Texas Instruments CD74HC423E

Overview

CD74HC423E from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, designed for precise pulse generation and timing control in digital systems. It features Schmitt-trigger inputs on both A and B trigger pins, buffered Q and Q̅ outputs, 2V–6V operation, -55°C to +125°C temperature range, and external RC-controlled pulse widths down to ~40 µs (RX = 10 kΩ, CX = 10 nF).

For engineers reviewing the CD74HC423E datasheet, CD74HC423E pinout, CD74HC423E application, or CD74HC423E equivalent, this device supports edge-triggered timing functions where pulse width accuracy, retriggerability, reset override, and wide supply voltage tolerance are critical - especially in industrial control, instrumentation, and legacy TTL/CMOS interface circuits.

Technical Context

The CD74HC423E implements two independent monostable multivibrators, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Unlike the '123 family, the '423 variant does not support negative-to-positive reset pulses - its reset is strictly active-low level-sensitive. Pulse width t_W = 0.45 × R_XC_X at V_CC = 5 V, with minimum R_X = 5 kΩ and C_X ≥ 0 pF.

Each monostable provides Q and Q̅ buffered outputs with balanced propagation delay (e.g., 64 ns max t_PLH/t_PHL at V_CC = 4.5 V, CL = 50 pF) and transition times (≤22 ns). Input hysteresis ensures noise immunity, and fanout supports up to 10 LSTTL loads over full temperature range.

Key Specifications

Pinout & Package

CD74HC423E is housed in a 16-lead plastic dual in-line package (PDIP-N), with 0.3-inch body width and standard through-hole footprint. Pin spacing is 0.1 inch (2.54 mm), and lead pitch matches JEDEC MS-001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC123E and SN74LV123A, the CD74HC423E uniquely balances wide supply range (2–6 V), robust Schmitt-trigger inputs, and level-sensitive reset - making it the preferred choice for industrial timing where reliability across voltage and noise conditions outweighs edge-triggered reset flexibility or sub-20 ns speed.

Availability

CD74HC423E is available at Aetrix Electronics and suitable for industrial control, test equipment, and legacy system interface applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC423E 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 delivering analog and embedded processing solutions, with decades of expertise in logic, timing, and interface ICs.

The CD74HC423E belongs to TI's HC-series high-speed CMOS logic family, engineered for drop-in compatibility with TTL while delivering lower power, wider voltage operation, and enhanced noise immunity in demanding industrial and aerospace applications.

FAQ

What is the key functional difference between CD74HC423E and CD74HC123E?

The CD74HC423E uses level-sensitive active-low reset (R pin), whereas CD74HC123E supports both level-sensitive and negative-to-positive edge-triggered reset. This makes CD74HC423E simpler to drive with standard logic gates but less flexible for open-drain reset sources. Both share identical pinout, timing equations, and electrical specifications otherwise.

Can CD74HC423E operate reliably at 3.3 V supply?

Yes, CD74HC423E operates across 2 V to 6 V, including 3.3 V. At 3.3 V, typical output pulse width remains calculable via t_W ≈ 0.45·R_XC_X, and propagation delay increases modestly (e.g., ~85 ns max vs. 64 ns at 4.5 V). All DC specs - including VIH/VIL thresholds and fanout - are guaranteed across the full voltage range.

How do I calculate the output pulse width for CD74HC423E?

Use t_W = 0.45 × R_X × C_X, where R_X is in ohms and C_X is in farads, yielding t_W in seconds. For example, R_X = 10 kΩ and C_X = 10 nF gives t_W ≈ 45 µs at V_CC = 5 V. The coefficient varies slightly with V_CC; see Figure 5 in the CD74HC423E datasheet for K-factor correction.

Does CD74HC423E require external pull-up or pull-down resistors on unused inputs?

Yes - all unused inputs (1A, 1B, 1R, 2A, 2B, 2R) must be terminated either HIGH or LOW. Floating inputs risk increased supply current, erratic triggering, or latch-up. TI recommends tying unused A/B inputs to V_CC or GND via ≤10 kΩ resistors; reset inputs should be pulled HIGH (inactive) unless actively driven.

Is CD74HC423E RoHS compliant and lead-free?

Yes, CD74HC423E is RoHS compliant and features NiPdAu (NIPDAU) lead finish. Per TI's packaging addendum, it carries "Yes" in the RoHS column, uses lead-free terminations, and is rated for standard reflow profiles. The PDIP package has no MSL rating (N/A), reflecting its through-hole construction and exemption from moisture sensitivity requirements.