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MC68HC05L28 Datasheet, PDF (126/156 Pages) Motorola, Inc – Flexible general-purpose microcomputer
12.2
Thermal characteristics and power considerations
Table 12-2 Package thermal characteristics
Characteristics
Thermal Resistance
– Plastic 56-pin SDIP
Symbol Value Unit
θJA
TBD °C/W
The average chip junction temperature, TJ, in degrees Celcius can be obtained from the following
equation:
TJ = TA + (PD • θJA)
[1]
where:
TA = Ambient Temperature (°C)
θJA = Package Thermal Resistance, Junction-to-ambient (°C/W)
PD = PINT + PI/O (W)
PINT = Internal Chip Power = IDD • VDD (W)
PI/O = Power Dissipation on Input and Output pins (User determined)
An approximate relationship between PD and TJ (if PI/O is neglected) is:
PD = T----J----+--K---2---7----3--
[2]
Solving equations [1] and [2] for K gives:
K = PD • (TA + 273) + θJA • PD2
[3]
where K is a constant for a particular part. K can be determined by measuring PD (at equilibrium)
for a known TA. Using this value of K, the values of PD and TJ can be obtained for any value of TA
by solving the above equations. The package thermal characteristics are shown in Table 12-2.
12
Pins
R1
R2
C
PA0–7, PB0–7 3.26k Ω 2.38kΩ 50pF
VDD = 4.5 V
R2
Test
Point
C
R1
MOTOROLA
12-2
Figure 12-1 Equivalent test load
ELECTRICAL SPECIFICATIONS
TPG
MC68HC05L28