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| MC9S08QE32_09 Datasheet, PDF (11/46 Pages) Freescale Semiconductor, Inc – 8-Bit HCS08 Central Processor Unit (CPU) | |||
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Table 4. Thermal Characteristics
Rating
Operating temperature range
(packaged)
Maximum junction temperature
Thermal resistance
Single-layer board
48-pin QFN
44-pin LQFP
32-pin LQFP
28-pin SOIC
Thermal resistance
Four-layer board
48-pin QFN
44-pin LQFP
32-pin LQFP
28-pin SOIC
Symbol
TA
TJM
θJA
Value
TL to TH
â40 to 85
95
81
68
66
57
26
46
θJA
54
42
Electrical Characteristics
Unit
°C
°C
°C/W
°C/W
The average chip-junction temperature (TJ) in °C can be obtained from:
TJ = TA + (PD à θJA)
Eqn. 1
where:
TA = Ambient temperature, °C
θJA = Package thermal resistance, junction-to-ambient, °C/W
PD = Pint + PI/O
Pint = IDD Ã VDD, Watts â chip internal power
PI/O = Power dissipation on input and output pins â user determined
For most applications, PI/O << Pint and can be neglected. An approximate relationship between PD and TJ
(if PI/O is neglected) is:
PD = K ÷ (TJ + 273°C)
Eqn. 2
Solving Equation 1 and Equation 2 for K gives:
K = PD à (TA + 273°C) + θJA à (PD)2
Eqn. 3
where K is a constant pertaining to the particular part. K can be determined from equation 3 by measuring
PD (at equilibrium) for a known TA. Using this value of K, the values of PD and TJ can be obtained by
solving Equation 1 and Equation 2 iteratively for any value of TA.
MC9S08QE32 Series MCU Data Sheet, Rev. 6
Freescale Semiconductor
11
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