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S9S08SG8E2MSC Datasheet, PDF (290/320 Pages) Freescale Semiconductor, Inc – MC9S08SG8 MC9S08SG4 Data Sheet Addendum | |||
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Appendix A Electrical Characteristics
The average chip-junction temperature (TJ) in ï°C can be obtained from:
where:
TJ = TA + (PD ï´ ï±JA)
Eqn. A-1
TA = Ambient temperature, ï°Cï
ï±JA = Package thermal resistance, junction-to-ambient, ï°C/Wï
PD = Pint ï«ï PI/Oï
Pint = IDD ï´ VDD, Watts â chip internal powerï
PI/O = Power dissipation on input and output pins â user determined
For most applications, PI/O ï¼ï¼ Pint and can be neglected. An approximate relationship between PD and TJ
(if PI/O is neglected) is:
PD = K ï¸ (TJ + 273ï°C)
Solving Equation A-1 and Equation A-2 for K gives:
Eqn. A-2
K = PD ï´ (TA + 273ï°C) + ï±JA ï´ (PD)2
Eqn. A-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 A-1 and Equation A-2 iteratively for any value of TA.
MC9S08SG8 MCU Series Data Sheet, Rev. 7
286
Freescale Semiconductor
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