mpc5645s Freescale Semiconductor, Inc, mpc5645s Datasheet - Page 70

• Manufacturer Part Number: mpc5645s
• Description: Mpc5645s Microcontroller Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

Electrical characteristics
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 (
the following equation:
where:
T

P
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 so that the thermocouple junction rests
on the package. Place a small amount of epoxy on the thermocouple junction and approximately 1 mm of wire extending from
the junction. Place the thermocouple wire flat against the package case to avoid measurement errors caused by the cooling
effects of the thermocouple wire.
References:
Semiconductor Equipment and Materials International
805 East Middlefield Rd.
Mountain View, CA 94043
[phone]
MIL-SPEC and EIA/JESD (JEDEC) specifications are available from Global Engineering Documents at 800-854-7179 or
303-397-7956.
JEDEC specifications are available on the WEB at http://www.jedec.org.
70
D
T
JT
= thermocouple temperature on top of the package (
= power dissipation in the package (W)
= thermal characterization parameter (
JT
) to determine the junction temperature by measuring the temperature at the top center of the package case using
MPC5645S Microcontroller Data Sheet, Rev. 6
o
C/W)
T
J
= T
T
o
C)
+ (
JT
x P
D
)
Freescale Semiconductor
Eqn. 4