SN74LS221
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 V
CC
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 R
ext
= 2.0 kΩ and C
ext
= 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 V
CC
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 V
CC
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 100 kΩ
for the SN74LS221). Pulse width is defined by the relationship:
t
w
(out) = C
ext
R
ext
ln 2.0
≈
0.7 C
ext
R
ext
; where t
W
is in ns if C
ext
is in
pF and R
ext
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 V
CC
is 5.0 V and 25°C
temperature.
http://onsemi.com
LOW
POWER
SCHOTTKY
16
1
PLASTIC
N SUFFIX
CASE 648
16
1
SOIC
D SUFFIX
CASE 751B
•
SN74LS221 is a Dual Highly Stable One-Shot
•
Overriding Clear Terminates Output Pulse
•
Pin Out is Identical to SN74LS123
ORDERING INFORMATION
GUARANTEED OPERATING RANGES
Symbol
V
CC
T
A
I
OH
I
OL
Parameter
Supply Voltage
Operating Ambient
Temperature Range
Output Current – High
Output Current – Low
Min
4.75
0
Typ
5.0
25
Max
5.25
70
– 0.4
8.0
Unit
V
°C
mA
mA
SN74LS221D
16 Pin
2500/Tape & Reel
Device
SN74LS221N
Package
16 Pin DIP
Shipping
2000 Units/Box
©
Semiconductor Components Industries, LLC, 1999
1
December, 1999 – Rev. 6
Publication Order Number:
SN74LS221/D
ONSEMI [ ON SEMICONDUCTOR ]
