DM74LS123N ,7 V, dual retriggerable one-shot with clear and complementary outputNational
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DM74LS123M-DM74LS123N
7 V, dual retriggerable one-shot with clear and complementary output
National
Semiconductor
DM74LS123 Dual Retriggerable One-Shot
with Clear and Complementary Outputs
General Description
The DM74LS123 is a dual retriggerable monostabie 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 (Rf). 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.
Features
a DC triggered from active-high transition or active-Iow
transition inputs
l: Fietriggerable to 100% duty cycle
I: Compensated tor Vcc and temperature variations
" Triggerable from CLEAR input
I: DTI., TTL compatible
I: Input clamp diodes
Functional Description
The basic output pulse width is determined by selection of
an external resistor (Rx) and capacitor (Ox). Once triggered.
the basic pulse width may be extended by rsstriggedng the
gated active-Iow transition or active-high transition inputs or
be reduced by use of the active-Iow 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 "O'' output.
Connection Diagram
DuaI-ln-Llne Package
CEXT Can
Vcc t21 62 cm2 " A2
Ire I15 I14 Its I12 I11 I10 ft
D 0 cm
I1 2 a
'4 Is Is " 8
A1 BI cut ii, Q2 CEXT REXT/ GND
TL/Ft6M6-1
Order Number DM74LS123M or DM74LS123N
See NS Package Number M16A or N16E
Function Table
Inputs Outputs
CLEAR A B o 5
L x x L H
x H x L H
x x L L H
H L t .11 Ir
H I H -CL Tr
t L H .n. U
H = High Logic Level
L a Low Logic Level
X = Can Be Either Low or High
t = Positive Going Transition
l = Negative Going Transition
J% = A Positive Pulse
Ir = A Negative Pulse
SZLS'I
Absolute Maximum Ratings (Note)
If Mllltary/Aerospace speemed devices are required,
please contact the National Semiconductor Sales
Offlce/Dlstrlbutors for avallablllty and tspeelfittatlons.
Supply Voltage 7V
Input Voltage 7V
Note: The "Absolute Maximum Ratings" are those values
beyond which the safety of the device cannot be guaran-
teed. The device should not be operated at these limits. The
parametric values defined in the "Electrical Characteristics"
table are not guaranteed at the absolute maximum ratings.
The "Recommended Operating Conditions " table will define
Operating Free Air Temperature Range
Storage Temperature
WC to + 70''C
-65'C to +150“C
Recommended Operating Conditions
the conditions for actual device operation.
Symbol Parameter Mln Nom Max Units
Vcc Supply Voltage 4.75 5 5.25 V
vm High Level Input Voltage 2 V
" Low Level Input Voltage 0.8 V
IOH High Level Output Current - 0.4 mA
kx. Low Level Output Current 3 mA
tw Pulse Width A or B High 40
(Note 6) A or B Low 40 ns
Clear Low 40
REXT External Timing Resistor 5 260 kn
CEXT External Timing Capacitance No Restriction "
Cme Wiring Capacitance ' 50 pF
at REXT/CEXT Terminal
TA Free Air Operating Temperature 0 70 'C
Electrical Characteristics over recommended operating free air temperature range (unless otherwise noted)
Symbol Parameter Condltlons Min (N3: 1) Max Unlts
VI lnputClamp Voltage Vcc = Min, II = -18 mA --1.5 V
VOH High Level Output VCC = Min, lor, = Max 2.7 3.4 V
Voltage " = Max, VIH = Min
VOL Low Level Output Vcc = Min, lor. = Mex th35 0.5
Voltage " = Max, " = Min V
kx = 4 mA, Vcc = Min 0.25 0.4
II Esumt 833:3; tt Max Vcc Max, VI 7V 0.1 m A
IIH High Level InputCurrent Vcc = Max,V| = 2.7V 20 pA
In Low Level Input Current Vcc = Max, VI = 0.4V -0.4 mA
los itfir,tfigih'lnt tgc 2)Max -20 - 100 mA
'60 Supply Current Vcc = Max (Notes 3,4 and 5) 12 20 mA
Not. 1: All typicals are at Vcc = w, TA = 25’C.
Note 2.. Not more than one output should be shorted at a time, and the duratiun should not exceed one second.
Note 3: Quiescent log is measured (after clearing) with A4V applied to all clear and A inputs. B inputs grounded, all outputs open, CEXT = 0.02 'SF, and
REXT = 25 kn.
Note 4: Ice is measured in the triggered state with 2.4V applied to all clear and B inputs, A inputs grounded, all outputs open, CEXT = 0.02 pF, and REXT = 25 kn.
