Texas Instruments CD74HC123PWR

Overview

CD74HC123PWR 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, supports edge-triggering on both A (trailing) and B (leading) inputs, features Schmitt-trigger inputs for noise immunity, and delivers output pulse widths adjustable via external RX/CX components - e.g., 45 µs typical with RX = 10 kΩ and CX = 10 nF at VCC = 5V. It is used in debounce circuits, event timing, and programmable delay generators.

For engineers reviewing the CD74HC123PWR datasheet, CD74HC123PWR pinout, CD74HC123PWR application, or CD74HC123PWR equivalent, key selection considerations include its retriggerable behavior, separate reset per monostable, wide temperature range (–55°C to +125°C), TSSOP-16 package compatibility, and HC logic family characteristics including high noise immunity (NIL/NIH = 30% at VCC = 5V).

Technical Context

The CD74HC123PWR implements two independent monostable multivibrators, each with dual trigger inputs (A and B), an active-low reset (R), and complementary Q/Q outputs. Triggering can occur on either edge: A input responds to falling edges, B to rising edges - enabling flexible synchronization with asynchronous signals. The output pulse width tW = 0.45·RX·CX is externally programmable and retriggerable during the active pulse.

Each monostable includes Schmitt-trigger inputs for robust noise rejection, buffered Q/Q outputs capable of driving 10 LSTTL loads, and independent reset control that terminates the output pulse immediately when asserted low. The device uses standard CMOS silicon process and exhibits balanced propagation delays (e.g., 64 ns max tPLH at VCC = 4.5V, CL = 50 pF) and transition times (19 ns max).

Key Specifications

Pinout & Package

CD74HC123PWR is housed in a 16-pin TSSOP (Thin Shrink Small Outline Package) with 0.65 mm pitch, 4.4 mm width, and 1.2 mm max height - optimized for high-density PCB layouts and automated SMT assembly. Pin 1 is located at the top-left corner with a beveled edge marker.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV123AIPWR and CD74HC423M96, the CD74HC123PWR uniquely combines retriggerability, Schmitt-trigger inputs, and 2V–6V operation - making it the only option among the three suitable for robust, voltage-flexible, noise-prone timing applications across automotive and industrial domains.

Availability

CD74HC123PWR is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, and test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HC123PWR 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 and embedded processing technologies, with over 90 years of innovation in precision timing, power management, and logic solutions.

The CD74HC123PWR belongs to TI's legacy HC logic portfolio, engineered for reliability in harsh environments and designed to replace obsolete TTL-based monostables while maintaining pin-compatible upgrade paths and broad voltage interoperability.

FAQ

What is the minimum external capacitor value supported by CD74HC123PWR?

The CD74HC123PWR supports CX = 0 pF as the theoretical minimum, though practical designs use ≥10 pF for stability. The datasheet specifies CX ≥ 0 pF and RX ≥ 5 kΩ; pulse width scales linearly as tW = 0.45·RX·CX at VCC = 5V. For CD74HC123PWR, using CX = 0 pF yields near-zero pulse width - useful for edge detection with immediate reset, but requires careful layout to avoid parasitic capacitance effects.

Can CD74HC123PWR operate reliably at 3.3V supply?

Yes, CD74HC123PWR operates reliably across 2V–6V, including 3.3V nominal systems. At VCC = 3.3V, VIH = 2.31V (min), VIL = 0.99V (max), and propagation delay increases modestly to ~85 ns (max) - all within specification. Its HC logic family ensures full compatibility with 3.3V CMOS and LVTTL interfaces, making CD74HC123PWR suitable for mixed-voltage designs without level shifters.

How does the retriggering behavior of CD74HC123PWR differ from non-retriggerable monostables like CD74HC423?

CD74HC123PWR extends its output pulse width upon each valid trigger (A or B) occurring before the initial timeout completes, whereas CD74HC423 ignores subsequent triggers until the first pulse ends. This makes CD74HC123PWR ideal for measuring burst durations or maintaining enable states during intermittent activity - a functional distinction confirmed in the datasheet's description and truth table. Retriggering is inherent to CD74HC123PWR's architecture and requires no external circuitry.

What is the maximum recommended external resistor value for CD74HC123PWR timing networks?

The datasheet does not specify an absolute maximum RX, but practical limits arise from leakage current and noise sensitivity. For stable operation at –55°C to +125°C, TI recommends RX ≤ 1 MΩ to maintain timing accuracy and avoid excessive sensitivity to stray capacitance or input leakage (II ≤ ±1 µA). With CX = 10 nF, RX = 1 MΩ yields tW ≈ 4.5 ms - well within usable range. Higher values risk timing drift; CD74HC123PWR's design assumes RX in the 5 kΩ–100 kΩ range for optimal performance.

Does CD74HC123PWR require external pull-up or pull-down resistors on unused inputs?

Yes - per the datasheet, all unused inputs (A, B, R) on either monostable must be terminated high or low to prevent floating nodes, which could cause increased ICC, erratic triggering, or latch-up. For CD74HC123PWR in TSSOP-16, this means connecting unused A/B/R pins to VCC or GND via ≤10 kΩ resistors. Leaving them unconnected violates absolute maximum ratings and compromises reliability, especially across the full –55°C to +125°C operating range.