Texas Instruments SN74AHCT123AD

Overview

SN74AHCT123AD from Texas Instruments is a dual retriggerable monostable multivibrator IC in 16-pin SOIC (D) package, operating at 4.5–5.5 V, with TTL-compatible inputs, Schmitt-triggered A/B/CLR inputs, and externally programmable pulse duration via R_ext/C_ext. It delivers precise timing control in digital logic systems requiring edge-triggered, glitch-free one-shot pulses - e.g., debouncing mechanical switches or generating fixed-duration strobes in industrial control sequencers.

For engineers reviewing the SN74AHCT123AD datasheet, SN74AHCT123AD pinout, SN74AHCT123AD application, or SN74AHCT123AD equivalent, this page provides verified functional identity, confirmed SOIC-16 pin mapping, real-world timing behavior (including retriggering and CLR override), and validated alternative options for monostable timing circuits where external RC programming and dual independent channels are required.

Technical Context

The SN74AHCT123AD implements two independent positive-logic monostable multivibrators, each triggered by three distinct input combinations: falling edge on A (with B high), rising edge on B (with A low), or rising edge on CLR (with A low and B high). Pulse width is determined solely by external R_ext and C_ext, with no internal timing elements.

Each channel features Schmitt-trigger inputs on A, B, and CLR to reject noise and tolerate slow transitions, and supports retriggering during an active output pulse to extend duration. The CLR input overrides all trigger conditions and can terminate the output pulse early when driven low - a critical capability for fault recovery and dynamic pulse shaping in real-time systems.

Key Specifications

Pinout & Package

SN74AHCT123AD is housed in a 16-pin SOIC (D) package measuring 9.90 mm × 6.00 mm (body: 9.90 mm × 3.90 mm), with 1.27 mm pitch, gull-wing leads, and surface-mount compatibility.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AHCT123AD, SN74AHCT123ADR offers identical performance with modern packaging and active supply status, while 74VHC123M trades Schmitt-trigger robustness for wider voltage range and lower static power - making SN74AHCT123AD optimal for industrial 5-V environments with marginal signal integrity.

Availability

SN74AHCT123AD is available at Aetrix Electronics and suitable for industrial control panels, test equipment interfaces, and legacy 5-V logic upgrades requiring stable component supply and long-term obsolescence management.

Supply support for SN74AHCT123AD 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 specializing in analog, embedded processing, and logic solutions, with decades of heritage in industry-standard logic families.

The SN74AHCT123AD belongs to TI's AHCT logic series - designed specifically for 5-V TTL-to-CMOS interfacing with enhanced noise immunity, speed, and reliability in industrial and automotive-adjacent applications.

FAQ

What is the recommended external timing component range for SN74AHCT123AD?

The SN74AHCT123AD supports R_ext values from 1 kΩ to 100 kΩ and C_ext from 28 pF to 0.1 μF. For example, a 10 kΩ resistor with a 0.01 μF capacitor yields ~100 μs output pulse width. Always connect the capacitor between Cext and GND, and the resistor between Rext/Cext and V_CC. Avoid exceeding 100 kΩ R_ext to maintain timing accuracy and noise immunity.

Can SN74AHCT123AD operate reliably with slow-switching mechanical inputs?

Yes - the SN74AHCT123AD incorporates Schmitt-trigger circuitry on all A, B, and CLR inputs, providing hysteresis that rejects noise and accommodates input transition times up to several microseconds. This makes the SN74AHCT123AD ideal for direct connection to pushbuttons, limit switches, or relay contacts without external filtering components.

Does SN74AHCT123AD support retriggering during an active output pulse?

Yes - the SN74AHCT123AD is explicitly retriggerable: applying a valid trigger (e.g., falling edge on A with B high) during an ongoing output pulse extends the pulse duration from the new trigger edge. Minimum retrigger interval is ~15 ns, and pulse-width variation between channels is typically <±0.5%, ensuring predictable multi-shot timing behavior.

What is the maximum output drive capability of SN74AHCT123AD?

The SN74AHCT123AD delivers ±8 mA per output at V_CC = 5 V, with VOL ≤ 0.44 V and VOH ≥ 3.8 V under load. This allows direct driving of up to 10 LS-TTL inputs or small indicator LEDs (with series resistor). Exceeding ±25 mA per output risks latch-up or parametric shift, so buffer stages are recommended for higher-current loads.

Is SN74AHCT123AD pin-compatible with older 74LS123 or 74HC123 devices?

No - while functionally similar, SN74AHCT123AD has different pin assignments than 74LS123 (e.g., 74LS123 uses separate R/C pins per channel but lacks dedicated CLR inputs). The SN74AHCT123AD pinout is unique to the '123A family and matches SN74AHCT123ADR and SN74AHCT123AN. Always verify pin functions using Table 3-1 in the official datasheet before substitution.