NXP Semiconductors 74HC123D/AUJ

Overview

74HC123D/AUJ from Nexperia is a dual retriggerable monostable multivibrator with independent reset inputs, designed for precise pulse generation and timing control in digital systems. It operates from 2.0 V to 6.0 V, delivers propagation delays as low as 19 ns (VCC = 6.0 V), supports external timing components (REXT up to 1000 kΩ, CEXT up to 100 nF), and features Schmitt-trigger inputs for noise immunity - used in debounce circuits, event stretching, and programmable delay generators.

For engineers reviewing the 74HC123D/AUJ datasheet, 74HC123D/AUJ pinout, 74HC123D/AUJ application, or 74HC123D/AUJ equivalent, key selection considerations include its dual independent monostable architecture, retriggerable pulse extension capability, direct active-low reset per channel, SO16 package compatibility, and CMOS-level input thresholds enabling interoperability with mixed-voltage logic families.

Technical Context

The 74HC123D/AUJ implements two fully independent monostable multivibrators sharing only VCC and GND. Each channel uses edge-triggered inputs (nA: negative-edge, nB: positive-edge) with Schmitt-trigger action, allowing robust operation with slow-rising signals. Pulse width is externally set via REXT and CEXT on pins nREXT/CEXT and nCEXT, with typical tW ranging from 75 ns (REXT = 5 kΩ, CEXT = 0 pF) to 450 μs (REXT = 10 kΩ, CEXT = 100 nF).

Each monostable supports real-time pulse extension via retriggering before timeout and immediate termination via LOW-going edge on dedicated nRD. Input clamping diodes permit interface to voltages exceeding VCC when current-limiting resistors are used, and latch-up immunity exceeds 100 mA per JESD78 Class II Level B.

Key Specifications

Pinout & Package

74HC123D/AUJ is housed in a plastic small outline package (SO16, SOT109-1) with 16 leads, 3.9 mm body width, and standard 1.27 mm lead pitch - compatible with automated PCB assembly and legacy footprint designs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT123D and SN74LV123ADR, the 74HC123D/AUJ uniquely balances wide supply voltage (2–6 V), robust noise immunity (Schmitt inputs), and proven industrial temperature qualification (-40 °C to +125 °C), making it optimal for mixed-voltage embedded control where reliability outweighs marginal speed gains.

Availability

74HC123D/AUJ is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, and consumer appliance control systems requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for 74HC123D/AUJ 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

Nexperia is a global semiconductor expert focused on essential efficiency technologies, delivering high-performance logic, analog, and discrete components with industry-leading quality and reliability.

The 74HC123D/AUJ belongs to Nexperia's 74HC logic family, engineered for low-power, high-noise-immunity digital timing applications in harsh environments - emphasizing robustness, wide operating margins, and seamless integration with microcontrollers and sensors.

FAQ

What is the maximum external timing capacitor value supported by the 74HC123D/AUJ?

The 74HC123D/AUJ supports external timing capacitors up to 100 nF, as validated in the datasheet's dynamic characteristics table (tW = 450 μs at CEXT = 100 nF, REXT = 10 kΩ). Larger values increase pulse width but reduce timing accuracy due to leakage and parasitic effects; for CEXT > 10 nF, the formula tW = K × REXT × CEXT applies, with K = 0.45 at VCC = 5.0 V.

Does the 74HC123D/AUJ require external pull-up or pull-down resistors on its trigger inputs?

No, the 74HC123D/AUJ does not require external pull-up or pull-down resistors on its 1A, 1B, 2A, or 2B inputs because they feature built-in Schmitt-trigger action with defined hysteresis. However, unused inputs must be tied to VCC or GND to prevent floating states; the datasheet explicitly recommends grounding pins 1CEXT and 2CEXT to minimize noise coupling into the timing network.

Can the 74HC123D/AUJ operate reliably at 3.3 V supply voltage?

Yes, the 74HC123D/AUJ is fully specified for operation at 3.3 V (within its 2.0 V to 6.0 V range). At VCC = 3.3 V, VIH = ~2.3 V and VIL = ~1.0 V (interpolated from datasheet curves), ensuring compatibility with 3.3 V microcontrollers and FPGAs. Propagation delay increases to ~35 ns (typ.), and output drive remains ±25 mA - sufficient for most 3.3 V logic interfacing.

How does the retrigger time (trtrig) of the 74HC123D/AUJ depend on external components?

The retrigger time trtrig of the 74HC123D/AUJ depends directly on REXT and CEXT values: for VCC = 5.0 V and CEXT > 10 pF, trtrig = 30 + 0.19 × REXT × CEXT⁰·⁹ + 13 × REXT¹·⁰⁵ (ns). This ensures the monostable only extends its output pulse when trigger edges are spaced farther apart than trtrig - preventing unintended extension from high-frequency noise or jitter.

Is the 74HC123D/AUJ pin-compatible with the 74LS123?

No, the 74HC123D/AUJ is not pin-compatible with the 74LS123. While both are dual monostables, the 74LS123 uses different pin assignments (e.g., LS123 has separate R and C pins per channel, no Schmitt inputs, and TTL thresholds). The 74HC123D/AUJ follows the industry-standard 74HC123 pinout defined in SOT109-1, which differs electrically and physically from the older 74LS123 DIP-16 layout.