Texas Instruments CD74HC123NS

Overview

CD74HC123NS from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, operating from 2V to 6V, featuring Schmitt-trigger inputs on both A and B trigger lines, buffered Q/Q̅ outputs, and external RC timing (t_W = 0.45·R_XC_X at V_CC = 5V) for pulse widths from nanoseconds to milliseconds. It supports edge-triggering (A = trailing, B = leading), overriding reset termination, and functions across -55°C to +125°C in industrial and aerospace timing applications.

For engineers reviewing the CD74HC123NS datasheet, CD74HC123NS pinout, CD74HC123NS application, or CD74HC123NS equivalent, this page delivers verified timing parameters, SOP-16 package details, dual-monostable functional behavior, reset-controlled pulse extension/termination logic, and direct alternatives for retriggerable one-shot designs requiring wide temperature range and CMOS-level noise immunity.

Technical Context

The CD74HC123NS implements two independent retriggerable monostable circuits, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Triggering initiates a precise output pulse whose width is determined solely by external R_X and C_X, with no dependence on input rise/fall times due to integrated Schmitt triggers.

Each monostable supports pulse extension via retriggering before timeout and immediate termination via LOW on R. The Q and Q̅ outputs are fully buffered, enabling fanout of 10 LSTTL loads over full temperature range, and propagation delays (e.g., 64 ns max A→Q at V_CC = 4.5V, T_A = 125°C) are tightly matched between channels within ±2%.

Key Specifications

Pinout & Package

CD74HC123NS is housed in a 16-pin Small Outline Package (SOP), 300 mil body width, with standard 0.050" lead pitch and JEDEC MO-153-compliant footprint. Thermal resistance θ_JA = 64°C/W enables reliable operation up to 125°C ambient without forced airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC423NSR and SN74LV123ANSR, the CD74HC123NS uniquely supports retriggerable pulse extension while maintaining full -55°C to +125°C operation and 2–6V supply compatibility - making it optimal for adaptive timing in harsh-environment embedded controllers.

Availability

CD74HC123NS is available at Aetrix Electronics and suitable for industrial motor control, automotive powertrain timing, and avionics watchdog systems requiring stable component supply across extreme temperature ranges and long production lifecycles.

Supply support for CD74HC123NS 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, embedded processing, and logic solutions for industrial, automotive, and aerospace markets.

The CD74HC123NS belongs to TI's legacy HC logic family, designed specifically for robust, RC-programmable timing in mission-critical systems where predictable pulse generation, wide temperature resilience, and noise-immune triggering are mandatory.

FAQ

What is the minimum external resistor value for stable operation of the CD74HC123NS?

The CD74HC123NS specifies a minimum external timing resistor R_X of 5 kΩ for reliable monostable operation across its full temperature and voltage range. Using lower values may cause timing inaccuracies or failure to trigger due to excessive current draw into the internal timing node. Always verify R_X ≥ 5 kΩ and C_X ≥ 0 pF per the datasheet's absolute maximum ratings table.

Can the CD74HC123NS generate asymmetric pulse widths on Q and Q̅ outputs?

No, the CD74HC123NS produces strictly complementary Q and Q̅ outputs with identical pulse widths and matched propagation delays. The datasheet confirms pulse width match between circuits in the same package is ±2% under identical R_X/C_X conditions. Any observed asymmetry indicates external loading imbalance or measurement error-not an inherent feature of the CD74HC123NS.

Does the CD74HC123NS support simultaneous triggering of both monostables?

Yes, the CD74HC123NS allows independent or simultaneous triggering of both monostables using their dedicated A/B/R inputs. Each channel operates autonomously: triggering Mono 1 does not affect Mono 2 timing or state. This enables synchronized dual-pulse generation (e.g., for complementary PWM dead-time) or independent event timing in the same package.

What is the maximum recommended external capacitor value for the CD74HC123NS?

The CD74HC123NS datasheet does not specify a maximum C_X value, but practical limits arise from leakage current and timing accuracy. For stable operation beyond 100 ms pulse widths, use low-leakage capacitors (e.g., polypropylene or C0G ceramic) and verify performance at -55°C and +125°C. At V_CC = 5V, t_W = 0.45·R_XC_X remains valid up to ~100 µF with R_X = 100 kΩ, though leakage may dominate at larger values.

Is the CD74HC123NS pin-compatible with the CD74HCT123NSR?

Yes, the CD74HC123NS and CD74HCT123NSR share identical SOP-16 pinouts and terminal functions. However, they differ electrically: CD74HC123NS operates from 2–6V with CMOS input thresholds, while CD74HCT123NSR requires 4.5–5.5V and accepts standard TTL input levels (V_IL ≤ 0.8V, V_IH ≥ 2.0V). Swapping them requires verifying supply voltage and input driver compatibility.