Electrical Characteristics
MC9RS08KB12 Series MCU Data Sheet, Rev. 3
Freescale Semiconductor
7
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. In order to take PI/O into account in power calculations, determine the difference between
actual pin voltage and VSS or VDD 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 VSS or VDD will be very
small.
The average chip-junction temperature (TJ) in
°C can be obtained from:
TJ = TA + (PD × θJA)
Eqn. 1
where:
TA = Ambient temperature, °C
θJA = Package thermal resistance, junction-to-ambient, °C /W
PD = Pint + PI/O
Pint = IDD × VDD, Watts chip internal power
PI/O = Power dissipation on input and output pins user determined
Storage temperature range
Tstg
–55 to 150
°C
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 (VDD) and negative (VSS) clamp voltages, then use the larger of the two
resistance values.
2 All functional non-supply pins are internally clamped to V
SS and VDD except the RESET/VPP pin which is internally
clamped to VSS only.
3 Power supply must maintain regulation within operating V
DD range during instantaneous and operating maximum
current conditions. If positive injection current (VIn > VDD) is greater than IDD, the injection current may flow out of VDD
and could result in external power supply going out of regulation. Ensure external VDD 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)
TA
TL to TH
–40 to 85
°C
Maximum junction temperature
TJMAX
150
°C
Thermal resistance 20-pin SOIC
θ
JA
83
°C/W
Thermal resistance 16-pin SOIC NB
θ
JA
103
°C/W
Thermal resistance 16-pin TSSOP
θ
JA
29
°C/W
Thermal resistance 8-pin SOIC
θ
JA
150
°C/W
Thermal resistance 8-pin DFN
θ
JA
110
°C/W
Table 3. Absolute Maximum Ratings (continued)
Rating
Symbol
Value
Unit