Motorola MCF5281 用户手册
MOTOROLA
Chapter 33. Electrical Characteristics
33-3
Thermal Characteristics
33.2 Thermal Characteristics
Table 33-2. Thermal Characteristics
Characteristic
Symbol
Value
Unit
Junction to ambient, natural convection
Four layer board (2s2p)
θ
JMA
26
1,2
1
θ
JMA
and
Ψ
jt
parameters are simulated in accordance with EIA/JESD Standard 51-2 for natural convection.
Motorola recommends the use of
θ
JA
and power dissipation specifications in the system design to prevent device
junction temperatures from exceeding the rated specification. System designers should be aware that device
junction temperatures can be significantly influenced by board layout and surrounding devices. Conformance to
the device junction temperature specification can be verified by physical measurement in the customer’s system
using the
junction temperatures can be significantly influenced by board layout and surrounding devices. Conformance to
the device junction temperature specification can be verified by physical measurement in the customer’s system
using the
Ψ
jt
parameter, the device power dissipation, and the method described in EIA/JESD Standard 51-2.
2
Per JEDEC JESD51-6 with the board horizontal.
°C/W
Junction to ambient (@200 ft/min)
Four layer board (2s2p)
θ
JMA
1,2
°C/W
Junction to board
θ
JB
15
3
3
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.
measured on the top surface of the board near the package.
°C/W
Junction to case
θ
JC
10
4
4
Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL
SPEC-883 Method 1012.1).
SPEC-883 Method 1012.1).
°C/W
Junction to top of package
Natural convection
Ψ
jt
5
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.
temperature per JEDEC JESD51-2. When Greek letters are not available, the thermal characterization parameter
is written as Psi-JT.
°C/W
The average chip-junction temperature (T
J
) in
°C can be obtained from:
(1)
Where:
T
A
= Ambient Temperature, ×C
Q
JMA
= Package Thermal Resistance, Junction-to-Ambient, ×C/W
P
D
= P
INT
+ P
I/O
P
INT
= I
DD
¥ V
DD
, Watts - Chip Internal Power
P
I/O
= Power Dissipation on Input and Output Pins — User Determined
For most applications P
I/O
< P
INT
and can be neglected. An approximate relationship
between P
D
and T
J
(if P
I/O
is neglected) is:
T
J
T
A
P
D
Θ
JMA
×
(
)
+
=