MC68HC11P2 Datasheet, PDF (233/268 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Electrical Specifications
Thermal characteristics and power considerations
12.4 Thermal characteristics and 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 = Ambient temperature (°C)
θ_JA = Package thermal resistance, junction-to-ambient (°C/W)
P_D = Total power dissipation = P_INT + P_I/O (W)
P_INT = Internal chip power = I_DD • V_DD (W)
P_I/O = Power dissipation on input and output pins (User determined)
An approximate relationship between P_D and T_J (if P_I/O is neglected) is:
P_D = _T-----_J---+-^K----2---7---3-
[2]
Solving equations [1] and [2] for K gives:
K = P_D • (T_A + 273) + θ_JA • P_D²
[3]
where K is a constant for a particular part. K can be determined 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 for any value of T_A, by solving the
above equations. The package thermal characteristics are shown
below:
Characteristics
Thermal resistance
– 84-pin PLCC package
– 84-pin CERQUAD package (EPROM)
– 88-pin QFP package
Symbol
θ_JA
Value
50
50
TBD
Unit
°C/W
MC68HC11P2 — Rev 1.0
Electrical Specifications
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Technical Data