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DM74LS123 Dual Retriggerable One-Shot with Clear and Complementary Outputs
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
A
B
Q
Q
L
X
X
L
H
X
H
X
L
H
X
X
L
L
H
u
Éß
H
L
v
H
H
Éß
u
L
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
7V
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
7V
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
5.25
V
V
IH
High Level Input Voltage
2
V
V
IL
Low Level Input Voltage
0.8
V
I
OH
High Level Output Current
b
0.4
mA
I
OL
Low Level Output Current
8
mA
t
W
Pulse Width
A or B High
40
(Note 6)
A or B Low
40
ns
Clear Low
40
R
EXT
External Timing Resistor
5
260
k
X
C
EXT
External Timing Capacitance
No Restriction
m
F
C
WIRE
Wiring Capacitance
50
pF
at R
EXT
/C
EXT
Terminal
T
A
Free Air Operating Temperature
0
70
§
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
V
OH
High Level Output
V
CC
e
Min, I
OH
e
Max
2.7
3.4
V
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
V
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
mA
Input Voltage
I
IH
High Level Input Current V
CC
e
Max, V
I
e
2.7V
20
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)
12
20
mA
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.
2
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
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
33
ns
Low to High Level Output
t
PLH
Propagation Delay Time
BtoQ
44
ns
Low to High Level Output
t
PHL
Propagation Delay Time
AtoQ
45
ns
High to Low Level Output
t
PHL
Propagation Delay Time
BtoQ
56
ns
High to Low Level Output
t
PLH
Propagation Delay Time
Clear to Q
45
ns
Low to High Level Output
t
PHL
Propagation Delay Time
Clear to Q
27
ns
High to Low Level Output
t
WQ(Min)
Minimum Width of Pulse
AorBtoQ
200
ns
at Output Q
t
W(out)
Output Pulse Width
A or B to Q
4
5
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
3
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
4
Physical Dimensions
inches (millimeters)
16-Lead Small Outline Molded Package
Order Number DM74LS123M
NS Package Number M16A
5
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