M68HC16 Z SERIES
ELECTRICAL CHARACTERISTICS
USER’S MANUAL
A-5
Table A-6 Thermal Characteristics
Num
Characteristic
Symbol
Value
Unit
1
Thermal Resistance
Plastic 132-Pin Surface Mount
Plastic 144-Pin Surface Mount
Θ
JA
38
49
°
C/W
The average chip-junction temperature (T
J
) in C can be obtained from:
(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:
(2)
Solving equations 1 and 2 for K gives:
(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
.
T
J
T
A
P
D
Θ
JA
×
(
)
+
=
P
D
K
T
J
273
°
C
+
(
)
÷
=
K
P
D
T
A
273
°
C
+
(
)
×
Θ
JA
P
D
2
×
+
=
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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