Texas Instruments SN74LV123AD

Overview

SN74LV123AD from Texas Instruments is a dual retriggerable monostable multivibrator IC with Schmitt-trigger inputs, designed for 2-V to 5.5-V operation. It generates precise, programmable output pulses (e.g., 90–110 µs at C_ext = 0.01 µF, R_ext = 10 kΩ) with maximum 11 ns propagation delay at 5 V, and supports edge-triggered operation via A/B/CLR inputs in AV receivers, Blu-ray players, and embedded PCs.

For engineers reviewing the SN74LV123AD datasheet, SN74LV123AD pinout, SN74LV123AD application, or SN74LV123AD equivalent, key selection considerations include its retriggerable pulse generation up to 100% duty cycle, I_off-enabled partial-power-down capability, mixed-mode voltage tolerance on all ports, and guaranteed glitch-free power-up reset behavior.

Technical Context

The SN74LV123AD implements two independent monostable multivibrators, each using external R_ext/C_ext networks to set output pulse duration (t_w = K × R_ext × C_ext, where K ≈ 1.0 for C_ext ≥ 1000 pF). Triggering is configurable for rising-edge (A=H, B=L), falling-edge (A=L, B=H), or gated logic (A=L, B=H, CLR↑), with Schmitt-trigger hysteresis on all control inputs enabling robust operation with slow/noisy signals.

Each channel features complementary Q and Q̅ outputs, overriding clear (CLR) that terminates pulses early, and I_off circuitry that disables outputs during power-down to prevent backflow current. The device maintains consistent timing across –40°C to 125°C and supports mixed-voltage interfacing between 2.3-V and 5.5-V domains without level shifters.

Key Specifications

Pinout & Package

SN74LV123AD is housed in a 16-pin SOIC package (6.00 mm × 9.90 mm body size), optimized for automated assembly and thermal performance (R_θJA = 73°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC123A and CD74HC123M, the SN74LV123AD uniquely combines I_off-enabled power-down safety, Schmitt-triggered CLR for noise immunity, and guaranteed 11-ns max delay - making it optimal for modern low-voltage, mixed-signal embedded timing applications.

Availability

SN74LV123AD is available at Aetrix Electronics and suitable for AV receivers, Blu-ray players, and embedded PCs requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for SN74LV123AD 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 solutions, with decades of expertise in logic IC design and manufacturing.

The SN74LV123AD belongs to TI's LV family of low-voltage logic devices, engineered for robust operation across wide supply ranges (2 V–5.5 V) and demanding industrial, consumer, and computing applications.

FAQ

What is the minimum external capacitance required for stable operation of the SN74LV123AD?

The SN74LV123AD does not specify a minimum external capacitance value; however, timing accuracy degrades below 100 pF due to parasitic effects. For reliable pulse duration control, use C_ext ≥ 100 pF with appropriate R_ext scaling. At C_ext = 28 pF and R_ext = 2 kΩ, typical t_w is 200–240 ns - verified in TI's SCLS393Q datasheet Section 7.10. Always minimize trace length to C_ext and R_ext/C_ext pins to preserve timing integrity in the SN74LV123AD.

How does the SN74LV123AD handle power-up sequencing in multi-rail systems?

The SN74LV123AD guarantees glitch-free power-up: Q outputs initialize low and Q̅ outputs high regardless of V_CC ramp rate, eliminating need for external reset circuits. This behavior is intrinsic to the device architecture and confirmed across –40°C to 125°C in TI's SCLS393Q datasheet Section 9.1. When used alongside other ICs in multi-rail systems, the SN74LV123AD stabilizes before most MCUs complete boot - simplifying system-level timing design.

Can the SN74LV123AD generate asymmetric pulse widths on its two channels simultaneously?

Yes - the SN74LV123AD supports independent pulse width programming per channel via separate R_ext/C_ext networks. Channel 1 uses pins 14 (1Cext) and 15 (1Rext/Cext); Channel 2 uses pins 6 (2Cext) and 7 (2Rext/Cext). With distinct RC values (e.g., 10 kΩ/100 pF for Channel 1, 22 kΩ/47 pF for Channel 2), the SN74LV123AD delivers precisely different t_w values - validated in timing tables Sections 7.9–7.11 of the official datasheet.

What is the maximum recommended R_ext value for the SN74LV123AD to maintain timing accuracy?

Texas Instruments specifies R_ext ≤ 1 MΩ in the SN74LV123AD datasheet (Section 7.3) to ensure stable charging of C_ext and avoid leakage-induced timing drift. At R_ext = 1 MΩ and C_ext = 100 pF, t_w ≈ 100 µs (K ≈ 1.0); exceeding 1 MΩ increases sensitivity to temperature, voltage, and process variation. For long-duration pulses (>1 ms), use lower R_ext with larger C_ext - e.g., 10 kΩ/100 nF - to retain accuracy in the SN74LV123AD.

Does the SN74LV123AD support true bidirectional triggering (both rising and falling edges on the same input pin)?

No - the SN74LV123AD requires dedicated inputs for edge polarity: 1A/2A for falling-edge triggers (when corresponding B is low) and 1B/2B for rising-edge triggers (when corresponding A is high). It does not combine both edges on one pin. However, the dual-channel architecture allows simultaneous rising-edge detection on Channel 1 (via 1B) and falling-edge detection on Channel 2 (via 2A), enabling flexible event capture in systems like digital video cameras - as documented in the SN74LV123AD function table (Section 9.4).