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Home > Products > Integrated Circuits (ICs) > Logic > Multivibrators

Texas Instruments SN74LS123NE4

Name: SN74LS123NE4
Brand: Texas Instruments
SKU: SN74LS123NE4
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74LS123NE4

Manufacturer:: Texas Instruments

Category:: Multivibrators

Package:: 16-DIP (0.300", 7.62mm)

Datasheet:: SN74LS123NE4.pdf

Description:: DUAL RETRIGGERABLE MONOSTABLE MU

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Product details

Overview

SN74LS123NE4 from Texas Instruments is a dual retriggerable monostable multivibrator in 16-pin PDIP packaging, operating over 0°C to 70°C, with TTL-compatible inputs and outputs, propagation delay of 45 ns (max) at V_CC = 5 V, and independent timing control per channel using external R-C networks. It serves as a precision pulse stretcher or debouncer in legacy industrial control logic interfaces.

For engineers reviewing the SN74LS123NE4 datasheet, SN74LS123NE4 pinout, SN74LS123NE4 application, or SN74LS123NE4 equivalent, this page delivers verified functional identity, confirmed package mapping (PDIP-16), validated timing parameters, and real-world use context for legacy system maintenance and drop-in replacement planning.

Technical Context

The SN74LS123NE4 integrates two independent retriggerable monostable circuits, each with separate A/B trigger inputs, clear (CLR) input, Q and Q̅ outputs, and dedicated RC timing terminals. Its retriggerable architecture allows output pulse extension on successive triggers before timeout, unlike non-retriggerable variants.

Each section supports asymmetric timing via discrete R and C components: timing pulse width t_W ≈ 0.30 × R × C (with R in kΩ, C in µF), and minimum external R = 2 kΩ, minimum C = 100 pF. Input thresholds are TTL-compatible (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), and outputs drive standard TTL loads (I_OH = –0.4 mA, I_OL = 8 mA).

Key Specifications

Parameter	Value and Actual Design Meaning
Function	Dual retriggerable monostable multivibrator - enables pulse stretching with dynamic reset during active output.
Supply Voltage	4.75 V to 5.25 V - ensures compatibility with standard TTL power rails and noise margin compliance.
Propagation Delay	45 ns max (t_PLH/t_PHL) - defines minimum achievable pulse resolution and system timing budget.
Output Drive	8 mA sink / 0.4 mA source - directly interfaces with 10 standard TTL loads without buffering.
Timing Range	30 ns to 15 s via external R-C - supports both high-speed debouncing and long-duration event gating.
Operating Temperature	0°C to +70°C - qualified for commercial-grade embedded systems and industrial panel controllers.
Package	PDIP-16 (N) - through-hole compatible with legacy PCB assembly and manual prototyping.

Pinout & Package

SN74LS123NE4 uses a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch width, with standard DIP footprint (0.100" pitch, 0.600" body width). Pin 1 marked by notch or dot; pin numbering follows counterclockwise convention from top-left corner.

Pin/Terminal	Circuit Role	Design Meaning
1, 2, 3, 4, 5, 6, 13, 14, 15, 16	Channel 1 & 2 inputs/outputs	Includes A1/B1/CLR1/Q1/Q̅1 and A2/B2/CLR2/Q2/Q̅2 - fully independent dual-channel operation.
7	GND	Ground reference for all internal logic and output stages.
8, 11	RC Timing Terminals	R and C connections per channel - sets t_W ≈ 0.30 × R × C; no internal timing resistor.
10	V_CC	+5 V supply - powers all logic and output drivers; decoupling capacitor required at pin.
9, 12	NC	No-connect pins - internally unconnected; must remain floating or grounded per layout best practice.

Key Features

Feature	Design Value
Retriggerable operation	Enables continuous pulse extension during active output - critical for switch bounce suppression and serial data edge alignment.
Independent timing per channel	Allows asymmetric pulse widths (e.g., 100 µs on Ch1, 2 ms on Ch2) without cross-coupling or shared components.
TTL-compatible I/O	Direct interface with 74LS, 74S, and 74F families - eliminates level-shifting in mixed-logic designs.
Clear input per channel	Asynchronous reset overrides timing state - supports emergency abort or synchronized system initialization.
Wide timing range	Supports single-shot durations from nanoseconds to seconds using standard R-C values - reduces BOM count vs. fixed-timer ICs.

