
Electrical Characteristics
11-2
MC68307 USER’S MANUAL
MOTOROLA
11.3 POWER CONSIDERATIONS
The average chip-junction temperature, TJ, in °C can be obtained from:
TJ = TA + (PD θJA)
(1)
where:
TA = Ambient Temperature, °C
θJA = Package Thermal Resistance, Junction-to-Ambient, °C/W
PD =PINT + PI/O
PINT =ICC x VCC, 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.
An approximate relationship between PD and TJ (if PI/O is neglected) 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 thermal equilibrium) for a known TA. Using this value of K, the val-
ues of PD and TJ can be obtained by solving equations (1) and (2) iteratively for any value
of TA.
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 lev-
els specified in that figure. Outputs are specified with minimum and/or maximum limits, as
appropriate, and are measured as shown in
Figure 11-1. Inputs are specified with minimum
setup and hold times and are measured as shown. Finally, the measurement for signal-to-
signal specifications is also shown.
NOTE
The testing levels used to verify conformance to the AC specifi-
cations do not affect the guaranteed DC operation of the device
as specified in the DC electrical specifications.