Intel Xeon Processor with 800 MHz System Bus Thermal/Mechanical Design Guide

Intel® Xeon™ Processor with 800 MHz System Bus Thermal/Mechanical Design Guidelines 73
Processor Thermal Management Logic
and Thermal Monitor Features F
F.1 Thermal Management Logic and Thermal Monitor
Feature
F.1.1 Processor Power Dissipation
An increase in processor operating frequency not only increases system performance, but also
increases the processor power dissipation. The relationship between frequency and power is
generalized in the following equation: P = CV
2
F (where P = power, C = capacitance, V = voltage,
F = frequency). From this equation, it is evident that power increases linearly with frequency and
with the square of voltage. In the absence of power saving technologies, ever increasing
frequencies will result in processors with power dissipations in the hundreds of watts. Fortunately,
there are numerous ways to reduce the power consumption of a processor, and Intel is aggressively
pursuing low power design techniques. For example, decreasing the operating voltage, reducing
unnecessary transistor activity, and using more power efficient circuits can significantly reduce
processor power consumption.
An on-die thermal management feature called Thermal Monitor is available on the Intel Xeon
Processor with 800 MHz System Bus. It provides a thermal management approach to support the
continued increases in processor frequency and performance. By using a highly accurate on-die
temperature sensing circuit and a fast acting temperature control circuit, the processor can rapidly
initiate thermal management control. The Thermal Monitor can reduce cooling solution cost, by
allowing designs to target TDP instead of maximum processor power.
F.1.2 Thermal Monitor Implementation
On the Intel Xeon Processor with 800 MHz System Bus, the Thermal Monitor is integrated into the
processor silicon. The Thermal Monitor includes:
• An on-die temperature sensing circuit.
• An external output signal (PROCHOT#) that indicates the processor has reached its maximum
operating temperature.
• An external input signal (FORCEPR#) that allows the platform to force a power reduction by
the processor by activating the TCC.
• A TCC that can reduce processor temperature by rapidly reducing power consumption when
the on-die temperature sensor indicates that it has reached the maximum operating point.
• Registers to determine the processor thermal status.
The processor temperature is determined through an analog thermal sensor circuit comprised of a
temperature sensing diode, a factory calibrated reference current source, and a current comparator
(see Figure F-27). A voltage applied across the diode induces a current flow that varies with
temperature. By comparing this current with the reference current, the processor temperature can