Datasheet

Electrical Characteristics
MC9S08JS16 Series MCU Data Sheet, Rev. 4
Freescale Semiconductor 7
3.3 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 it is user-determined rather than being controlled by the MCU design. In order 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
1
Input must be current limited to the value specified. To determine the value of the required
current-limiting resistor, calculate resistance values for positive (V
DD
) and negative (V
SS
) clamp
voltages, then use the larger of the two resistance values.
2
All functional non-supply pins are internally clamped to V
SS
and V
DD
.
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 4. Thermal Characteristics
Rating Symbol Value Unit
Operating temperature range (packaged)
T
A
T
L
to T
H
-40 to 85
°C
Thermal resistance
1,2,3,4
24-pin QFN
1s
2s2p
20-pin SOIC
1s
2s2p
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
3
1s — Single layer board, one signal layer
4
2s2p — Four layer board, 2 signal and 2 power layers
θ
JA
92
33
86
58
°C/W