Texas Instruments SN74LS122NSR

Overview

SN74LS122NSR from Texas Instruments is a retriggerable monostable multivibrator IC in SOP-14 package, operating over 0°C to 70°C, with typical propagation delay of 25 ns at V_CC = 5 V and output drive capability of ±8 mA. It features two independent monostable circuits, each with separate A/B trigger inputs, reset (R̅), and Q/Q̅ outputs, used for pulse shaping, debouncing, and timing control in legacy TTL systems.

For engineers reviewing the SN74LS122NSR datasheet, SN74LS122NSR pinout, SN74LS122NSR application, or SN74LS122NSR equivalent, this page delivers verified functional identity, confirmed SOP-14 pin mapping, temperature-rated performance data, and validated drop-in alternatives for industrial control, instrumentation, and retro-compatibility designs.

Technical Context

The SN74LS122NSR implements dual retriggerable monostables using bipolar TTL logic, where each section accepts negative-edge triggers on A and B inputs and supports asynchronous reset via active-low R̅. Timing is set externally by R-C networks connected to C_EXT and R_EXT pins, enabling adjustable output pulse widths from ~20 ns to seconds.

It maintains LS-TTL compatibility: input thresholds match standard TTL (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), output levels meet V_OL ≤ 0.5 V at 8 mA sink and V_OH ≥ 2.7 V at 0.4 mA source, and it draws I_CC ≈ 19 mA max at 5 V - optimized for low-power legacy system integration without level-shifting.

Key Specifications

Pinout & Package

SOP-14 (NS) package: 14-pin small-outline plastic package, 1.27 mm lead pitch, 8.1 mm × 10.4 mm body size, 2.00 mm max height, gull-wing leads, pin 1 marked by beveled corner or index area.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS122N and SN74LS123DR, the SN74LS122NSR provides SOP-14 surface-mount compatibility without sacrificing timing fidelity or retriggering behavior - making it optimal for volume-manufactured legacy-system replacements where footprint and thermal profile matter.

Availability

SN74LS122NSR is available at Aetrix Electronics and suitable for industrial control logic, legacy system timing, instrumentation signal conditioning, and test equipment pulse generation requiring stable component supply across long-lifecycle programs.

Supply support for SN74LS122NSR 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, embedded processing, and logic ICs with broad industrial and automotive qualification.

The SN74LS122NSR belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-power TTL-compatible timing functions in cost-sensitive, long-lifecycle industrial and instrumentation applications.

FAQ

What is the maximum recommended external timing capacitor value for SN74LS122NSR?

The SN74LS122NSR datasheet specifies no absolute upper limit, but practical stability and leakage constraints recommend keeping C_EXT ≤ 10 µF. Larger values increase sensitivity to capacitor leakage and stray capacitance, potentially causing pulse width drift or failure to trigger reliably - especially at elevated temperatures. For stable operation beyond 100 ms, use film or tantalum capacitors with low leakage and verify with actual board-level testing.

Can SN74LS122NSR operate with a 3.3 V supply?

No. The SN74LS122NSR is strictly a 5 V TTL device: its internal bipolar transistor structure requires V_CC = 4.75–5.25 V for guaranteed logic thresholds, propagation delay, and output drive. Operation at 3.3 V results in undefined outputs, excessive propagation delay (>100 ns), and potential latch-up - it is not 3.3 V tolerant and must be powered from a regulated 5 V rail.

Is SN74LS122NSR pin-compatible with SN74LS123 series devices?

No. Although both are dual retriggerable monostables, SN74LS122NSR uses SOP-14 with dedicated A/B/R̅/C/Q/Q̅ pins per section, while SN74LS123 variants use SOP-16 or SOIC-16 with different pin assignments (e.g., separate clear inputs and shared timing resistors). No PCB-level compatibility exists - direct substitution requires schematic and layout revision.

What is the minimum pulse width achievable with SN74LS122NSR?

The SN74LS122NSR achieves a minimum pulse width of approximately 20 ns under typical conditions (V_CC = 5 V, T_A = 25°C), limited by internal propagation delays and external R-C network parasitics. Using low-capacitance ceramic capacitors (<10 pF) and short traces, sub-30 ns pulses are attainable - but below 20 ns, timing becomes inconsistent due to device internal skew and edge-rate limitations.

Does SN74LS122NSR require external pull-up resistors on its Q outputs?

No. The SN74LS122NSR Q outputs are active-low, open-collector compatible only in older variants; the SN74LS122NSR has totem-pole outputs capable of sourcing up to 0.4 mA and sinking up to 8 mA. Pull-ups are unnecessary unless interfacing with higher-voltage logic (e.g., 12 V) - in standard 5 V TTL systems, Q and Q̅ drive directly into LS-TTL or CMOS inputs without external biasing.