Intel Pentium 4 Processor on 90 nm Process Thermal and Mechanical Design Guidelines

Thermal Requirements

Intel

Pentium

4 on 90 nm Process Thermal Design Guide 25

be determined. The reference current source corresponds to the diode current when at the

maximum permissible processor operating temperature.

The temperature at which PROCHOT# goes active is individually calibrated during

manufacturing. The power dissipation of each processor affects the set point temperature. The

temperature where PROCHOT# goes active is roughly parallel to the thermal profile. Once

configured, the processor temperature at which the PROCHOT# signal is asserted is not re-

configurable.

Note: A thermal solution designed to meet the thermal profile and TDP targets should rarely experience

activation of the TCC.

Figure 6. Thermal Sensor Circuit

PROCHOT#

Temperature sensing diode

Reference current source

Current comparator

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 de-asserted. 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 thermal control

circuit activates is set to the same temperature at which the processor is tested and at which

PROCHOT# asserts.

3.4.2.1 Thermal Monitor

The thermal control circuit 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.

Figure 7 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 and control the Thermal Monitor behavior.