MPC8358 FREESCALE [Freescale Semiconductor, Inc], MPC8358 Datasheet - Page 87

• Manufacturer Part Number: MPC8358
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

many natural convection and especially closed box applications, the board temperature at the perimeter
(edge) of the package will be approximately the same as the local air temperature near the device.
Specifying the local ambient conditions explicitly as the board temperature provides a more precise
description of the local ambient conditions that determine the temperature of the device. At a known board
temperature, the junction temperature is estimated using the following equation:
When the heat loss from the package case to the air can be ignored, acceptable predictions of junction
temperature can be made. The application board should be similar to the thermal test condition: the
component is soldered to a board with internal planes.
23.2.3
To determine the junction temperature of the device in the application after prototypes are available, the
Thermal Characterization Parameter (Ψ
measurement of the temperature at the top center of the package case using the following equation:
The thermal characterization parameter is measured per JESD51-2 specification using a 40 gauge type T
thermocouple epoxied to the top center of the package case. The thermocouple should be positioned so
that the thermocouple junction rests on the package. A small amount of epoxy is placed over the
thermocouple junction and over about 1 mm of wire extending from the junction. The thermocouple wire
is placed flat against the package case to avoid measurement errors caused by cooling effects of the
thermocouple wire.
23.2.4
In some application environments, a heat sink will be required to provide the necessary thermal
management of the device. 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:
Freescale Semiconductor
MPC8358E PowerQUICC™ II Pro Processor Revision 2.1 PBGA Silicon Hardware Specifications, Rev. 1
Experimental Determination of Junction Temperature
Heat Sinks and Junction-to-Case Thermal Resistance
T
where:
T
T
R
P
T
where:
T
T
Ψ
P
R
where:
J
J
B
J
J
T
θ
D
D
θ
JT
JA
JA
= T
= junction temperature (°C)
= T
= junction temperature (°C)
= thermocouple temperature on top of package (°C)
= board temperature at the package perimeter (°C)
= power dissipation in the package (W)
= power dissipation in the package (W)
= junction to ambient thermal resistance (°C/W)
= junction to board thermal resistance (°C/W) per JESD51-8
= R
B
T
+ (
+ (R
θ
JC
Ψ
θ
JT
+ R
JB
× P
JT
× P
θ
CA
) can be used to determine the junction temperature with a
D
D
)
)
Thermal
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