74LS123.pdf

March 1991

DM74LS123 Dual Retriggerable One-Shot

with Clear and Complementary Outputs

General Description

The DM74LS123 is a dual retriggerable monostable multivi-

brator capable of generating output pulses from a few nano-

seconds to extremely long duration up to 100% duty cycle.

Each device has three inputs permitting the choice of either

leading edge or trailing edge triggering. Pin (A) is an active-

low transition trigger input and pin (B) is an active-high tran-

sition trigger input. The clear (CLR) input terminates the out-

put pulse at a predetermined time independent of the timing

components. The clear input also serves as a trigger input

when it is pulsed with a low level pulse transition ( ß ). To

obtain the best trouble free operation from this device

please read the operating rules as well as the NSC one-shot

application notes carefully and observe recommendations.

Y Compensated for V CC and temperature variations

Y Triggerable from CLEAR input

Y DTL, TTL compatible

Y Input clamp diodes

Functional Description

The basic output pulse width is determined by selection of

an external resistor (R X ) and capacitor (C X ). Once triggered,

the basic pulse width may be extended by retriggering the

gated active-low transition or active-high transition inputs or

be reduced by use of the active-low or CLEAR input. Retrig-

gering to 100% duty cycle is possible by application of an

input pulse train whose cycle time is shorter than the output

cycle time such that a continuous ``HIGH'' logic state is

maintained at the ``Q'' output.

Features

Y DC triggered from active-high transition or active-low

transition inputs

Y Retriggerable to 100% duty cycle

Connection Diagram

Function Table

Dual-In-Line Package

Inputs

Outputs

CLEAR

u Éß

H Éß

HHigh Logic Level

L e Low Logic Level

X e Can Be Either Low or High

u e Positive Going Transition

v e Negative Going Transition

É e A Positive Pulse

ß e A Negative Pulse

TL/F/6386±1

Order Number DM74LS123M or DM74LS123N

See NS Package Number M16A or N16E

C 1995 National Semiconductor Corporation

TL/F/6386

RRD-B30M105/Printed in U. S. A.

Absolute Maximum Ratings (Note)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales

Office/Distributors for availability and specifications.

Supply Voltage

Note: The ``AbsoluteMaximumRatings'' are those values

beyondwhich the safety of thedevice cannot be guaran-

teed.Thedeviceshouldnotbeoperatedattheselimits.The

parametricvaluesdefinedinthe``ElectricalCharacteristics''

tablearenotguaranteedattheabsolutemaximumratings.

The``RecommendedOperatingConditions''tablewilldefine

theconditionsforactualdeviceoperation.

Input Voltage

Operating Free Air Temperature Range

0 § Cto a 70 § C

Storage Temperature

b 65 § Cto a 150 § C

Recommended Operating Conditions

Symbol

Parameter

Min

Nom Max

Units

V CC

Supply Voltage

4.75

5.25

V IH

High Level Input Voltage

V IL

Low Level Input Voltage

0.8

I OH

High Level Output Current

b 0.4

I OL

Low Level Output Current

t W

Pulse Width

A or B High

(Note 6)

A or B Low

Clear Low

R EXT

External Timing Resistor

260

k X

C EXT

External Timing Capacitance

No Restriction

m F

C WIRE

Wiring Capacitance

at R EXT /C EXT Terminal

T A

Free Air Operating Temperature

§ C

Electrical Characteristics over recommended operating free air temperature range (unless otherwise noted)

Symbol

Parameter

Conditions

Min

Typ

Max Units

(Note 1)

V I

Input Clamp Voltage

V CC e Min, I I eb 18 mA

b 1.5

V OH

High Level Output

V CC e Min, I OH e Max

2.7

3.4

Voltage

V IL e Max, V IH e Min

V OL

Low Level Output

V CC e Min, I OL e Max

0.35

0.5

Voltage

V IL e Max, V IH e Min

I OL e 4 mA, V CC e Min

0.25

0.4

I I

Input Current @ Max

V CC e Max, V I e 7V

0.1

Input Voltage

I IH

High Level Input Current V CC e Max, V I e 2.7V

m A

I IL

Low Level Input Current

V CC e Max, V I e 0.4V

b 0.4 mA

I OS

Short Circuit

V CC e Max

b 20

b 100 mA

Output Current

(Note 2)

I CC

Supply Current

V CC e Max (Notes 3,4 and 5)

Note 1: All typicals are at V CC e 5V, T A e 25 § C.

Note 2: Not more than one output should be shorted at a time, and the duration should not exceed one second.

Note 3: Quiescent I CC is measured (after clearing) with 2.4V applied to all clear and A inputs, B inputs grounded, all outputs open, C EXT e 0.02 m F, and

R EXT e 25 k X .

