mpc5534mzq66 Freescale Semiconductor, Inc, mpc5534mzq66 Datasheet - Page 7

• Manufacturer Part Number: mpc5534mzq66
• Description: Mpc5534 High Performance Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

The thermal performance of any component depends strongly on the power dissipation of surrounding
components. In addition, the ambient temperature varies widely within the application. For 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, with the
component soldered to a board with internal planes.
Historically, the thermal resistance has frequently been expressed as the sum of a junction to case thermal
resistance and a case to ambient thermal resistance:
R
change the case to ambient thermal resistance, R
the device, add a heat sink, change the mounting arrangement on printed circuit board, or change the
thermal dissipation on the printed circuit board surrounding the device. This description is most useful for
packages with heat sinks where some 90% of the heat flow is through the case to the heat sink to ambient.
For most packages, a better model is required.
A more accurate two-resistor thermal model can be constructed from the junction to board thermal
resistance and the junction to case thermal resistance. The junction to case covers the situation where a
heat sink will be used or where a substantial amount of heat is dissipated from the top of the package. The
junction to board thermal resistance describes the thermal performance when most of the heat is conducted
to the printed circuit board. This model can be used for either hand estimations or for a computational fluid
dynamics (CFD) thermal model.
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:
Freescale Semiconductor
θJC
is device related and cannot be influenced by the user. The user controls the thermal environment to
where:
where:
T
T
T
R
P
R
R
R
R
T
D
J
J
B
J
θJB
θJA
θJA
θJC
θCA
= T
= junction temperature (
= T
= board temperature at the package perimeter (
= power dissipation in the package (W)
= junction to board thermal resistance (
= junction to case thermal resistance (
= R
= junction to ambient thermal resistance (
= case to ambient thermal resistance (
B
T
+ (R
+ (Ψ
θJC
θJB
+ R
JT
× P
× P
θCA
Preliminary—Subject to Change Without Notice
MPC5534 Microcontroller Data Sheet, Rev. 0
D
D
)
)
JT
o
) can be used to determine the junction temperature with a
C)
θCA
. For instance, the user can change the air flow around
o
o
C/W)
o
C/W)
C/W) per JESD51-8
o
C/W)
o
C/W)
Electrical Characteristics
7