MC68HC11G5 Datasheet, PDF (168/195 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcontroller

Freescale Semiconductor, Inc.
13.2 THERMAL CHARACTERISTICS
Characteristic
Thermal Resistance Plastic
Symbol
θ_JA
Value
50
Unit
°C/W
13.3 POWER CONSIDERATIONS
The average chip junction temperature, T_J, in degrees Celsius can be obtained from the following
equation:
T_J= T_A + (P_D • θ_JA )
(1)
Where:
T_A =
θ_JA =
P_D =
P_INT =
P_I/O =
Ambient temperature (oC)
Package thermal resistance, junction-to-ambient (oC/W)
P_INT + P_I/O
Internal chip power = I_DD x V_DD (W)
Power dissipation on input and output pins (W) — user determined)
Note: For most applications P_I/O < P_INT and can be neglected.
An approximate relationship between P_D and TJ (if P_I/O is neglected) is:
P_D= K ÷ (T_J + 273^oC)
(2)
Solving equations (1) and (2) for K gives:
K = P_D • (T_A+ 273^oC) + θ_JA • P_D²
(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 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) for any value of T_A.
13-2
ELECTRICAL SPECIFICATIONS
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