參數(shù)資料
型號: MPC7450RX667LX
廠商: MOTOROLA INC
元件分類: 微控制器/微處理器
英文描述: 32-BIT, 667 MHz, RISC PROCESSOR, CBGA483
封裝: 29 X 29 MM, 3.22 MM HEIGHT, 1.27 MM PITCH, CERAMIC, BGA-483
文件頁數(shù): 53/60頁
文件大小: 1296K
代理商: MPC7450RX667LX
MPC7450 RISC Microprocessor Hardware Specifications
57
System Design Information
Loctite Corporation
860-571-5100
1001 Trout Brook Crossing
Rocky Hill, CT 06067-3910
Internet: www.loctite.com
The following section provides a heat sink selection example using one of the commercially available heat
sinks.
1.9.9.3 Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature can be expressed as follows:
Tj = Ta + Tr + (θjc + θint + θsa) × Pd
where:
Tj is the die-junction temperature
Ta is the inlet cabinet ambient temperature
Tr is the air temperature rise within the computer cabinet
θ
jc is the junction-to-case thermal resistance
θ
int is the adhesive or interface material thermal resistance
θ
sa is the heat sink base-to-ambient thermal resistance
Pd is the power dissipated by the device
During operation, the die-junction temperatures (Tj) should be maintained less than the value specified in
Table 4. The temperature of the air cooling the component greatly depends upon the ambient inlet air
temperature and the air temperature rise within the electronic cabinet. An electronic cabinet inlet-air
temperature (Ta) may range from 30° to 40°C. The air temperature rise within a cabinet (Tr) may be in the
range of 5° to 10°C. The thermal resistance of the thermal interface material (
θ
int) is typically about
1.5°C/W. Assuming a Ta of 30°C, a Tr of 5°C, a CBGA package θjc = 0.1, and a power consumption (Pd) of
19 W, the following expression for Tj is obtained:
Die-junction temperature:
Tj = 30°C + 5°C + (0.1°C/W + 1.5°C/W + θsa) × 19 W
For this example, a
θ
sa value of 2.08°C/W or less is required to maintain the die junction temperature below
the maximum value of Table 4.
Though the die junction-to-ambient and the heat sink-to-ambient thermal resistances are a common
figure-of-merit used for comparing the thermal performance of various microelectronic packaging
technologies, one should exercise caution when only using this metric in determining thermal management
because no single parameter can adequately describe three-dimensional heat flow. The final die-junction
operating temperature is not only a function of the component-level thermal resistance, but the system-level
design and its operating conditions. In addition to the component's power consumption, a number of factors
affect the final operating die-junction temperature—airflow, board population (local heat flux of adjacent
components), heat sink efficiency, heat sink attach, heat sink placement, next-level interconnect technology,
system air temperature rise, altitude, etc.
Due to the complexity and the many variations of system-level boundary conditions for today's
microelectronic equipment, the combined effects of the heat transfer mechanisms (radiation, convection,
and conduction) may vary widely. For these reasons, we recommend using conjugate heat transfer models
for the board, as well as system-level designs.
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