Texas Instruments SN74LS423NSR

Overview

SN74LS423NSR from Texas Instruments is a dual monostable multivibrator IC in 16-pin SOP (NS) package, featuring independent trigger inputs, reset control, and complementary Q/Q̅ outputs per channel. It operates over 0°C to 70°C, supports TTL-compatible input thresholds, and delivers typical output propagation delay of 35 ns at V_CC = 5 V. It is used in pulse shaping, timing control, and debouncing circuits in industrial logic systems.

For engineers reviewing the SN74LS423NSR datasheet, SN74LS423NSR pinout, SN74LS423NSR application, or SN74LS423NSR equivalent, key selection criteria include its dual independent monostable architecture, non-retriggerable mode operation, 16-pin SOP thermal and mounting compatibility, and guaranteed TTL-level DC specifications across commercial temperature range.

Technical Context

The SN74LS423NSR implements two identical, non-retriggerable monostable multivibrators with separate A/B trigger inputs, R reset inputs, and Q/Q̅ outputs per section. Each section uses internal resistor-capacitor timing networks (externally adjustable via R_EXT and C_EXT) to generate precise one-shot pulses with duration t_W = 0.30 × R_EXT(kΩ) × C_EXT(µF).

It features TTL-compatible input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), guaranteed fan-out of 20 LS-TTL loads, and output drive capability of I_OH = –0.4 mA / I_OL = 8 mA at V_CC = 5 V. The device requires no external clock and operates asynchronously on edge-triggered inputs.

Key Specifications

Pinout & Package

SOP-16 (NS) package: 16-pin small-outline plastic package with 1.27 mm lead pitch, 10.4 mm body width, 5.4 mm body depth, and maximum height of 2.00 mm. RoHS-compliant, NIPDAU lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS123DR and CD74HC221M, the SN74LS423NSR offers native TTL drive strength and guaranteed commercial-temperature stability without external level shifters, making it optimal for legacy 5-V logic upgrades where pinout and timing behavior must remain unchanged.

Availability

SN74LS423NSR is available at Aetrix Electronics and suitable for industrial control timing, keyboard debouncing, pulse width modulation prep, and legacy system glue logic requiring stable component supply and long-term manufacturability.

Supply support for SN74LS423NSR 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 company headquartered in Dallas, Texas, delivering analog, embedded processing, and logic products for industrial, automotive, and communications markets.

The SN74LS423NSR belongs to TI's legacy 74LS logic family, designed specifically for robust, low-cost, TTL-compatible timing and control functions in commercial-grade digital systems.

FAQ

What is the timing accuracy tolerance of the SN74LS423NSR over temperature?

The SN74LS423NSR exhibits ±15% timing variation over its full operating range (0°C to +70°C) due to R/C component drift and internal process variation. This tolerance applies to the nominal t_W = 0.30 × R_EXT × C_EXT calculation. For tighter accuracy, use 1% metal-film resistors and NP0/C0G capacitors. The SN74LS423NSR datasheet specifies this variation under "Timing Characteristics" with test conditions at V_CC = 5 V and T_A = 25°C.

Can the SN74LS423NSR operate with a single timing network shared between both sections?

No-the SN74LS423NSR requires independent R_EXT and C_EXT networks for each monostable section (Pins 6/7 and 14/15). Sharing components causes cross-coupling and unpredictable pulse widths. Each section has dedicated timing pins to ensure isolation. The SN74LS423NSR does not support common timing; attempting shared R/C will result in incorrect or unstable output behavior.

Is the SN74LS423NSR pin-compatible with the SN74LS423N or SN74LS423D?

Yes-the SN74LS423NSR shares identical pinout and electrical functionality with SN74LS423N (PDIP-16) and SN74LS423D (SOIC-16). All three use the same 16-pin dual-in-line footprint mapping, including identical A/B/R/Q/Q̅/R_EXT/C_EXT/GND/V_CC assignments. The SN74LS423NSR replaces them in tape-and-reel SOP packaging while maintaining full functional equivalence.

Does the SN74LS423NSR support retriggerable operation?

No-the SN74LS423NSR is strictly non-retriggerable. Once triggered, a new A-input transition during the timing interval has no effect until the current pulse completes. This behavior is inherent to its internal architecture and confirmed in the SN74LS423NSR functional description. For retriggerable operation, TI recommends SN74LS123 or SN74LS221 instead.

What is the maximum recommended value for R_EXT in the SN74LS423NSR?

The SN74LS423NSR datasheet specifies R_EXT up to 40 kΩ for reliable operation. Values above this may cause timing instability or failure to trigger due to insufficient charging current into the internal timing node. At 40 kΩ and 10 µF, t_W ≈ 120 ms-well within the 18 s max. Exceeding 40 kΩ risks marginal performance; the SN74LS423NSR design assumes R_EXT ≤ 40 kΩ for guaranteed specification compliance.