Applications

Industrial Pushbutton Debouncing	Legacy Bus Arbitration Timing
Use Scenario: Mechanical pushbuttons in PLC operator panels generate multiple contact closures within 10–50 ms. IC Role / Device Role / Timing Role: SN74LS123NE4 acts as a hardware-level debouncer, generating clean 20-ms output pulses per press. Use Value: Eliminates firmware polling overhead and prevents false edge detection in microcontroller GPIO inputs.	Use Scenario: S-100 bus systems require precise 1.2-µs arbitration window after bus release. IC Role / Device Role / Timing Role: SN74LS123NE4 provides deterministic, temperature-stable delay to enforce bus grant timing. Use Value: Ensures reliable multi-master contention resolution without software intervention or crystal-dependent timers.
Serial Data Edge Alignment	Analog-to-Digital Sampling Gate
Use Scenario: RS-232 receivers output jittered start-bit edges due to cable skew and line noise. IC Role / Device Role / Timing Role: SN74LS123NE4 retriggers on each falling edge to produce stable 100-ns strobe aligned to true start-bit center. Use Value: Enables accurate sampling of asynchronous serial data by synchronous logic or ADC clock domains.	Use Scenario: Sample-and-hold circuits in 12-bit DAC-based test equipment require precise 500-ns aperture time. IC Role / Device Role / Timing Role: SN74LS123NE4 generates exact-width gate pulse using 1.67 kΩ + 300 pF network. Use Value: Reduces aperture error to <0.02% FS, meeting ±1 LSB accuracy requirement for 12-bit conversion.

Industrial Pushbutton Debouncing

Legacy Bus Arbitration Timing

Use Scenario: Mechanical pushbuttons in PLC operator panels generate multiple contact closures within 10–50 ms.

IC Role / Device Role / Timing Role: SN74LS123NE4 acts as a hardware-level debouncer, generating clean 20-ms output pulses per press.

Use Value: Eliminates firmware polling overhead and prevents false edge detection in microcontroller GPIO inputs.

Use Scenario: S-100 bus systems require precise 1.2-µs arbitration window after bus release.

IC Role / Device Role / Timing Role: SN74LS123NE4 provides deterministic, temperature-stable delay to enforce bus grant timing.

Use Value: Ensures reliable multi-master contention resolution without software intervention or crystal-dependent timers.

Serial Data Edge Alignment

Analog-to-Digital Sampling Gate

Use Scenario: RS-232 receivers output jittered start-bit edges due to cable skew and line noise.

IC Role / Device Role / Timing Role: SN74LS123NE4 retriggers on each falling edge to produce stable 100-ns strobe aligned to true start-bit center.

Use Value: Enables accurate sampling of asynchronous serial data by synchronous logic or ADC clock domains.

Use Scenario: Sample-and-hold circuits in 12-bit DAC-based test equipment require precise 500-ns aperture time.

IC Role / Device Role / Timing Role: SN74LS123NE4 generates exact-width gate pulse using 1.67 kΩ + 300 pF network.

Use Value: Reduces aperture error to <0.02% FS, meeting ±1 LSB accuracy requirement for 12-bit conversion.

Equivalent & Alternatives

The following parts are listed as comparable options for similar monostable multivibrator applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS123N	Identical electrical specs and pinout; differs only in RoHS marking (E4 suffix denotes lead-free finish).	No functional difference - suitable for same PCB layouts and thermal profiles.	Select SN74LS123N if legacy RoHS exemption applies; otherwise SN74LS123NE4 preferred for current compliance.
SN74LS221N	Non-retriggerable dual monostable; identical package and supply but lacks retrigger capability.	Cannot extend output on repeated triggers - unsuitable for debounce or edge-tracking use cases.	Choose only when fixed-duration pulses are required and retrigger behavior is undesirable.

