mpc8241tzq266c Freescale Semiconductor, Inc, mpc8241tzq266c Datasheet - Page 51

• Manufacturer Part Number: mpc8241tzq266c
• Description: Mpc8241 Integrated Processor Hardware Specifications
• Manufacturer: Freescale Semiconductor, Inc

7.7.3
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. For packages such as the PBGA,
these values can be different by a factor of two. 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:
R
change the case-to-ambient thermal resistance, R
sink, the airflow around the device, the interface material, the mounting arrangement on the printed-circuit
board, or the thermal dissipation on the printed-circuit board surrounding the device.
To determine the junction temperature of the device in the application when heat sinks are not used, the
thermal characterization parameter (ψ
using the following equation:
Freescale Semiconductor
θJC
is device-related and cannot be influenced by the user. The user controls the thermal environment to
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T
R
P
R
R
R
A
D
θJA
θJA
θJC
θCA
= ambient temperature for the package (°C)
= power dissipation in the package (W)
Heat Sink Usage
= junction-to-case thermal resistance (°C/W)
= junction-to-ambient thermal resistance (°C/W)
= junction-to-ambient thermal resistance (°C/W)
= case-to-ambient thermal resistance (°C/W)
T
R
T
J
θJA
J
= T
= T
= R
A
T
+ (ψ
+ (R
θJC
MPC8241 Integrated Processor Hardware Specifications, Rev. 10
JT
θJA
+ R
× P
× P
θCA
D
D
)
)
JT
) measures the temperature at the top center of the package case
θCA
J
, can be obtained from the equation:
. For instance, the user can change the size of the heat
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System Design Information
51