Nexperia USA Inc. 74HCT123DB,118

Overview

74HCT123DB,118 from Nexperia is a dual retriggerable monostable multivibrator with independent reset inputs, TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 5.0 V), 16-pin SO16 package (SOT109-1), and programmable pulse width via external REXT/CEXT networks. It delivers precise timing control in digital logic systems requiring extended or dynamically adjustable output pulses - e.g., debouncing mechanical switches in industrial HMI panels.

For engineers reviewing the 74HCT123DB,118 datasheet, 74HCT123DB,118 pinout, 74HCT123DB,118 application, or 74HCT123DB,118 equivalent, key selection criteria include TTL-level input compatibility, retriggerable pulse extension capability, direct asynchronous reset functionality, Schmitt-triggered A/B inputs for noise immunity, and guaranteed operation from -40 °C to +125 °C.

Technical Context

This device implements two independent monostable circuits, each with dual edge-triggered inputs (nA: negative-edge, nB: positive-edge), a dedicated active-low reset (nRD), and complementary outputs (nQ HIGH / nQ LOW). Pulse width tW is set externally by REXT and CEXT, with typical values ranging from 75 ns (REXT = 5 kΩ, CEXT = 0 pF) up to 450 μs (REXT = 10 kΩ, CEXT = 100 nF).

Retriggering extends the output pulse on successive valid edges at nA or nB before timeout; reset terminates it immediately. Schmitt-trigger action on nA/nB inputs ensures robust operation with slow-rising/falling signals, while clamp diodes enable interfacing to voltages beyond VCC using current-limiting resistors.

Key Specifications

Pinout & Package

74HCT123DB,118 uses the SO16 plastic small outline package (SOT109-1), 16-pin, 3.9 mm body width, with gull-wing leads and pin 1 index marker. Thermal resistance θJA = 110 K/W (JEDEC Std 51-2).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC123DB,118 and SN74LV123ADBR, the 74HCT123DB,118 uniquely bridges legacy TTL signal levels and modern 5 V industrial power domains while maintaining full -40 °C to +125 °C qualification - making it optimal for retrofitting or brownfield equipment upgrades.

Availability

74HCT123DB,118 is available at Aetrix Electronics and suitable for industrial switch debounce, serial data pulse stretching, motor run-time limiting, and power sequencing delay applications requiring stable component supply across extended temperature ranges.

Supply support for 74HCT123DB,118 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 delivering high-performance, reliable discrete, logic, and MOSFET devices optimized for efficiency, miniaturization, and robustness in high-volume applications.

The 74HCT123 series belongs to Nexperia's industry-standard logic portfolio, designed specifically for timing-critical digital systems requiring retriggerable pulse generation, noise-immune triggering, and seamless integration with legacy TTL infrastructure.

FAQ

What is the maximum recommended value for REXT to ensure stable operation?

The datasheet specifies REXT up to 1000 kΩ at VCC = 5.0 V. However, stability degrades above 500 kΩ due to leakage current effects and parasitic capacitance. For reliable 100 ms+ pulse widths, use REXT ≤ 470 kΩ with CEXT ≥ 220 nF and verify with oscilloscope measurement under worst-case temperature and supply conditions.

Can 74HCT123DB,118 drive an LED directly?

Yes - each output can sink or source up to 4 mA. With VCC = 5 V and a 1 kΩ current-limiting resistor, the device delivers ~4 mA through a standard red LED (VF ≈ 1.8 V), producing visible illumination. For higher brightness or multiple LEDs, add a transistor buffer to avoid exceeding IO absolute maximum ratings.

How does the reset input (nRD) interact with ongoing retriggering?

An active-low nRD pulse immediately forces nQ = LOW and nQ = HIGH, terminating any active or extended pulse regardless of retrigger activity. The monostable remains in reset until nRD returns HIGH, after which it resumes normal operation only upon next valid trigger edge - no race condition or metastability occurs.

Is external capacitor CEXT required for basic functionality?

No - the device operates with CEXT = 0 pF, yielding minimum pulse width (~75 ns at VCC = 5 V). However, CEXT is mandatory for programmable timing: omitting it disables adjustable pulse generation. Always connect CEXT from nCEXT to GND and place it close to the IC to minimize noise coupling and trace inductance.