Texas Instruments SN74LS123NSR

Overview

SN74LS123NSR from Texas Instruments is a dual retriggerable monostable multivibrator in a 16-pin SOP (NS) package, operating from 4.75 V to 5.25 V with typical propagation delay of 25 ns at V_CC = 5 V and C_EXT = 10 nF, R_EXT = 10 kΩ. It provides precise, edge-triggered one-shot timing for pulse shaping and debouncing in industrial control logic and legacy TTL systems.

For engineers reviewing the SN74LS123NSR datasheet, SN74LS123NSR pinout, SN74LS123NSR application, or SN74LS123NSR equivalent, this page delivers verified functional identity, confirmed SOP-16 pin mapping, temperature-rated performance (0 °C to 70 °C), RoHS-compliant NIPDAU lead finish, and validated alternatives for TTL-compatible monostable timing replacement.

Technical Context

The SN74LS123NSR implements two independent retriggerable monostable circuits, each with separate A and B trigger inputs (active-low and active-high), reset (R̅), Q and Q̅ outputs, and external RC timing networks. Each section supports both negative- and positive-edge triggering via complementary input pairs.

Timing duration is set externally by R_EXT and C_EXT, with output pulse width t_W ≈ 0.33 × R_EXT × C_EXT (for R_EXT ≥ 2 kΩ, C_EXT ≥ 100 pF). The device maintains LS-TTL compatibility: input thresholds match standard TTL, output drive capability is ±8 mA at V_OL ≤ 0.5 V / V_OH ≥ 2.7 V.

Key Specifications

Pinout & Package

SOP (NS) package: 16-pin surface-mount, 1.27 mm pitch, 10.4 mm × 5.4 mm body, 2.00 mm max height, RoHS-compliant NIPDAU finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS123DR, SN74LS123NSR offers identical functionality in SOP-16 for compatibility with narrower trace spacing, while SN74LS221D trades retriggerability for marginally faster timing - making SN74LS123NSR the sole choice for edge-sensitive, self-extending pulse generation.

Availability

SN74LS123NSR is available at Aetrix Electronics and suitable for industrial control timing, keyboard debouncing, legacy system glitch suppression, and test equipment pulse generation requiring stable component supply across long-lifecycle embedded programs.

Supply support for SN74LS123NSR 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 founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and consumer design support.

The SN74LS123NSR belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power TTL-compatible timing functions in cost-sensitive, reliability-critical industrial and instrumentation systems.

FAQ

What is the maximum recommended value for R_EXT in SN74LS123NSR timing networks?

The SN74LS123NSR datasheet specifies R_EXT ≤ 40 kΩ for stable operation. Values above this limit increase susceptibility to leakage-induced timing drift and reduced noise immunity. For durations beyond 30 s, consider digital alternatives - the SN74LS123NSR is optimized for sub-second precision timing, not long-interval counting.

Does SN74LS123NSR support 3.3 V logic interfacing?

No. SN74LS123NSR is strictly a 5 V TTL device: its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and output levels (V_OH ≥ 2.7 V at 5 V) are incompatible with 3.3 V CMOS logic families. Direct connection risks undriven inputs or excessive current into 3.3 V receivers. Use level translators or select 74LVC-series monostables for mixed-voltage systems.

Can SN74LS123NSR operate with ceramic capacitors below 100 pF?

No. The SN74LS123NSR requires C_EXT ≥ 100 pF for reliable timing accuracy and stability. Smaller values cause increased sensitivity to stray capacitance and process variation, leading to inconsistent pulse widths. For sub-100 ns timing, use dedicated high-speed comparators or FPGA-based solutions instead of the SN74LS123NSR.

Is SN74LS123NSR pin-compatible with SN74LS123N (PDIP-16)?

Yes. SN74LS123NSR (SOP-16) and SN74LS123N (PDIP-16) share identical pin numbering, function assignment, and electrical specifications. Only the package type differs - allowing direct substitution in existing layouts where SOP footprint is supported, or requiring adapter boards for through-hole prototyping.

What is the purpose of the Q̅ output on SN74LS123NSR?

The Q̅ output on SN74LS123NSR provides the logical inverse of the Q output for each monostable section. This eliminates the need for external inverters when both true and complement timing signals are required - such as driving differential clock enables or complementary transistor switches in power control circuits using the SN74LS123NSR.