Texas Instruments SN74LS122DR

Overview

SN74LS122DR from Texas Instruments is a retriggerable monostable multivibrator IC in a 14-pin SOIC package, operating over 0°C to 70°C, with typical propagation delay of 25 ns at V_CC = 5 V and load capacitance ≤ 15 pF, used for pulse shaping and timing control in digital logic systems.

For engineers reviewing the SN74LS122DR datasheet, SN74LS122DR pinout, SN74LS122DR application, or SN74LS122DR equivalent, this device supports precise one-shot generation with retriggering capability, TTL-compatible inputs, and guaranteed output pulse width stability across temperature and supply voltage variations.

Technical Context

The SN74LS122DR implements dual independent retriggerable monostable multivibrators in a single IC, each with separate A and B trigger inputs, Q and Q̅ outputs, and a common reset (R̅) input. Its internal Schmitt-trigger input structure enables noise immunity on asynchronous triggers.

Timing is resistor-capacitor (RC) programmable per channel: pulse width t_W ≈ 0.3 × R × C, where R ranges from 2 kΩ to 40 kΩ and C from 100 pF to 10 µF. Output drive capability is ±8 mA at V_CC = 5 V, compatible with standard TTL loads.

Key Specifications

Pinout & Package

SN74LS122DR is housed in a 14-pin Small Outline Integrated Circuit (SOIC) package (D package), 3.90 mm wide, 8.65 mm long, 1.75 mm max height, with 1.27 mm lead pitch and gull-wing leads. 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 SN74LS122DR, SN74LS123DR offers deterministic single-shot timing but no retriggering, while 74HC123DR delivers lower power and higher speed at the cost of TTL-level compatibility-making SN74LS122DR uniquely suited for legacy retriggerable timing in 5-V TTL environments.

Availability

SN74LS122DR is available at Aetrix Electronics and suitable for industrial control panels, test equipment design, and legacy system maintenance requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS122DR 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 U.S.-based semiconductor company founded in 1930, specializing in analog and embedded processing technologies with broad industrial, automotive, and consumer product portfolios.

The SN74LS122DR belongs to TI's legacy 74LS logic family, designed specifically for robust, low-cost timing and waveform generation in commercial-grade digital systems requiring TTL compatibility and retriggerable behavior.

FAQ

What is the maximum recommended timing capacitor value for SN74LS122DR?

The SN74LS122DR datasheet specifies a maximum external timing capacitor value of 10 µF for stable operation. Larger values may cause timing inaccuracies due to leakage current and internal comparator offset effects. For pulse widths exceeding 30 seconds, consider cascading or using microcontroller-based timing instead of extending C beyond 10 µF. Always use low-leakage dielectric types such as polyester or polypropylene for best accuracy in SN74LS122DR applications.

Can SN74LS122DR operate with a 3.3-V supply?

No, SN74LS122DR is specified only for 4.75 V to 5.25 V operation and is not guaranteed to function correctly at 3.3 V. Its internal TTL-compatible input thresholds and output drive characteristics depend on nominal 5-V rail conditions. Attempting 3.3-V operation risks undefined logic states, reduced noise margin, and failure to meet propagation delay or pulse width specifications. Use 74HC123 or 74LVC123 for 3.3-V compatible monostable functionality instead of SN74LS122DR.

How does the retriggerable feature of SN74LS122DR differ from SN74LS123DR?

SN74LS122DR allows new trigger events to restart the output pulse while it is still active-extending its duration dynamically. In contrast, SN74LS123DR ignores subsequent triggers during an ongoing output pulse and only responds to the next trigger after the output returns low. This makes SN74LS122DR ideal for applications like switch debouncing where rapid successive actuations must extend the output window, whereas SN74LS123DR suits applications needing strict one-pulse-per-trigger behavior.

What is the minimum external timing resistor value for SN74LS122DR?

The minimum recommended external timing resistor for SN74LS122DR is 2 kΩ. Lower values increase current draw through the internal timing circuit and may degrade pulse width accuracy or cause excessive power dissipation in the IC. At 2 kΩ and 100 pF, SN74LS122DR achieves a nominal pulse width of ~60 ns-close to its practical lower limit. Always verify timing with oscilloscope measurement in final SN74LS122DR circuit implementation.

Is SN74LS122DR pin-compatible with other 74LS-series monostables?

SN74LS122DR is pin-compatible with SN74LS122N (PDIP-14) and SN74LS122NSR (SOP-14) in the same 14-pin configuration, sharing identical pin functions and electrical characteristics. However, it is not pin-compatible with 16-pin variants like SN74LS123DR or SN74123N due to differing channel count, trigger architecture, and pin assignments. Always confirm package footprint and pin mapping before substituting SN74LS122DR in existing layouts.