Texas Instruments SN74LS122NG4

Overview

SN74LS122NG4 from Texas Instruments is a retriggerable monostable multivibrator IC in a 14-pin PDIP 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, used for pulse shaping and timing control in legacy TTL-based industrial control logic.

For engineers reviewing the SN74LS122NG4 datasheet, SN74LS122NG4 pinout, SN74LS122NG4 application, or SN74LS122NG4 equivalent, this page delivers verified functional identity, confirmed package mapping (PDIP-14), validated timing parameters, and real-world design context for legacy system maintenance and drop-in replacement evaluation.

Technical Context

The SN74LS122NG4 implements dual independent retriggerable monostable multivibrators with active-low clear and trigger inputs, enabling precise one-shot pulse generation that resets on each new trigger edge before timeout completion. Its TTL-compatible input thresholds and complementary push-pull outputs support direct interfacing with 74LS/74S logic families.

Timing duration is externally set via R_EXT and C_EXT, with nominal output pulse width t_W ≈ 0.3 × R_EXT(kΩ) × C_EXT(µF); the device exhibits no internal timing resistor and requires no external diode for retriggering-unlike non-retriggerable variants such as SN74LS123.

Key Specifications

Pinout & Package

SN74LS122NG4 is housed in a 14-pin plastic dual in-line package (PDIP-N), 0.3-inch body width, with standard DIP pin spacing (0.1 inch), lead finish NiPdAu, RoHS compliant, and rated for 0°C to 70°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS122NG4, SN74LS123N offers simpler timing behavior but cannot extend pulses on successive triggers, while SN74LS221N provides enhanced noise rejection and flexible timing at the cost of PCB layout changes and increased component count.

Availability

SN74LS122NG4 is available at Aetrix Electronics and suitable for industrial control panel timing, legacy test equipment pulse generation, electromechanical system debounce, and legacy communication interface handshaking requiring stable component supply across long-lifecycle programs.

Supply support for SN74LS122NG4 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 SN74LS122NG4 belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power TTL-compatible timing and sequencing in cost-sensitive, non-volatile industrial control systems.

FAQ

What is the primary function of the SN74LS122NG4?

The SN74LS122NG4 is a dual retriggerable monostable multivibrator IC that generates precise, user-defined output pulses in response to input triggers. Each channel operates independently, allowing simultaneous timing control for two distinct signals. Its retriggerable architecture ensures the output pulse width restarts on every new trigger edge, making it ideal for pulse conditioning and synchronization tasks in legacy TTL systems. The SN74LS122NG4 does not require external diodes for retriggering, simplifying circuit design compared to non-retriggerable alternatives.

Does the SN74LS122NG4 support 3.3-V operation?

No, the SN74LS122NG4 is strictly a 5-V TTL device with a specified supply range of 4.75 V to 5.25 V. It is not characterized for 3.3-V operation, and attempting to power it at lower voltages will result in undefined timing behavior, degraded noise margins, and potential failure to meet output drive specifications. For 3.3-V systems, modern alternatives such as the SN74LVC1G123 or SN74LV123A should be evaluated instead of the SN74LS122NG4.

How is timing duration set on the SN74LS122NG4?

Timing duration on the SN74LS122NG4 is set externally using a resistor (R_EXT) and capacitor (C_EXT) connected to dedicated pins per channel. The nominal output pulse width is calculated as t_W ≈ 0.3 × R_EXT(kΩ) × C_EXT(µF). Unlike some monostables, the SN74LS122NG4 does not include an internal timing resistor, so both components must be provided. Values are selected based on required pulse width, stability needs, and capacitor leakage characteristics-ceramic or film types are recommended for best repeatability.

Can the SN74LS122NG4 replace the SN74LS123N in an existing design?

No, the SN74LS122NG4 cannot directly replace the SN74LS123N because they implement fundamentally different timing behaviors: the SN74LS122NG4 is retriggerable, while the SN74LS123N is non-retriggerable. Swapping them would alter system timing response-e.g., consecutive triggers would extend the pulse in SN74LS122NG4 but be ignored after the first in SN74LS123N. Pin compatibility exists (both are 14-pin PDIP), but functional mismatch makes substitution unsafe without circuit and firmware validation. Always verify timing diagrams before substituting the SN74LS122NG4 for SN74LS123N.

What is the maximum output current capability of the SN74LS122NG4?

The SN74LS122NG4 provides ±8 mA output drive capability-specifically, I_OL = 8 mA (sink) and I_OH = –0.4 mA (source) under standard test conditions (V_CC = 5 V, T_A = 25°C). This allows direct driving of up to 10 standard 74LS inputs or small indicator LEDs with appropriate current-limiting resistors. Exceeding these limits risks output voltage degradation or thermal stress. For higher-current loads, buffer stages such as ULN2003 or discrete transistors are recommended alongside the SN74LS122NG4.