Thermal Characteristics
4
MPC8280, MPC8275VR, MPC8275ZQ only.
4
Thermal Characteristics
This table describes thermal characteristics. See
for information on a given SoC’s package.
Discussions of each characteristic are provided in
through
For the these discussions, P
D
= (V
DD
×
I
DD
) +
PI/O, where PI/O is the power dissipation of the I/O drivers.
Table 7. Thermal Characteristics
Characteristic
Junction-to-ambient—
single-layer board
1
Junction-to-ambient—
four-layer board
Junction-to-board
2
Junction-to-case
3
Junction-to-package top
4
1
2
Symbol
Value
27
Unit
°C/W
Air Flow
Natural convection
1 m/s
Natural convection
R
θJA
21
19
R
θJA
R
θJB
R
θJC
R
θJT
16
11
8
2
°C/W
°C/W
°C/W
°C/W
1 m/s
—
—
—
Assumes no thermal vias
Thermal resistance between the die and the printed circuit board per JEDEC JESD51-8. Board temperature is
measured on the top surface of the board near the package.
3
Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL SPEC-883
Method 1012.1).
4
Thermal characterization parameter indicating the temperature difference between package top and the junction
temperature per JEDEC JESD51-2. When Greek letters are not available, the thermal characterization parameter is
written as Psi-JT.
4.1
Estimation with Junction-to-Ambient Thermal Resistance
C can be obtained from the following equation:
An estimation of the chip junction temperature, T
J
, in
T
J
= T
A
+ (R
θJA
×
P
D
)
where:
T
A
= ambient temperature (ºC)
R
θJA
= package junction-to-ambient thermal resistance (ºC/W)
P
D
= power dissipation in package
The junction-to-ambient thermal resistance is an industry standard value that provides a quick and easy
estimation of thermal performance. However, the answer is only an estimate; test cases have demonstrated
that errors of a factor of two (in the quantity T
J
–
T
A
) are possible.
MPC8272 PowerQUICC II Family Hardware Specifications, Rev. 3
14
Freescale Semiconductor
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
