Freescale Semiconductor, Inc.
11.3 POWER CONSIDERATIONS
The average chip-junction temperature, T , in °C can be obtained from:
J
T = T + (P • θ )
JA
(1)
J
A
D
where:
T
= Ambient Temperature, °C
= Package Thermal Resistance, Junction-to-Ambient, °C/W
= P + P
A
θ
JA
P
P
P
D
INT
I/O
INT
I/O
= I
x V , Watts—Chip Internal Power
CC
CC
= Power Dissipation on Input and Output Pins—User Determined
For most applications, P
< P and can be neglected.
I/O
INT
An approximate relationship between P and T (if P is neglected) is:
I/O
D
J
P = K ÷ (T + 273°C)
D
J
Solving Equations (1) and (2) for K gives:
2
K = P • (T + 273°C) + θ
• P
D
D
A
JA
where K is a constant pertaining to the particular part. K can be determined from equation
(3) by measuring P (at thermal equilibrium) for a known T . Using this value of K, the
D
A
values of P and T can be obtained by solving Equations (1) and (2) iteratively for any
D
J
value of T .
A
11.4 AC ELECTRICAL SPECIFICATION DEFINITIONS
The AC specifications presented consist of output delays, input setup and hold times, and
signal skew times. All signals are specified relative to an appropriate edge of the clock and
possibly to one or more other signals.
The measurement of the AC specifications is defined by the waveforms shown in Figure
11-1. To test the parameters guaranteed by Motorola, inputs must be driven to the voltage
levels specified in the figure. Outputs are specified with minimum and/or maximum limits,
as appropriate, and are measured as shown. Inputs are specified with minimum setup and
hold times and are measured as shown. Finally, the measurement for signal-to-signal
specifications are shown.
Note that the testing levels used to verify conformance to the AC specifications do not
affect the guaranteed DC operation of the device as specified in the DC electrical
characteristics.
11-2
MC68340 USER’S MANUAL
MOTOROLA
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