MC68HC05E0 Datasheet, PDF (78/96 Pages) Motorola, Inc – High-density complementary metal oxide semiconductor (HCMOS) microcontroller unit

9.3
Thermal Characteristics and Power Considerations
The average chip junction temperature, TJ, in degrees Celsius can be obtained from the following
equation:
TJ= TA + (PD • θ_JA)
Where:
TA =
θ_JA =
PD =
PINT =
PI/O =
Ambient Temperature (^οC)
Package Thermal Resistance, Junction-to-Ambient (^οC/W)
PINT + PI/O
IDD x VDD (W) = Internal Chip Power
Power Dissipation on Input and Output Pins (User Determined)
Note: 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^οC)
Solving the equations PD and TJ for K gives:
K = PD • (TA+ 273^οC) + θ_JA • PD2
9
Where K is a constant pertaining to a particular part. K can be determined by measuring PD (at
equilibrium) for known TA. Using this value of K the values of PD and TJ can be obtained by solving
the above equations for any value of TA. The package thermal characteristics are shown in Table 9-2.
Table 9-2 Thermal Characteristics
Characteristics
Thermal Resistance
Plastic 68-Pin Quad Pack (PLCC)
Symbol
θ _JA
Value
50
Unit
°C/W
Pins
R1
A12 − A0,
3.26 kΩ
PD7 − PD5,
CSROM, R/W,
CS2, CS3
R2
2.38 kΩ
C
50 pF
R2
Test
Point
C
R2
Figure 9-1 Equivalent Test Load
MOTOROLA
9-2
ELECTRICAL SPECIFICATIONS
MC68HC05E0