme Edition on 0.13 Micron Process in the 775-Land Package Datasheet

72 Datasheet
Thermal Specifications and Design Considerations
programmable via bits 3:1 of the same ACPI P_CNT Control Register. In On-Demand mode, the
duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/12.5% off in 12.5%
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
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 Pentium 4 processor Extreme Edition in the 775-land package 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 of PROCHOT# 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 he Voltage
Regulator-Down (VRD) 10.1 Design Guide for Desktop and Transportable Socket 775 for details
on implementing the bi-directional PROCHOT# feature. Contact your Intel representative for
further details and documentation.
5.2.4 THERMTRIP# Signal
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. If
THERMTRIP# is asserted, processor core voltage (V
CC
) must be removed within the timeframe
defined in Table 2-7.