74HC datasheet(15/19 Pages) PHILIPS

15 / 19 page

March 1988

Philips Semiconductors

HCMOS family characteristics

FAMILY SPECIFICATIONS

DATA SHEET SPECIFICATION GUIDE

INTRODUCTION

The 74HCMOS data sheets have been designed for

ease-of-use. A minimum of cross-referencing for more

information is needed.

TYPICAL PROPAGATION DELAY AND FREQUENCY

The typical propagation delays listed at the top of the data

sheets are the average of tPLH and tPHL for the longest data

path through the device with a 15 pF load.

For clocked devices, the maximum frequency of operation

is also given. The typical operating frequency is the

maximum device operating frequency with a 50% duty

factor and no constraints on tr and tf.

LOGIC SYMBOLS

Two logic symbols are given for each device - the

conventional one (Logic Symbol) which explicitly shows

the internal logic (except for complex logic) and the IEC

Logic Symbol as developed by the IEC (International

Electrotechnical Commission).

The IEC has been developing a very powerful symbolic

language that can show the relationship of each input of a

digital logic current to each output without explicitly

showing the internal logic.

Internationally, Working Group 2 of IEC Technical

Committee TC-3 has prepared a new document

(Publication 617-12) which supersedes

Publication 117-15, published in 1972.

RATINGS

The “RATINGS” table (Limiting values in accordance with

the Absolute Maximum System - IEC134) lists the

maximum limits to which the device can be subjected

without damage. This doesn’t imply that the device will

function at these extreme conditions, only that, when these

conditions are removed and the device operated within the

Recommended Operating Conditions, it will still be

functional and its useful life won’t have been shortened.

The maximum rated supply voltage of 7 V is well below the

typical breakdown voltage of 18 V.

RECOMMENDED OPERATING CONDITIONS

The “RECOMMENDED OPERATING CONDITIONS”

table lists the operating ambient temperature and the

conditions under which the limits in the “DC

CHARACTERISTICS” and “AC CHARACTERISTICS”

tables will be met. The table should not be seen as a set of

limits guaranteed by the manufacturer, but as the

conditions used to test the devices and guarantee that

they will then meet the limits in the DC and AC

CHARACTERISTICS tables.

DC CHARACTERISTICS

The “DC CHARACTERISTICS” table reflects the DC limits

used during testing. The values published are guaranteed.

The threshold values of VIH and VIL can be tested by the

user. If VIH and VIL are applied to the inputs, the output

voltages will be those published in the “DC

CHARACTERISTICS” table. There is a tendency, by

some, to use the published VIH and VIL thresholds to test a

device for functionality in a “function-table exercizer”

mode. This frequently causes problems because of the

noise present at the test head of automated test

equipment with cables up to 1 metre. Parametric tests,

such as those used for the output levels under the VIH and

VIL conditions are done fairly slowly, in the order of

milliseconds, so that there is no noise at the inputs when

the outputs are measured. But in functionality testing, the

outputs are measured much faster, so there can be noise

on the inputs, before the device has assumed its final and

correct output state. Thus, never use VIH and VIL to test the

functionality of any HCMOS device type; instead, use input

voltages of VCC (for the HIGH state) and 0 V (for the LOW

state). In no way does this imply that the devices are

noise-sensitive in the final system.

In the data sheets, it may appear strange that the typical

VIL is higher than the maximum VIL. However, this is

because VILmax is the maximum VIL (guaranteed) for all

devices that will be recognized as a logic LOW. However,

typically a higher VIL will also be recognized as a logic

LOW. Conversely, the typical VIH is lower than its minimum

guaranteed level.

For 74HCMOS, unlike TTL, no output HIGH short-circuit

current is specified. The use of this current, for example, to

calculate propagation delays with capacitive loads, is

covered by the HCMOS graphs showing the output drive

capability and those showing the dependence of

propagation delay on load capacitance.

The quiescent supply current ICC is the leakage current of

all the reversed-biased diodes and the OFF-state MOS

transistors. It is measured with the inputs at VCC or GND

and is typically a few nA.

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