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| MC68LC302 Datasheet, PDF (120/169 Pages) Motorola, Inc – Low Power Integrated Multiprotocol Processor Reference Manual | |||
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Electrical Characteristics
6.3 POWER CONSIDERATIONS
The average chip-junction temperature, TJ, in °C can be obtained from:
TJ =
TA + (PD ⢠θJA)(1)
where:
TA =
θJA =
PD =
PINT =
PI/O =
Ambient Temperature, °C
Package Thermal Resistance, Junction to Ambient, °C/W
PINT + PI/O
IDD x VDD, WattsâChip Internal Power
Power Dissipation on Input and Output PinsâUser Determined
For most applications PI/O < 0.3 ⢠PINT and can be neglected.
If PI/O is neglected, an approximate relationship between PD and TJ is
PD = K ÷ (TJ + 273°C)(2)
Solving equations (1) and (2) for K gives:
K
=
PD ⢠(TA + 273°C) + θJA ⢠PD2(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.
MOTOROLA
MC68LC302 REFERENCE MANUAL
6-3
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