MC9S08AC128 Datasheet, PDF (13/42 Pages) Freescale Semiconductor, Inc – 8-Bit Microcontroller

Chapter 3 Electrical Characteristics and Timing Specifications
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 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.
Table 3-3. Thermal Characteristics
Rating
Operating temperature range (packaged)
Maximum junction temperature
Thermal resistance ^1,2,3,4
Symbol
T_A
T_J
Value
T_L to T_H
–40 to 125
150
Unit
°C
°C
80-pin LQFP
64-pin QFP
1s
2s2p
1s
θ_JA
2s2p
61
47
57
°C/W
43
44-pin LQFP
1s
73
2s2p
56
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}
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:
Solving equations 1 and 2 for K gives:
P_D = K ÷ (T_J + 273°C)
Eqn. 3-2
MC9S08AC128 MCU Series Data Sheet, Rev. 1
Freescale Semiconductor
13
Preliminary — Subject to Change