mpc8245ec Freescale Semiconductor, Inc, mpc8245ec Datasheet - Page 54

• Manufacturer Part Number: mpc8245ec
• Description: Mpc8245 Integrated Host Processor
• Manufacturer: Freescale Semiconductor, Inc

System Design
7.8.3
An estimation of the chip junction temperature, T
where
The junction-to-ambient thermal resistance is an industry-standard value that provides a quick and easy
estimation of thermal performance. Unfortunately, two values are in common usage: the value determined
on a single-layer board and the value obtained on a board with two planes. Which value is closer to the
application depends on the power dissipated by other components on the board. The value obtained on a
single-layer board is appropriate for the tightly packed printed-circuit board. The value obtained on the
board with the internal planes is usually appropriate if the board has low power dissipation and the
components are well separated.
When a heat sink is used, the thermal resistance is expressed as the sum of a junction-to-case thermal
resistance and a case-to-ambient thermal resistance:
where
54
Dow-Corning Corporation
Dow-Corning Electronic Materials
2200 W. Salzburg Rd.
Midland, MI 48686-0997
Internet: www.dow.com
Shin-Etsu MicroSi, Inc.
10028 S. 51st St.
Phoenix, AZ 85044
Internet: www.microsi.com
The Bergquist Company
18930 West 78
Chanhassen, MN 55317
Internet: www.bergquistcompany.com
Thermagon Inc.
4707 Detroit Ave.
Cleveland, OH 44102
Internet: www.thermagon.com
T
T
R
P
R
R
R
R
Heat Sink Usage
A
D
J
θJA
θJA
θJA
θJC
θCA
= T
= ambient temperature for the package (°C)
= power dissipation in the package (W)
= junction-to-case thermal resistance (°C/W)
= junction-to-ambient thermal resistance (°C/W)
= junction-to-ambient thermal resistance (°C/W)
= R
= case-to-ambient thermal resistance (°C/W)
A
+ (R
θJC
th
MPC8245 Integrated Processor Hardware Specifications, Rev. 10
θJA
+ R
St.
× P
θCA
D
)
J
, can be obtained from the equation:
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