Freescale Semiconductor MC9S08PA32, Технические данные инструкция

Страница: 17 / 35

Table 8. Thermal characteristics (continued)
Rating Symbol Value Unit
Thermal resistance four-layer board
64-pin LQFP
θ
JA
53 °C/W
64-pin QFP
θ
JA
47 °C/W
48-pin LQFP
θ
JA
57 °C/W
44-pin LQFP
θ
JA
53 °C/W
32-pin LQFP
θ
JA
57 °C/W
The average chip-junction temperature (T
J
) in °C can be obtained from:
T
J
= T
A
+ (P
D
×
θ
JA
)
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)
Solving the equations above for K gives:
K = P
D
× (T
A
+ 273 °C) +
θ
JA
× (P
D
)
2
where K is a constant pertaining to the particular part. K can be determined by measuring
P
D
(at equilibrium) for an known T
A
. Using this value of K, the values of P
D
and T
J
can
be obtained by solving the above equations iteratively for any value of T
A
.
6 Peripheral operating requirements and behaviors
Peripheral operating requirements and behaviors
MC9S08PA60 Series Data Sheet, Rev. 1, 10/9/2012.
Freescale Semiconductor, Inc. 17