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10.3 Thermal Assist Unit
With the increasing power dissipation of high-perfonnance processors and operating
conditions that span a wider range of temperatures than desktop systems, thermal
management becomes an essential part of system design to ensure reliable operation of
portable systems. One key aspect of thennal management is ensuring that the junction
temperature of the microprocessor does not exceed the operating specification. While the
case temperature can be measured with an external thermal sensor, the thennal constant
from the junction to the case can be large, and accuracy can be a problem. This may lead to
lower overall system perfonnance due to the necessary compensation to alleviate
measurement deficiencies.
The MPC750 provides the system designer an efficient means of monitoring junction
temperature through the incorporation of an on-chip thennal sensor and programmable
control logic to enable a thennal management implementation tightly coupled to the
processor for improved perfonnance and reliability.
10.3.1 Thermal Assist Unit Overview
The on-chip thennal assist unit (TAU) is composed of a thermal sensor, a digital-to-analog
converter (DAC), a comparator, control logic, and three dedicated SPRs. See Figure 10-1
for a block diagram of the TAU.
Thermal Interrupt
Request
(OxI700)
Figure 10-1. Thermal Assist Unit Block Diagram
The TAU provides thennal control by periodically comparing the MPC750's junction
temperature against user-programmed thresholds, and generating a thermal management
interrupt if the threshold values are crossed. The TAU also enables the user to determine the
. junction temperature through a software successive approximation routine.
10-6
MPC750 RISC Microprocessor User's Manual
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