mpc5632m Freescale Semiconductor, Inc, mpc5632m Datasheet - Page 56

• Manufacturer Part Number: mpc5632m
• Description: Mpc5634m Microcontroller Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

Electrical Characteristics
As a general rule, the value obtained on a single-layer board is within the normal range for the tightly packed printed circuit
board. The value obtained on a board with the internal planes is usually within the normal range if the application board has:
The thermal performance of any component depends on the power dissipation of the 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:
where:
When the heat loss from the package case to the air does not factor into the calculation, an acceptable value for the junction
temperature is predictable. Ensure the application board is similar to the thermal test condition, with the component soldered to
a board with internal planes.
The thermal resistance is expressed as the sum of a junction-to-case thermal resistance plus a case-to-ambient thermal
resistance:
where:
R
case-to-ambient thermal resistance, R
mounting arrangement on the 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 90% of the heat flow is through the case to 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 thermal resistance describes when using a heat sink 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 to generate simple
estimations and for computational fluid dynamics (CFD) thermal models.
To determine the junction temperature of the device in the application on a prototype board, use the thermal characterization
parameter (Ψ
the following equation:
where:
56
θJC
•
•
•
s device related and is not affected by other factors. The thermal environment can be controlled to change the
One oz. (35 micron nominal thickness) internal planes
Components are well separated
Overall power dissipation on the board is less than 0.02 W/cm2
T
R
P
R
R
R
T
D
B
T
θJB
θJA
θJC
θCA
= thermocouple temperature on top of the package (
= board temperature for the package perimeter (
= power dissipation in the package (W)
JT
= junction-to-board thermal resistance (
= junction-to-case thermal resistance (
= junction-to-ambient thermal resistance (
= case to ambient thermal resistance (
) to determine the junction temperature by measuring the temperature at the top center of the package case using
θCA
Preliminary—Subject to Change Without Notice
MPC5634M Microcontroller Data Sheet, Rev. 3
. For example, change the air flow around the device, add a heat sink, change the
T
T
R
J
J
θJA
= T
= T
o
o
C/W)
C/W)
o
= R
B
T
C/W) per JESD51-8S
+ (R
o
+ (Ψ
C/W)
θJC
o
θJB
C)
JT
+ R
o
x P
C)
* P
θCA
D
D
)
)
Freescale Semiconductor
Eqn. 2
Eqn. 3
Eqn. 4