Datasheet

Electrical Characteristics
MC9S08LL16 Series MCU Data Sheet, Rev. 7
Freescale Semiconductor 11
3.4 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
× θ
JA
) Eqn. 3-1
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) Eqn. 3-2
Solving Equation 3-1 and Equation 3-2 for K gives:
K = P
D
× (T
A
+ 273°C) + θ
JA
× (P
D
)
2
Eqn. 3-3
Table 5. Thermal Characteristics
Rating Symbol Value Unit
Operating temperature range
(packaged)
T
A
T
L
to T
H
–40 to 85
°C
Maximum junction temperature T
JM
95 °C
Thermal resistance
Single-layer board
64-pin LQFP
θ
JA
72
°C/W48-pin QFN 84
48-pin LQFP 81
Thermal resistance
Four-layer board
64-pin LQFP
θ
JA
54
°C/W48-pin QFN 30
48-pin LQFP 57