Datasheet

Datasheet 63
Thermal Specifications
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 core
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#.
As an output, PROCHOT# (Processor Hot) will go active when the processor
temperature monitoring sensor detects that the core has reached its maximum safe
operating temperature. This indicates that the processor Thermal Control Circuit (TCC)
has been activated, if enabled. As an input, assertion of PROCHOT# by the system will
activate the TCC, if enabled. The TCC will remain active until the system de-asserts
PROCHOT#.
PROCHOT# allows for some protection of 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.
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 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 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 Voltage Regulator-Down (VRD) 11 Design
Guide For Desktop and Transportable LGA775 Socket for details on implementing the
bi-directional PROCHOT# feature.
5.2.4 THERMTRIP# Signal
Regardless of whether or not Thermal Monitor 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 19). At this
point, the FSB signal THERMTRIP# will go active and stay active as described in
Table 19. 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 11.
5.3 Processor Thermal Features
The Celeron processor incorporates three methods of monitoring die temperature:
•Intel
®
Thermal Monitor
• Digital Thermal Sensor
The Intel Thermal Monitor (detailed in Section 5.4) must be used to determine when
the maximum specified processor junction temperature has been reached.