SPC5561MZQ132 Freescale Semiconductor / Motorola, SPC5561MZQ132 Datasheet - Page 7

• Manufacturer Part Number: SPC5561MZQ132
• Description: Power Architecture TM 32-bit MCU for Automotive
• Manufacturer: Freescale Semiconductor / Motorola

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 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:
R
change the case-to-ambient thermal resistance, R
add a heat sink, change the 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
temperature at the top center of the package case using the following equation:
The thermal characterization parameter is measured in compliance with the JESD51-2 specification using
a 40-gauge type T thermocouple epoxied to the top center of the package case. Position the thermocouple
Freescale Semiconductor
θJC
is device related and is not affected by other factors. The thermal environment can be controlled to
where:
where:
where:
T
T
T
R
P
R
R
R
R
T
T
Ψ
P
D
D
J
J
B
J
T
θJB
θJA
θJA
θJC
θCA
JT
= T
= junction temperature (
= T
= board temperature at the package perimeter (
= power dissipation in the package (W)
= thermocouple temperature on top of the package (
= power dissipation in the package (W)
= thermal characterization parameter (
= 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
MPC5561 Microcontroller Data Sheet, Rev. 2.0
D
D
)
)
JT
) to determine the junction temperature by measuring the
o
C)
θCA
. For example, change the air flow around the device,
o
o
C/W)
o
C/W)
o
C/W)
C/W) per JESD51-8
o
C/W)
o
C/W)
o
C)
Electrical Characteristics
7