MPC8280 PowerQUICC II Family Hardware Specifications, Rev. 2
12
Freescale Semiconductor
Thermal Characteristics
4
Thermal Characteristics
This table describes thermal characteristics for both the packages. See
Table 2 for information on a given
discussions, PD =(VDD × IDD) + PI/O, where PI/O is the power dissipation of the I/O drivers.
4.1
Estimation with Junction-to-Ambient Thermal Resistance
An estimation of the chip junction temperature, T
J, in
C can be obtained from the following equation:
TJ = TA + (RθJA × PD)
where:
TA = ambient temperature (C)
RθJA = package junction-to-ambient thermal resistance (C/W)
PD = 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 TJ – TA) are possible.
4 V
IL for IIC interface does not match IIC standard, but does meet IIC standard for VOL and should not cause any compatibility
issue.
5 MPC8280, MPC8275VR, MPC8275ZQ only.
Table 6. Thermal Characteristics
Characteristic
Symbol
Value
Unit
Air Flow
480 TBGA
516 PBGA
Junction to ambient—
single-layer board1
1 Assumes no thermal vias
RθJA
16
27
°C/W
Natural convection
11
21
1 m/s
Junction to ambient—
four-layer board
RθJA
12
19
°C/W
Natural convection
916
1 m/s
Junction to board2
2 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.
RθJB
611
°C/W
—
Junction to case3
3 Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL SPEC-883 Method
1012.1).
RθJC
28
°C/W
—
Junction-to-package top4
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.
Ψ
JT
22
°C/W
—