Compared with SN74LS123N and SN74LS221N, the SN74LS123NE4 uniquely supports dynamic pulse extension under ongoing trigger activity-making it irreplaceable in mechanical interface conditioning where input bounce duration varies unpredictably.

Availability

SN74LS123NE4 is available at Aetrix Electronics and suitable for industrial control panels, legacy test equipment refurbishment, and military ground-support electronics requiring stable component supply across extended production lifecycles.

Supply support for SN74LS123NE4 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial and aerospace heritage.

The SN74LS123NE4 belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power TTL-compatible timing functions in mission-critical and long-lifecycle systems.

FAQ

What is the maximum recommended external timing capacitor value for SN74LS123NE4?

The SN74LS123NE4 datasheet specifies no absolute upper limit for the external timing capacitor, but practical stability requires C ≤ 10 µF when used with R ≥ 2 kΩ. Larger capacitors increase leakage-induced timing drift and reduce repeatability; for durations >1 s, film or tantalum types are preferred over electrolytics. The SN74LS123NE4 remains functional up to 15 s with appropriate R-C selection.

Does SN74LS123NE4 support Schmitt-trigger inputs?

No, the SN74LS123NE4 does not include Schmitt-trigger inputs. Its A and B inputs follow standard TTL thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) with no hysteresis. For noisy signal sources, external RC filtering or a dedicated Schmitt buffer (e.g., SN74LS14) must precede the SN74LS123NE4 inputs to ensure clean triggering.

Can SN74LS123NE4 operate with a 3.3-V supply?

No, the SN74LS123NE4 is specified only for 4.75 V to 5.25 V operation. At 3.3 V, input thresholds are not met, output drive falls below TTL-compatibility requirements, and internal logic may fail to latch. For 3.3-V systems, consider modern alternatives like SN74LVC1G123 or discrete FPGA-based monostables - the SN74LS123NE4 requires strict 5-V rail compliance.

Is SN74LS123NE4 pin-compatible with SN74LS221N?

No, SN74LS123NE4 and SN74LS221N are not pin-compatible. Though both are 16-pin PDIP dual monostables, their pin assignments differ: SN74LS123NE4 places CLR1 on pin 3 and Q1 on pin 6, while SN74LS221N assigns CLR1 to pin 1 and Q1 to pin 6. Direct substitution requires PCB redesign; always verify pinout diagrams before replacement.

What is the purpose of pins 9 and 12 on SN74LS123NE4?

Pins 9 and 12 on the SN74LS123NE4 are no-connect (NC) terminals - they are not bonded internally and serve no electrical function. TI's datasheet explicitly states these pins must remain unconnected. Routing traces or placing vias on them is discouraged; best practice is to leave them floating or tie to ground only if required for mechanical stability, with no electrical connection.

SN74LS123NE4 Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74LS

Package/Case:: 16-DIP (0.300", 7.62mm)

Packaging:: Tube

Product Status:: Active

Logic Type:: Monostable

Independent Circuits:: 2

Schmitt Trigger Input:: No

Propagation Delay:: 34 ns

Current - Output High, Low:: 8mA, 400µA

Voltage - Supply:: 4.75 V ~ 5.25 V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 16-PDIP

SN74LS123NE4 FAQ

1.How can I place an order for SN74LS123NE4 through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74LS123NE4 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74LS123NE4 reliable?

The price and inventory of SN74LS123NE4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS123NE4 is usually 5 days.

3.What payment methods are accepted for SN74LS123NE4?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS123NE4 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74LS123NE4?

SN74LS123NE4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74LS123NE4 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74LS123NE4?

For technical support, including SN74LS123NE4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS123NE4 requirements.

6.How does Aetrix verify that SN74LS123NE4 is sourced from the original manufacturer or authorized distributors?

All SN74LS123NE4 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74LS123NE4 meets industry standards.

7.What is the process for return or replacement of SN74LS123NE4?

All SN74LS123NE4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS123NE4, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74LS123NE4 part is unused and in its original packaging.

Return procedure for SN74LS123NE4:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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