Thermal Specifications and Design Considerations
however, 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.
5.2.4
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 one or both cores 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, for both cores. 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 (either core) 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) 11.0
Processor Power Delivery Design Guidelines For Desktop LGA775 Socket for details on
implementing the bi-directional PROCHOT# feature.
5.2.5
THERMTRIP# Signal
Regardless of whether or not Thermal Monitor or Thermal Monitor 2 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.
5.3
Thermal Diode
The processor incorporates an on-die PNP transistor where the base emitter junction is
used as a thermal "diode", with its collector shorted to ground. A thermal sensor
located on the system board may monitor the die temperature of the processor for
thermal management and fan speed control. Table 5-5,Table 5-6, and Table 7 provide
Dual-Core Intel® Xeon® Processor 3000 Series Datasheet
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