(TOP VIEW)

positive logic: Low input to clear resets Q low and

14

13

12

11

10

9

1

2

3

4

5

6

7

16

15

8

VCC

1A

1 Rext/

Cext

1

Cext 1Q

2Q

2B

2

CLR

2A

1B

1

CLR

1Q

2Q

2

Cext

2 Rext/

Cext

GND

Q

Q

CLR

Q

Q

CLR

+

VCC

Rext

R/C

Cext

*See operational notes — Pulse Trigger Modes

5-380

FAST AND LS TTL DATA

DUAL MONOSTABLE

MULTIVIBRATORS

WITH SCHMITT-TRIGGER INPUTS

Each multivibrator of the LS221 features a negative-transition-triggered

input and a positive-transition-triggered input either of which can be used as

an inhibit input.

Pulse triggering occurs at a voltage level and is not related to the transition

time of the input pulse. Schmitt-trigger input circuitry for B input allows

jitter-free triggering for inputs as slow as 1 volt/ second, providing the circuit

with excellent noise immunity. A high immunity to VCC noise is also provided

by internal latching circuitry.

Once triggered, the outputs are independent of further transitions of the

inputs and are a function of the timing components. The output pulses can be

terminated by the overriding clear. Input pulse width may be of any duration

relative to the output pulse width. Output pulse width may be varied from 35

nanoseconds to a maximum of 70 s by choosing appropriate timing

components. With Rext = 2.0 kΩ and Cext = 0, a typical output pulse of 30

nanoseconds is achieved. Output rise and fall times are independent of pulse

length.

Pulse width stability is achieved through internal compensation and is

virtually independent of VCC and temperature. In most applications, pulse

stability will only be limited by the accuracy of external timing components.

Jitter-free operation is maintained over the full temperature and VCC ranges

for greater than six decades of timing capacitance (10 pF to 10

µF), and

greater than one decade of timing resistance (2.0 to 70 k

Ω for the

SN54LS221, and 2.0 to 100 k

Ω for the SN74LS221). Pulse width is defined

if Cext is in pF and Rext is in kΩ. If pulse cutoff is not critical, capacitance up

to 1000

µF and resistance as low as 1.4 kΩ may be used. The range of

jitter-free pulse widths is extended if VCC is 5.0 V and 25°C temperature.

FUNCTION TABLE

(EACH MONOSTABLE)

INPUTS

OUTPUTS

CLEAR

A

B

Q

Q

L

X

X

L

H

X

H

X

L

H

X

X

L

L

H

H

L

°

H

±

H

*

°

L

H

TYPE

TYPICAL

POWER

MAXIMUM

OUTPUT PULSE

DISSIPATION

LENGTH

SN54LS221

23 mW

49 s

SN74LS221

23 mW

70 s

SN54/74LS221

DUAL MONOSTABLE

MULTIVIBRATORS

WITH SCHMITT-TRIGGER INPUTS

LOW POWER SCHOTTKY

J SUFFIX

CERAMIC

CASE 620-09

N SUFFIX

PLASTIC

CASE 648-08

16

1

16

1

ORDERING INFORMATION

SN54LSXXXJ

Ceramic

SN74LSXXXN

Plastic

SN74LSXXXD

SOIC

16

1

D SUFFIX

SOIC

CASE 751B-03