Texas Instruments CD74HC123ME4

Overview

CD74HC123ME4 from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, Schmitt-trigger inputs on both A and B trigger lines, buffered Q and Q̅ outputs, and external RC timing control (t_W = 0.45·R_XC_X at V_CC = 5 V). It operates from 2 V to 6 V, supports -55°C to +125°C industrial/military temperature range, and delivers precise pulse-width generation for timing-critical digital systems.

For engineers reviewing the CD74HC123ME4 datasheet, CD74HC123ME4 pinout, CD74HC123ME4 application, or CD74HC123ME4 equivalent, this device is selected for edge-triggered pulse stretching, reset-terminated timing windows, and dual independent one-shot functions in noise-prone environments requiring high noise immunity (NIL/NIH = 30% of V_CC).

Technical Context

The CD74HC123ME4 implements two independent CMOS monostable multivibrators, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Triggering is enabled by Schmitt-trigger inputs, ensuring robust operation against slow-rising or noisy signals. Retriggering extends the output pulse width without requiring full timeout - critical for variable-duration event capture.

Timing is externally set via R_X and C_X, with minimum R_X = 5 kΩ and C_X = 0 pF. Pulse width accuracy depends on V_CC and temperature, with typical t_W = 45 µs (R_X = 10 kΩ, C_X = 10 nF, V_CC = 5 V). Propagation delays are balanced (t_PLH/t_PHL matched within ±10 ns at 5 V), supporting deterministic timing in synchronous logic interfaces.

Key Specifications

Pinout & Package

CD74HC123ME4 is housed in a 16-pin SOIC (D) package, 7.5 mm × 10.3 mm body, 1.75 mm height, with 1.27 mm pitch. Pin 1 marked by beveled corner or notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC423E and SN74LV123ADR, the CD74HC123ME4 uniquely combines retriggerability, Schmitt-trigger inputs, and -55°C to +125°C operation - making it the only choice for robust, field-deployable timing in harsh environments where pulse extension and noise resilience are mandatory.

Availability

CD74HC123ME4 is available at Aetrix Electronics and suitable for industrial motor control, automotive sensor interfacing, test equipment signal generation, and military communications timing requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC123ME4 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 ICs, with decades of heritage in high-reliability timing and interface solutions.

The CD74HC123ME4 belongs to TI's HC logic family - designed for low-power, high-noise-immunity digital timing applications where precision, temperature stability, and interoperability with legacy TTL and modern CMOS systems are essential.

FAQ

What is the minimum external capacitor value supported by the CD74HC123ME4?

The CD74HC123ME4 supports C_X = 0 pF as the minimum external capacitance value. Timing relies on the RC network formed by R_X and C_X, and with C_X = 0, the device still produces a defined minimum pulse width determined by internal parasitic capacitance and R_X. This enables ultra-short pulse generation down to ~100 ns when R_X is minimized to 5 kΩ.

Can the CD74HC123ME4 operate reliably at 2.5 V supply voltage?

Yes, the CD74HC123ME4 is fully specified for operation from 2 V to 6 V, including 2.5 V. At 2.5 V, parameters such as propagation delay increase (t_PLH/t_PHL ≤ 375 ns), input thresholds scale proportionally (VIH ≈ 1.5 V, VIL ≈ 0.5 V), and noise immunity remains at 30% of V_CC. All DC and switching specifications in the datasheet apply across this full range.

How does the reset function interact with an ongoing output pulse on the CD74HC123ME4?

Applying a LOW to either R pin (1R or 2R) immediately forces the corresponding Q output LOW and Q̅ HIGH, terminating the active output pulse regardless of remaining timing interval. The reset is asynchronous and overrides all trigger activity - once released (R returns HIGH), the monostable remains in quiescent state until next valid A or B edge. This behavior is confirmed in the Truth Table and Figure 1 of the CD74HC123ME4 datasheet.

Is the CD74HC123ME4 pin-compatible with the CD74HCT123M series?

Yes, the CD74HC123ME4 shares identical 16-pin SOIC (D) package footprint and pinout with CD74HCT123M variants. However, they differ electrically: CD74HC123ME4 accepts 2–6 V supplies and has CMOS-input thresholds, while CD74HCT123M requires 4.5–5.5 V and features TTL-compatible inputs (VIH = 2 V min, VIL = 0.8 V max). Direct substitution requires matching supply and input logic levels.

What is the maximum recommended value for R_X when using the CD74HC123ME4?

The CD74HC123ME4 datasheet does not specify a maximum R_X value, but practical limits arise from leakage current and timing accuracy. For reliable operation across -55°C to +125°C, R_X should not exceed 1 MΩ - higher values increase sensitivity to PCB leakage and stray capacitance, degrading pulse width consistency. TI application notes recommend R_X ≤ 500 kΩ for production designs requiring ±5% timing tolerance.