Freescale Semiconductor MC68332 - Thermal Characteristics

MC68332 ELECTRICAL CHARACTERISTICS
USER’S MANUAL A-3
Notes:
The average chip-junction temperature (T
J
) in C can be obtained from:
T
J
= T
A
+ (P
D
× Θ
JA
) (1)
where
T
A
= Ambient Temperature, °C
Θ
JA
= 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:
P
D
= K ÷ (T
J
+ 273°C) (2)
Solving equations 1 and 2 for K gives:
K = P
D
+ (T
A
+ 273°C) + Θ
JA
× P
D
2
(3)
where K is a constant pertaining to the particular part. K can be determined from equation (3) by measuring
P
D
(at equilibrium) for a known T
A
. Using this value of K, the values of P
D
and T
J
can be obtained by solving
equations (1) and (2) iteratively for any value of T
A
.
Table A-3 Thermal Characteristics
Num Rating Symbol Value Unit
1 Thermal Resistance
Plastic 132-Pin Surface Mount
Plastic 144-Pin Surface Mount
Thin Plastic 144-Pin Surface Mount
Θ
JA
38
46
49
°C/W
Fr
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Freescale Semiconductor, Inc.
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