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MC68HC705C9A Datasheet, PDF (94/118 Pages) Motorola, Inc – Microcontrollers | |||
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Electrical Specifications
12.4 Power Considerations
The average chip-junction temperature, TJ, in °C, can be obtained from:
TJ = TA + (PD à θJA)
(1)
where:
TA = Ambient temperature, °C
θJA = Package thermal resistance, junction to ambient, °C/W
PD = PINT + PI/O
PINT = IDD Ã VDD watts (chip internal power)
PI/O = Power dissipation on input and output pins (user determined)
For most applications PI/O « PINT and can be neglected.
The following is an approximate relationship between PD and TJ (neglecting PJ):
PD = K ÷ (TJ + 273 °C)
(2)
Solving equations (1) and (2) for K gives:
K = PD à (TA + 273 °C) + θJA à (PD)2
(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.
TEST
POINT
VDD
R2
SEE TABLE
C
(SEE TABLE)
R1
(SEE TABLE)
VDD = 4.5 V
Pins
PA7âPA0
PB7âPB0
PC7âPC0
PD5âPD0, PD7
R1
R2
C
3.26 â¦
2.38 ⦠50 pF
VDD = 3.0 V
Pins
PA7âPA0
PB7âPB0
PC7âPC0
PD5âPD0, PD7
R1
R2
C
10.91 ⦠6.32 ⦠50 pF
Figure 12-1. Test Load
MC68HC05C9A Advance Information Data Sheet, Rev. 4.1
94
Freescale Semiconductor
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