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DM74LS123 Dual Retriggerable One-Shot with Clear and Complementary Outputs
August 1986 Revised April 2000
DM74LS123 Dual Retriggerable One-Shot with Clear and Complementary Outputs
General Description
The DM74LS123 is a dual retriggerable monostable multivibrator 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 activeHIGH transition trigger input. The clear (CLR) input terminates the output 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 ( ). To obtain the best trouble free operation from this device please read the operating rules as well as the Fairchild Semiconductor one-shot application notes carefully and observe recommendations.
Features
s DC triggered from active-HIGH transition or active-LOW transition inputs s Retriggerable to 100% duty cycle s Compensated for VCC and temperature variations s Triggerable from CLEAR input s DTL, TTL compatible s Input clamp diodes
Ordering Code:
Order Number DM74LS123M DM74LS123SJ DM74LS123N Package Number M16A M16D N16E Package Description 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow 16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide 16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter "X" to the ordering code.
Connection Diagram
Function Table
Inputs CLEAR L X X H H A X H X L L B X X L H H Q L L Outputs Q H H
H = HIGH Logic Level L = LOW Logic Level X = Can Be Either LOW or HIGH = Positive Going Transition = Negative Going Transition = A Positive Pulse = A Negative Pulse

L

H

(c) 2000 Fairchild Semiconductor Corporation
DS006386
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DM74LS123
Functional Description
The basic output pulse width is determined by selection of an external resistor (RX) and capacitor (CX). 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. Retriggering 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.
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 constants high-grade mica, glass, polypropylene, polycarbonate, or polystyrene material capacitors may be used. For large time constants use tantalum or special aluminum capacitors. If the timing capacitors have leakages approaching 100 nA or if stray capacitance from either terminal 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 prevent high inverse leakage current. This switching diode is not needed for the DM74LS123 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 DM74LS123 the negative terminal of the capacitor should be connected to the "CEXT" pin of the device (Figure 1). FIGURE 2. 5. For CX < 1000 pF see Figure 3 for tW vs. CX family curves with RX as a parameter:
FIGURE 3. FIGURE 1. 3. For CX >> 1000 pF the output pulse width (tW) is defined as follows: tW = KRX CX where [RX is in k] [CX is in pF] [tW is in ns] K 0.37 4. The multiplicative factor K is plotted as a function of CX below for design considerations: FIGURE 4.
"Rremote" should be as close to the device pin as possible.
6. To obtain variable pulse widths by remote trimming, the following circuit is recommended:
7. The retriggerable pulse width is calculated as shown below: T = tW + tPLH = K x RX x CX + tPLH The retriggered pulse width is equal to the pulse width plus a delay time period (Figure 5).
FIGURE 5.
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DM74LS123
Operating Rules (Continued) 8. Output pulse width variation versus VCC and temperatures: Figure 6 depicts the relationship between pulse width variation versus VCC, and Figure 7 depicts pulse width variation versus temperatures.
9. Under any operating condition CX and RX must be kept as close to the one-shot device pins as possible to minimize 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 from 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. 10. 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.
FIGURE 6.
11. VCC and ground wiring should conform to good highfrequency standards and practices so that switching transients on the VCC and ground return leads do not cause interaction between one-shots. A 0.01 F to 0.10 F bypass capacitor (disk ceramic or monolithic type) from VCC to ground is necessary on each device. Furthermore, the bypass capacitor should be located as close to the VCC-pin as space permits.
Note: For further detailed device characteristics and output performance please refer to the Fairchild Semiconductor one-shot application note AN-372.
FIGURE 7.
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DM74LS123
Absolute Maximum Ratings(Note 1)
Supply Voltage Input Voltage Operating Free Air Temperature Range Storage Temperature 7V 7V 0C to +70C -65C to +150C
Note 1: The "Absolute Maximum Ratings" are those values beyond which the safety of the device cannot be guaranteed. The device should not be operated at these limits. The parametric values defined in the Electrical Characteristics tables are not guaranteed at the absolute maximum ratings. The "Recommended Operating Conditions" table will define the conditions for actual device operation.
Recommended Operating Conditions
Symbol VCC VIH VIL IOH IOL tW Supply Voltage HIGH Level Input Voltage LOW Level Input Voltage HIGH Level Output Current LOW Level Output Current Pulse Width (Note 2) REXT CEXT CWIRE TA External Timing Resistor External Timing Capacitance Wiring Capacitance at REXT/CEXT Terminal Free Air Operating Temperature 0 A or B HIGH A or B LOW Clear LOW 40 40 40 5 No Restriction 50 70 260 k F pF C ns Parameter Min 4.75 2 0.8 -0.4 8 Nom 5 Max 5.25 Units V V V mA mA
Note 2: TA = 25C and V CC = 5V.
Electrical Characteristics
over recommended operating free air temperature range (unless otherwise noted) Symbol VI VOH VOL Parameter Input Clamp Voltage HIGH Level Output Voltage LOW Level Output Voltage II IIH IIL IOS ICC Input Current @ Max Input Voltage HIGH Level Input Current LOW Level Input Current Short Circuit Output Current Supply Current Conditions VCC = Min, II = -18 mA VCC = Min, IOH = Max VIL = Max, VIH = Min VCC = Min, IOL = Max VIL = Max, VIH = Min IOL = 4 mA, VCC = Min VCC = Max, VI = 7V VCC = Max, VI = 2.7V VCC = Max, VI = 0.4V VCC = Max (Note 4) VCC = Max (Note 5)(Note 6)(Note 7) -20 12 2.7 3.4 0.35 0.25 0.5 0.4 0.1 20 -0.4 -100 20 mA A mA mA mA Min Typ (Note 3) Max -1.5 Units V V
V
Note 3: All typicals are at VCC = 5V, TA = 25C. Note 4: Not more than one output should be shorted at a time, and the duration should not exceed one second. Note 5: Quiescent ICC is measured (after clearing) with 2.4V applied to all clear and A inputs, B inputs grounded, all outputs OPEN, CEXT = 0.02 F, and REXT = 25 k. Note 6: ICC 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 F, and REXT = 25 k. Note 7: 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.
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DM74LS123
Switching Characteristics
at VCC = 5V and TA = 25C RL = 2 k Symbol Parameters From (Input) To (Output) tPLH tPLH Propagation Delay Time LOW-to-HIGH Level Output Propagation Delay Time LOW-to-HIGH Level Output tPHL Propagation Delay Time HIGH-to-LOW Level Output tPHL Propagation Delay Time HIGH-to-LOW Level Output tPLH tPHL tWQ(Min) tW(out) Propagation Delay Time LOW-to-HIGH Level Output Propagation Delay Time HIGH-to-LOW Level Output Minimum Width of Pulse at Output Q Output Pulse Width CL = 15pF CEXT = 0 pF, REXT = 5 k Min A to Q B to Q Max 33 44 CL = 15pF CEXT = 1000 pF, REXT = 10 k Min Max ns ns Units
A to Q
45
ns
B to Q
56
ns
Clear to Q Clear to Q A or B to Q A or B to Q
45 27 200 4 5
ns ns ns s
5
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DM74LS123
Physical Dimensions inches (millimeters) unless otherwise noted
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow Package Number M16A
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DM74LS123
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide Package Number M16D
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DM74LS123 Dual Retriggerable One-Shot with Clear and Complementary Outputs
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide Package Number N16E
Fairchild does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and Fairchild reserves the right at any time without notice to change said circuitry and specifications. LIFE SUPPORT POLICY FAIRCHILD'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. www.fairchildsemi.com 8 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com

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