MPC8347 FREESCALE [Freescale Semiconductor, Inc], MPC8347 Datasheet - Page 94

• Manufacturer Part Number: MPC8347
• Description: Integrated Host Processor Hardware Specifications
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Thermal
many natural convection and especially closed box applications, the board temperature at the perimeter
(edge) of the package is 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.
20.2.3
To determine the junction temperature of the device in the application after prototypes are available, use
the thermal characterization parameter (
temperature at the top center of the package case using the following equation:
The thermal characterization parameter is measured per the 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.
94
Experimental Determination of Junction Temperature
MPC8347EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 3
T
where:
T
where:
J
J
= T
= T
T
R
P
T
T
Ψ
P
A
T
A
J
T
θ
D
D
JT
+ (R
+ (
JA
= junction temperature (°C)
= ambient temperature for the package (°C)
= thermocouple temperature on top of package (°C)
= power dissipation in the package (W)
= power dissipation in the package (W)
= junction to ambient thermal resistance (°C/W)
Ψ
= junction to ambient thermal resistance (°C/W)
θ
JT
JA
× P
× P
D
D
)
)
Ψ
JT
) to determine the junction temperature and a measure of the
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