Datasheet

Electrical Characteristics
MC9S08QE128 Series Data Sheet, Rev. 7
Freescale Semiconductor 13
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. 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
3
Power supply must maintain regulation within operating V
DD
range during instantaneous and
operating maximum current conditions. If positive injection current (V
In
> V
DD
) is greater than
I
DD
, the injection current may flow out of V
DD
and could result in external power supply going
out of regulation. Ensure external V
DD
load will shunt current greater than maximum injection
current. This will be the greatest risk when the MCU is not consuming power. Examples are: if
no system clock is present, or if the clock rate is very low (which would reduce overall power
consumption).
Table 5. Thermal Characteristics
Rating Symbol Value Unit
Operating temperature range (packaged) T
A
–40 to 85 °C
Maximum junction temperature T
JM
95 °C
Thermal resistance
Single-layer board
32-pin LQFP
θ
JA
82
°C/W44-pin LQFP 68
48-pin QFN 81
64-pin LQFP
θ
JA
69
°C/W
80-pin LQFP 60
Thermal resistance
Four-layer board
32-pin LQFP
θ
JA
54
°C/W44-pin LQFP 46
48-pin QFN 26
64-pin LQFP
θ
JA
50
°C/W
80-pin LQFP 47