MPC857DSL Motorola, MPC857DSL Datasheet - Page 14

• Manufacturer Part Number: MPC857DSL
• Description: (MPC857 / MPC862) Hardware Specifications
• Manufacturer: Motorola

Thermal Calculation and Measurement
Thermal Calculation and Measurement
If the board temperature is known, an estimate of the junction temperature in the environment can be made
using the following equation:
where:
If the board temperature is known and the heat loss from the package case to the air can be ignored,
acceptable predictions of junction temperature can be made. For this method to work, the board and board
mounting must be similar to the test board used to determine the junction-to-board thermal resistance,
namely a 2s2p (board with a power and a ground plane) and vias attaching the thermal balls to the ground
plane.
7.4
When the board temperature is not known, a thermal simulation of the application is needed. The simple
two resistor model can be used with the thermal simulation of the application [2], or a more accurate and
complex model of the package can be used in the thermal simulation.
7.5
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:
where:
The thermal characterization parameter is measured per JESD51-2 specification published by JEDEC 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.
7.6
Semiconductor Equipment and Materials International
805 East Middlefield Rd.
Mountain View, CA 94043
MIL-SPEC and EIA/JESD (JEDEC) Specifications
(Available from Global Engineering Documents)
JEDEC Specifications
14
T
T
J
J
= T
= T
R
T
P
Estimation Using Simulation
Experimental Determination
Ψ
T
P
References
D
D
B
T
θJB
JT
B
T
= thermocouple temperature on top of package
= board temperature (ºC)
= power dissipation in package
= power dissipation in package
+(Ψ
+(R
= thermal characterization parameter
= junction-to-board thermal resistance (ºC/W)
θJB
JT
x P
x P
D
D
MPC862/857T/857DSL Hardware Specifications
Freescale Semiconductor, Inc.
)
)
For More Information On This Product,
Go to: www.freescale.com
JT
) can be used to determine the junction temperature with a
[phone]
800-854-7179 or
303-397-7956
http://www.jedec.org
MOTOROLA