
Electrical Specifications
Thermal Characteristics
MC68HC705K1 — Rev. 2.0
Technical Data
Electrical Specifications
12.5 Thermal Characteristics
12.6 Power Considerations
The average chip junction temperature, TJ, in °C can be obtained from:
TJ = TA + (PD x θJA)
(1)
Where:
TA = ambient temperature in °C
θ
JA = package thermal resistance, junction to ambient in °C/W
PD = PINT + PI/O
PINT = ICC × VCC = chip internal power dissipation
PI/O = power dissipation on input and output pins (user-determined)
For most applications, PI/O < PINT and can be neglected.
Ignoring PI/O, the relationship between PD and TJ is approximately:
(2)
Solving equations (1) and (2) for K gives:
= PD x (TA + 273°C) + θJA x (PD)
2
(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 equations (1) and (2) iteratively for any value of TA.
Characteristic
Symbol
Value
Unit
Maximum junction temperature
TJ
150
°C
Thermal resistance
MC68HC705K1P(1)
MC68HC705K1DW(2)
1. P = Plastic dual in-line package (PDIP)
2. DW = Small outline integrated circuit (SOIC)
θ
JA
100
140
°C/W
PD =
TJ + 273°C
K
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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