Datasheet
MC9S08MP16 Series Data Sheet, Rev. 2
Electrical Characteristics
Freescale Semiconductor10
2.4 Thermal Characteristics
This section provides information about operating temperature range, power dissipation, and package thermal resistance. Power
dissipation on I/O pins is usually small compared to the power dissipation in on-chip logic and voltage regulator circuits, and
it is user-determined rather than being controlled by the MCU design. To take P
I/O
into account in power calculations, determine
the difference between actual pin voltage and V
SS
or V
DD
and multiply by the pin current for each I/O pin. Except in cases of
unusually high pin current (heavy loads), the difference between pin voltage and V
SS
or V
DD
will be very small.
The average chip-junction temperature (T
J
) in C can be obtained from:
T
J
= T
A
+ (P
D
JA
) Eqn. 1
where:
T
A
= Ambient temperature, C
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
+ 273C) Eqn. 2
Solving Equation 1 and Equation 2 for K gives:
K = P
D
(T
A
+ 273C) +
JA
(P
D
)
2
Eqn. 3
Table 4. Thermal Characteristics
Num C Rating Symbol
Consumer &
Industrial
Automotive Unit
1 — Operating temperature range (packaged) T
A
–40 to 105 –40 to 125 C
2 D Maximum junction temperature T
J
115 135 C
3 D Thermal resistance
1,2
single-layer board
1
Junction temperature is a function of die size, on-chip power dissipation, package thermal resistance, mounting site (board)
temperature, ambient temperature, air flow, power dissipation of other components on the board, and board thermal
resistance.
2
Junction-to-ambient natural convection
48-pin LQFP
JA
80 80
C/W32-pin LQFP 85 —
28-pin SOIC 71 —
4 D Thermal resistance
1,2
four-layer board
48-pin LQFP
JA
56 56
C/W32-pin LQFP 57 —
28-pin SOIC 48 —