Thermal Control Circuit; Concept For Clocks Under Thermal Monitor Control - Intel Celeron D Thermal Design Manual

Thermal Management Logic and Thermal Monitor
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), which activates 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 PROCHOT# signal is available internally to the processor as well as externally. External
indication of the processor temperature status is provided through the bus signal PROCHOT#.
When the processor temperature reaches the trip point, PROCHOT# is asserted. When the
processor temperature is below the trip point, PROCHOT# is deasserted. Assertion of the
PROCHOT# signal is independent of any register settings within the processor. It is asserted any
time the processor die temperature reaches the trip point. The point where the TCC activates is set
to the same temperature at which PROCHOT# asserts.
4.2.2

Thermal Control Circuit

The TCC portion of the Thermal Monitor must be enabled for the processor to operate within
specifications. The Thermal Monitor's TCC, when active, lowers the processor temperature by
reducing the power consumed by the processor. In the original implementation of thermal monitor
this is done by changing the duty cycle of the internal processor clocks, resulting in a lower
effective frequency. When active, the TCC turns the processor clocks off and then back on with a
predetermined duty cycle. The duty cycle is processor specific, and is fixed for a particular
processor. The maximum time period the clocks are disabled is ~3 μs, and is frequency dependent.
Higher frequency processors will disable the internal clocks for a shorter time period.
illustrates the relationship between the internal processor clocks and PROCHOT#.
Performance counter registers, status bits in model specific registers (MSRs), and the PROCHOT#
output pin are available to monitor the Thermal Monitor behavior.
Figure 7. Concept for Clocks under Thermal Monitor Control
PROCHOT#
Normal clock
Internal clock
Duty cycle control
Resultant
internal clock
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Celeron D Processor in the 775-Land LGA Package Thermal Design Guide
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