Texas Instruments SN74LS123DG4

Overview

SN74LS123DG4 from Texas Instruments is a dual retriggerable monostable multivibrator IC used for precise pulse generation, timing control, and event debouncing in TTL-compatible digital systems. It features two independent monostable circuits, 16-pin SOIC packaging, guaranteed propagation delay of 45 ns (max) at VCC = 5 V, output drive capability of 8 mA sink / 0.4 mA source, and operates over 0°C to 70°C ambient temperature.

For engineers reviewing the SN74LS123DG4 datasheet, SN74LS123DG4 pinout, SN74LS123DG4 application, or SN74LS123DG4 equivalent, this page delivers verified functional identity, confirmed SOIC-16 pin mapping, real-world timing behavior, and validated drop-in alternatives for legacy TTL timing design and industrial control upgrades.

Technical Context

The SN74LS123DG4 implements two identical, edge-triggered monostable multivibrators with independent A/B inputs, clear (CLR) control, and Q/Q̅ complementary outputs per channel. Each circuit supports both positive- and negative-edge triggering via separate input configurations and allows external RC timing network adjustment across a wide range (10 ns to 10 s).

It uses standard TTL logic levels (VIH = 2.0 V min, VIL = 0.8 V max), maintains compatibility with 74LS family voltage thresholds and noise margins, and includes internal Schmitt-trigger inputs on the B inputs to suppress noise-induced false triggers during slow signal transitions.

Key Specifications

Pinout & Package

SN74LS123DG4 is housed in a 16-pin Small Outline Integrated Circuit (SOIC) package with 1.27 mm pitch, gull-wing leads, and JEDEC MS-012AB compliance. The package is RoHS-compliant with NiPdAu lead finish and rated for moisture sensitivity Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS123DG4, SN74LS123DR offers identical performance in automated SMT production, while SN74LS123N provides direct pin-compatible through-hole replacement-both preserve full retriggerable monostable functionality without circuit redesign.

Availability

SN74LS123DG4 is available at Aetrix Electronics and suitable for industrial control timing, keyboard debounce circuits, serial data pulse stretching, and legacy bus arbitration logic requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS123DG4 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 ICs with broad industrial, automotive, and communications portfolio coverage.

The SN74LS123DG4 belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power TTL-compatible timing functions in cost-sensitive, reliability-critical industrial and instrumentation systems.

FAQ

What is the primary function of the SN74LS123DG4?

The SN74LS123DG4 is a dual retriggerable monostable multivibrator that generates precise, externally adjustable output pulses in response to input triggers. Each of its two independent channels accepts edge-triggered inputs (A and B), supports Schmitt-trigger noise immunity on B inputs, and produces complementary Q and Q̅ outputs. Its retriggerable architecture allows new triggers to extend or restart an active pulse - making it ideal for debouncing, pulse shaping, and timing window generation in TTL-based systems. The SN74LS123DG4 retains full compatibility with 74LS logic voltage thresholds and drive capabilities.

Does the SN74LS123DG4 require external timing components?

Yes, the SN74LS123DG4 requires external resistors and capacitors to set pulse width for each channel. Pins 8 and 9 connect to R_EXT1 and C_EXT1 for Channel 1; pins 11 and 12 connect to R_EXT2 and C_EXT2 for Channel 2. Pulse width t_W is approximately 0.3 × R × C (minimum) to 0.5 × R × C (typical), enabling ranges from ~10 ns to 10 s. No internal timing elements exist - all timing is determined solely by these external components. The SN74LS123DG4 does not operate without them.

Is the SN74LS123DG4 pin-compatible with other 74LS123 variants?

Yes, the SN74LS123DG4 is pin-compatible with all 16-pin 74LS123 variants in SOIC (D), PDIP (N), and SSOP (DB) packages - including SN74LS123DR, SN74LS123N, and SN74LS123DBR. All share identical pin numbering, signal assignments, and electrical interface definitions. Differences lie only in package type, packaging format (tube vs. tape-and-reel), and surface finish - not in pinout or logic behavior. The SN74LS123DG4 can replace any of these in a SOIC-16 footprint without modification.

What is the maximum operating frequency or minimum pulse width supported by the SN74LS123DG4?

The SN74LS123DG4 supports minimum output pulse widths down to 10 ns (typical) when using small external RC values - limited primarily by propagation delay (45 ns max) and rise/fall times (~15 ns). There is no specified maximum operating frequency, as it is not a clocked device; instead, its usable trigger rate depends on the configured pulse width and retriggering behavior. For reliable retriggering, successive triggers must occur after t_W begins but before it completes. The SN74LS123DG4 achieves stable sub-100 ns pulse generation with appropriate R/C selection and layout.

Can the SN74LS123DG4 be used in place of the SN74LS122?

No, the SN74LS123DG4 is not a functional replacement for the SN74LS122. While both are dual monostables, the SN74LS122 is non-retriggerable and has different input structure (single trigger input per channel, no B input), distinct timing equations, and incompatible pinout - especially for clear and output terminals. The SN74LS123DG4's retriggerable behavior, Schmitt-trigger B inputs, and independent clear lines provide capabilities the SN74LS122 lacks. Substituting SN74LS123DG4 for SN74LS122 would require circuit redesign and cannot be done as a drop-in replacement.