MC9S08PA16 Datasheet, PDF (17/33 Pages) Freescale Semiconductor, Inc – MC9S08PA16 Series

Rating
44-pin LQFP
32-pin LQFP
20-pin SOIC
20-pin TSSOP
16-pin TSSOP
Peripheral operating requirements and behaviors
Table 8. Thermal characteristics (continued)
Symbol
Value
Thermal resistance four-layer board
θ_JA
54
θ_JA
59
θ_JA
54
θ_JA
76
θ_JA
87
Unit
°C/W
°C/W
°C/W
°C/W
°C/W
The average chip-junction temperature (T_J) in °C can be obtained from:
T_J = T_A + (P_D × θ_JA)
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)
Solving the equations above for K gives:
K = P_D × (T_A + 273 °C) + θ_JA × (P_D)²
where K is a constant pertaining to the particular part. K can be determined by measuring
P_D (at equilibrium) for an known T_A. Using this value of K, the values of P_D and T_J can
be obtained by solving the above equations iteratively for any value of T_A.
6 Peripheral operating requirements and behaviors
MC9S08PA16 Series Data Sheet, Rev. 1, 10/9/2012.
Freescale Semiconductor, Inc.
17