Note 6: With all outputs open and 4.5V applied to all data and clear inputs, 'cc is measured alter a momentary ground, then 4.5V is applied to the clock.
Note ti.. TA = 25''C and Vcc = 5V.
Switching Characteristics at Vcc = 5V and TA == 25'C
nL=2kn
Symbol Parameters $33231? CExr = ti, Je', = 5 m CEXT = Jg Ji,21', = 10 Kn Unns
Mln Max Mln Max
tPt.H 'lr,',',',",?,'));)?,,'',,?,]'',',,'', Moo as ns
1.... 'lr,elr,tiigltthThig'ut Btot2 44 ns
tPHL r'2,1'e1e1t,','hTl"trut Atol5 as ns
tPHL 'r't1'e1tl,11il,thTlCut BtoO 56 ns
tpt.H [e,','li,1tiig1tth'l,'C,t aemrtoCa 45 ns
tPHL (.',rC'1',1t':fl,tht'tt, Cleartot2 27 ns
tWQtMin) 21:33:31 llidth of Pulse A or B to Q 200 ns
tMom) Output Pulse Width A or B to Q 4 5 PS
Operating Rules
1. An external resistor (Rx) and an external capacitor (Cx)
are required for proper operation. The value of Cx 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 Cx 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.
3. For Cx >> 1000 pF the output pulse width (T w) is de-
fined as follows:
Tw = KRx Cx
where [Fix is in kn]
tCx is in pF]
[Tw is in ns]
K 2rd 0.37
4. The multiplicative factor K is plotted as a function of Cx
below for design considerations:
" " vm-snv
0.1 us
" tif "
0 .2 .I , I 1.01.21.11j
'W' COEFFICIENT
TLIF/8386-2
FIGURE 1
Operating Rules (Continued)
5. For Cx < 1000 pF see Figure 2 for Tw vs Cx family
curves with Fix as a parameter:
ttts n-z-m:
Vcc-5.0V
10 too 1000
cm in“
TL/F/6386-3
FIGURE 2
6. To obtain variable pulse widths by remote trimming, the
following circuit is recommended:
PIN RX
m 03 tttit Ctr'-.".'
- h Hm
HN Cl'"" 11:1.
(6) on (m ht
TUF/6386-4
FIGURE 3
Note: "Rremms" should be as close to the device pin as possible.
7. The retriggerabie pulse width is calculated as shown be-
T=--Tw+tPLH--=KxRxxCx+tpcH
The retriggered pulse width is equal to the pulse width
plus a delay time period (Figure 4).
Fl |__|
F-T------"
OUTPUT __l L
TL/F/6386-5
FIGURE 4
8. Output pulse width variation versus Vcc and tempera-
tures: Figure 5 depicts the relationship between pulse
width variation versus Jar, and Figure 6 depicts pulse
width variation versus temperatures.
IO , I
Cm- 1000 "
5 __T|-25'C
I " 5 " 5
m: (V)
TL/F/8386-6
FIGURE 5
Hm-‘IDK
Ctn-IDOOpF
5 - Vcc=5.DV
ose w,,..,..,,'''''" N
-60-30 0 30 60 90120150
AMBiENT TEMPERATURE Ptl)
TL/F/6388-7
FIGURE 6
9. Under any operating condition Cx and Rx 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 Cx 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 trom the appropriate equations. A
non-inductive and low capacitive path is necessary to
ensure complete discharge of Cx in each cycle of its
operation so that the output pulse width will be accurate.
IO, The CEXT 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 . V00 and ground wiring should conform to good high-tre-
quency standards and practices so that switching tran-
sients on the V00 and ground return leads do not cause
interaction between one-shots. A 0.01 p.F to 0.10 p.F
bypass capacitor (disk ceramic or monolithic type) from
VCC to ground is necessary on each device. Further.
more, the bypass capacitor should be located as close
to the Vcc-pin as space permits.
For further detailed device MtttratttttrUtltm and output performance
please rotor to the NSC one-shot application note M4436.
This datasheet has been :
www.ic-phoenix.com
Datasheets for electronic components.
National Semiconductor was acquired by Texas Instruments.
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This file is the datasheet for the following electronic components:
DM74LS123N - product/dm74ls123n?HQS=TI-nu|I-nu|l-dscataIog-df-pf-null-wwe
DM74LS123M - product/dm74ls123m?HQS=T|-nu|I-nu|I-dscataIog-df-pf-null-wwe
