MC9S08GT16A Datasheet, PDF (261/300 Pages) Freescale Semiconductor, Inc – Microcontrollers

Electrical Characteristics
Table A-3. Thermal Characteristics
Rating
Symbol
Value
Unit
Operating temperature range
(packaged)
T_A
T_L to T_H
–40 to 125
°C
Thermal resistance
1s board type
48-pin QFN
44-pin QFP
42-pin SDIP
θ_JA1, ²
84
72
°C/W
62
32-pin QFN
99
Thermal resistance
2s2p board type
48-pin QFN
44-pin QFP
42-pin SDIP
θ_JA1,2
26
54
°C/W
51
32-pin QFN
33
1 _{Junction temperature is a function of die size, on-chip power dissipation, package}
thermal resistance, mounting site (board) temperature, ambient temperature, airflow,
power dissipation of other components on the board, and board thermal resistance.
2 _{Per SEMI G38-87 and JEDEC JESD51-2 with the single layer board horizontal.}
Single layer board is designed per JEDEC JESD51-3.
The average chip-junction temperature (T_J) in °C can be obtained from:
T_J = T_A + (P_D × θ_JA)
Eqn. A-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:
P_D = K ÷ (T_J + 273°C)
Solving equations 1 and 2 for K gives:
Eqn. A-2
K = P_D × (T_A + 273°C) + θ_JA × (P_D)²
Eqn. A-3
where K is a constant pertaining to the particular part. K can be determined from equation 3 by measuring
P_D (at equilibrium) for a known T_A. Using this value of K, the values of P_D and T_J can be obtained by
solving equations 1 and 2 iteratively for any value of T_A.
MC9S08GT16A/GT8A Data Sheet, Rev. 1
Freescale Semiconductor
261