Texas Instruments CD74HC123PWT

Overview

CD74HC123PWT from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, designed for precise pulse generation and timing control in digital systems. It operates from 2V to 6V, features Schmitt-trigger inputs on both A and B trigger pins, supports output pulse widths from nanoseconds to milliseconds via external RX/CX, and delivers buffered Q and Q outputs with ±25mA drive capability.

For engineers reviewing the CD74HC123PWT datasheet, CD74HC123PWT pinout, CD74HC123PWT application, or CD74HC123PWT equivalent, this device is selected for edge-triggered timing circuits requiring wide temperature operation (–55°C to +125°C), retriggerable one-shot behavior, reset-override functionality, and compatibility with LSTTL/CMOS logic families.

Technical Context

The CD74HC123PWT implements two independent monostable circuits, each with separate A (trailing-edge) and B (leading-edge) trigger inputs, individual reset (R) pins, and complementary Q/Q outputs. Timing is externally controlled by resistor RX and capacitor CX, with pulse width calculated as t_W = 0.45 × R_XC_X at V_CC = 5V.

Each monostable supports retriggering during an active output pulse, enabling pulse extension, and allows immediate termination of the output pulse via a LOW on its dedicated reset input. Input thresholds are defined by CMOS-compatible VIH/VIL levels, and propagation delays (e.g., 64 ns max A→Q at V_CC = 4.5V, CL = 50pF) are tightly specified across the full temperature range.

Key Specifications

Pinout & Package

TSSOP-16 package (PW), 4.4 mm × 5.0 mm × 1.2 mm body height, 0.65 mm pitch, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC423M96 and SN74LVC1G123DCKR, the CD74HC123PWT uniquely delivers dual retriggerable monostables with per-channel reset and edge-selectable inputs in a 16-pin TSSOP - making it the only option for compact, flexible, and safety-aware multi-timing architectures.

Availability

CD74HC123PWT is available at Aetrix Electronics and suitable for industrial control panels, aerospace avionics interfaces, and automotive engine management systems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC123PWT 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 for industrial, automotive, and communications markets.

The CD74HC123PWT belongs to TI's legacy HC logic family, engineered for robust, low-power, wide-temperature digital timing functions in mission-critical systems where reliability and parameter stability outweigh raw speed.

FAQ

What is the minimum external capacitor value supported by the CD74HC123PWT?

The CD74HC123PWT supports CX = 0 pF as the minimum external capacitance value. With CX = 0 and RX ≥ 5 kΩ, the device achieves minimal pulse widths governed by internal propagation delays - typically ~64 ns at V_CC = 4.5V. This enables sub-microsecond timing resolution when paired with appropriate resistor values and load conditions.

Can the CD74HC123PWT operate reliably at 3.3V supply voltage?

Yes, the CD74HC123PWT is fully specified for operation from 2V to 6V, including 3.3V nominal systems. At V_CC = 3.3V, input thresholds scale proportionally (VIH ≈ 2.3V, VIL ≈ 1.0V), and propagation delays increase modestly versus 5V operation - all parameters remain guaranteed across –55°C to +125°C per the datasheet's HC-type specifications.

How does the retriggering behavior of the CD74HC123PWT differ from non-retriggerable monostables like the CD74HC423?

The CD74HC123PWT extends its current output pulse upon receiving a new trigger (A or B) before the original pulse completes, whereas the CD74HC423 ignores subsequent triggers until the output returns to quiescent state. This makes the CD74HC123PWT ideal for applications requiring adaptive timing windows - such as watchdog extensions or gated clock stretching - where pulse duration must dynamically respond to input activity.

Is the CD74HC123PWT pin-compatible with other packages in the same family, such as CD74HC123M96?

Yes, the CD74HC123PWT (TSSOP-16) shares identical pin numbering, function mapping, and electrical specifications with CD74HC123M96 (SOIC-16) and CD74HC123E (PDIP-16). All variants use the same 16-pin layout per the functional diagram in the datasheet, enabling drop-in replacement across packages when board layout and thermal constraints permit.

What is the purpose of the Schmitt-trigger inputs on the CD74HC123PWT A and B pins?

The Schmitt-trigger inputs on the CD74HC123PWT A and B pins provide hysteresis (typically 30% of V_CC) to reject noise and ensure clean, bounce-free triggering from slow or noisy signals - such as mechanical switches, sensor outputs, or long PCB traces. This eliminates external RC filtering or comparator circuits, simplifying design and improving timing predictability in electrically harsh environments.