Intel Pentium 4 Processor with 512-KB L2 Cache on 0.13 Micron Process Thermal Design Guidelines

Thermal Specifications
R
38 Intel
®
Pentium
®
4 Processor Thermal Design Guide
3.4.7.1 Thermal Diode
The Pentium 4 processor with 512-KB L2 cache on 0.13 micron process incorporates an on-die
thermal diode, which can be used with an external device (thermal diode sensor) to monitor long-
term temperature trends. By averaging this data over long time periods (hours/days vs. min/sec), it
may be possible to derive a trend of the processor temperature. Analysis of this information could
be useful in detecting changes in the system environment that may require attention. Design
characteristics and usage models of the thermal diode sensors are described in datasheets available
from the thermal diode sensor manufacturers.
The processor thermal diode should not be relied upon to turn on fans, warn of processor cooling
system failure, or predict the onset of the thermal control circuit. As mentioned earlier, the
processor high thermal ramp rates make this unfeasible. An illustration of this is as follows. Many
thermal diode sensors report temperatures a maximum of 8 times per second. Within the 1/8
th
(0.125 s) second time period, the temperature is averaged over 1/16
th
of a second. In a scenario
where the silicon temperature ramps at 50 °C/s, or approximately 6°C/0.125 s, the processor will
be ~4.5 °C above the temperature reported by the thermal sensor. (Change in diode temperature
averaged over 1/16
th
seconds = ~1.5°C; temperature reported 1/16
th
second later at 1/8
th
second
when the actual processor temperature would be 6°C higher, see Figure 18).
Figure 18. Thermal Diode Sensor Time Delay
Processor Temperature
Time in 1/16
th
second intervals
Temperature is averaged
over 1/16
th
second
Temperature is
reported 1/16
th
second later
Processor
temperature
ramp
Processor Temperature
Time in 1/16
th
second intervals
Temperature is averaged
over 1/16
th
second
Temperature is
reported 1/16
th
second later
Processor
temperature
ramp