MC68340 datasheet(402/441 Pages) FREESCALE

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11-2

MC68340 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:

= Ambient Temperature,

°C

θJA

= Package Thermal Resistance, Junction-to-Ambient,

°C/W

=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)

Solving Equations (1) and (2) for K gives:

K = PD • (TA + 273°C) + θJA • PD2

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

values 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

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.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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