Note 4: I CC is measured in the triggered state with 2.4V applied to all clear and B inputs, A inputs grounded, all outputs open, C EXT e 0.02 m F, and R EXT e 25 k X .

Note 5: With all outputs open and 4.5V applied to all data and clear inputs, ICC is measured after a momentary ground, then 4.5V is applied to the clock.

Note 6: TA e 25 § C and VCC e 5V.

Switching Characteristics at V CC e 5V and T A e 25 § C

R L e 2k X

Symbol

Parameters

From (Input)

C L e 15pF

Units

To (Output) C EXT e 0 pF, R EXT e 5k X C EXT e 1000 pF, R EXT e 10 K X

Min

Max

Min

Max

t PLH Propagation Delay Time

AtoQ

Low to High Level Output

t PLH Propagation Delay Time

BtoQ

Low to High Level Output

t PHL Propagation Delay Time

AtoQ

High to Low Level Output

t PHL Propagation Delay Time

BtoQ

High to Low Level Output

t PLH Propagation Delay Time

Clear to Q

Low to High Level Output

t PHL Propagation Delay Time

Clear to Q

High to Low Level Output

t WQ(Min) Minimum Width of Pulse

AorBtoQ

200

at Output Q

t W(out) Output Pulse Width

A or B to Q

m s

Operating Rules

1. An external resistor (R X ) and an external capacitor (C X )

are required for proper operation. The value of C X may

vary from 0 to any necessary value. For small time con-

stants high-grade mica, glass, polypropylene, polycarbon-

ate, or polystyrene material capacitors may be used. For

large time constants use tantalum or special aluminum

capacitors. If the timing capacitors have leakages ap-

proaching 100 nA or if stray capacitance from either ter-

minal to ground is greater than 50 pF the timing equations

may not represent the pulse width the device generates.

2. When an electrolytic capacitor is used for C X a switching

diode is often required for standard TTL one-shots to pre-

vent high inverse leakage current. This switching diode is

not needed for the 'LS123 one-shot and should not be

used. In general the use of the switching diode is not

recommended with retriggerable operation.

Furthermore, if a polarized timing capacitor is used on the

'LS123 the negative terminal of the capacitor should be

connected to the ``C EXT '' pin of the device (Figure1).

3. For C X ll 1000 pF the output pulse width (T W )isde-

fined as follows:

T W e KR X C X

where [ R X is in k X ]

[C X is in pF]

[T W is in ns]

K & 0.37

4. The multiplicative factor K is plotted as a function of C X

below for design considerations:

TL/F/6386±2

FIGURE 2

TL/F/6386±8

FIGURE 1

Operating Rules (Continued)

5. For C X k 1000 pF see Figure 3 for T W vs C X family

curves with R X as a parameter:

TL/F/6386±7

TL/F/6386±3

FIGURE 7

9. Under any operating condition C X and R X must be kept

as close to the one-shot device pins as possible to mini-

mize stray capacitance, to reduce noise pick-up, and to

reduce I-R and Ldi/dt voltage developed along their

connecting paths. If the lead length from C X to pins (6)

and (7) or pins (14) and (15) is greater than 3 cm, for

example, the output pulse width might be quite different

from values predicted from the appropriate equations. A

non-inductive and low capacitive path is necessary to

ensure complete discharge of C X in each cycle of its

operation so that the output pulse width will be accurate.

10. The C EXT pins of this device are internally connected to

the internal ground. For optimum system performance

they should be hard wired to the system's return ground

plane.

11. V CC and ground wiring should conform to good high-fre-

quency standards and practices so that switching tran-

sients on the V CC and ground return leads do not cause

interaction between one-shots. A 0.01 m F to 0.10 m F

bypass capacitor (disk ceramic or monolithic type) from

V CC to ground is necessary on each device. Further-

more, the bypass capacitor should be located as close

to the V CC -pin as space permits.

For further detailed device characteristics and output performance

please refer to the NSC one-shot application note AN-372.

FIGURE 3

6. To obtain variable pulse widths by remote trimming, the

following circuit is recommended:

TL/F/6386±4

FIGURE 4

Note: ``R remote '' should be as close to the device pin as possible.

7. The retriggerable pulse width is calculated as shown be-

low:

T e T W a t PLH e K c R X c C X a t PLH

The retriggered pulse width is equal to the pulse width

plus a delay time period (Figure5).

TL/F/6386±5

FIGURE 5

8. Output pulse width variation versus V CC and tempera-

tures: Figure 6 depicts the relationship between pulse

width variation versus V CC , and Figure 7 depicts pulse

width variation versus temperatures.

TL/F/6386±6

FIGURE 6

Physical Dimensions inches (millimeters)

16-Lead Small Outline Molded Package

Order Number DM74LS123M

NS Package Number M16A

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