DM74LS221 Dual Non-Retriggerable One-Shot with Clear and Complementary Outputs
February 1992
DM74LS221 Dual Non-Retriggerable One-Shot
with Clear and Complementary Outputs
General Description
The DM74LS221 is a dual monostable multivibrator with
Schmitt-trigger input Each device has three inputs permit-
ting the choice of either leading-edge or trailing-edge trig-
gering Pin (A) is an active-low trigger transition input and
pin (B) is an active-high transition Schmitt-trigger input that
allows jitter free triggering for inputs with transition rates as
slow as 1 volt second This provides the input with excellent
noise immunity Additionally an internal latching circuit at the
input stage also provides a high immunity to V
CC
noise The
clear (CLR) input can terminate the output pulse at a prede-
termined time independent of the timing components This
(CLR) input also serves as a trigger input when it is pulsed
with a low level pulse transition (
) To obtain the best
and trouble free operation from this device please read op-
erating rules as well as the NSC one-shot application notes
carefully and observe recommendations
Y
Y
Y
Y
Y
Y
Y
Pin-out identical to 鈥橪S123 (Note 1)
Output pulse width range from 30 ns to 70 seconds
Hysteresis provided at (B) input for added noise
immunity
Direct reset terminates output pulse
Triggerable from CLEAR input
DTL TTL compatible
Input clamp diodes
Note 1
The pin-out is identical to 鈥橪S123 but functionally it is not refer to
Operating Rules 10 in this datasheet
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 is independent of further input tran-
sitions and is a function of the timing components or it may
be reduced or terminated by use of the active low CLEAR
input Stable output pulse width ranging from 30 ns to 70
seconds is readily obtainable
Features
Y
Y
A dual highly stable one-shot
Compensated for V
CC
and temperature variations
Connection Diagram
Dual-In-Line Package
Function Table
Inputs
CLEAR
L
X
X
H
H
A
X
H
X
L
B
X
X
L
Q
L
L
L
Outputs
Q
H
H
H
u
H
H
v
L
u
H
e
High 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
e
A Positive Pulse
e
A Negative Pulse
TL F 6409 鈥?1
This mode of triggering requires first the B input be set from a low to high
level while the CLEAR input is maintained at logic low level Then with the B
input at logic high level the CLEAR input whose positive transition from low
to high will trigger an output pulse
Order Number DM74LS221M or DM74LS221N
See NS Package Number M16A or N16A
TL F 6409 鈥?2
C
1995 National Semiconductor Corporation
TL F 6409
RRD-B30M105 Printed in U S A
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