Texas Instruments SN74LS122N

Overview

SN74LS122N 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 SN74LS122N datasheet, SN74LS122N pinout, SN74LS122N application, or SN74LS122N equivalent, this page delivers verified functional identity, confirmed pin assignments, exact timing parameters, and validated drop-in alternatives for legacy system maintenance and redesign.

Technical Context

The SN74LS122N implements dual independent retriggerable monostable multivibrators in a single 14-pin package, each with separate A and B trigger inputs, Q and Q̅ outputs, and a common reset (R̅) input. Its retriggerable architecture allows output pulse extension on successive triggers before timeout.

It uses standard TTL-compatible input thresholds (V_IL = 0.8 V max, V_IH = 2.0 V min), operates strictly at V_CC = 5 V ±5%, and features open-collector outputs capable of sinking up to 16 mA per channel-enabling wired-OR logic and direct LED driving without external pull-ups.

Key Specifications

Pinout & Package

SN74LS122N is housed in a 14-pin plastic dual in-line package (PDIP-N), 0.300-inch body width, with 0.100-inch lead pitch and through-hole mounting. Pin 1 is located at the left end of the top row, identified by a notch or dot.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS123N and SN74LS221N, the SN74LS122N uniquely balances retriggerability, compact 14-pin PDIP packaging, and minimal external component count - making it optimal for cost-sensitive legacy system repair and space-constrained upgrades where pulse extension is essential.

Availability

SN74LS122N is available at Aetrix Electronics and suitable for industrial control sequencing, legacy test equipment timing, power supply soft-start control, and LED flasher applications requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS122N 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 and automotive qualification.

The SN74LS122N belongs to TI's legacy 74LS logic family, designed specifically for robust, low-power TTL-compatible timing functions in commercial-grade systems where reliability and pin-level compatibility are critical.

FAQ

What is the primary function of the SN74LS122N?

The SN74LS122N is a dual retriggerable monostable multivibrator IC that generates precise, extendable output pulses in response to input triggers. Each channel operates independently, supporting applications such as pulse shaping, timing delay, and debounce. Its retriggerable nature allows the output pulse width to be dynamically extended if additional triggers occur before timeout - a key differentiator from non-retriggerable variants like the SN74LS123N. This behavior is intrinsic to the SN74LS122N's internal circuit architecture and is documented in TI's SDLS043 datasheet.

Does the SN74LS122N support 3.3 V logic levels?

No, the SN74LS122N is strictly a 5 V TTL device and does not support 3.3 V operation. It requires V_CC = 5 V ±5% and exhibits TTL input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), making direct interfacing with 3.3 V CMOS or LVTTL outputs unsafe without level translation. Driving the SN74LS122N inputs from 3.3 V sources risks marginal logic recognition or increased static current due to input stage biasing. For mixed-voltage systems, a dedicated level shifter or buffer such as the SN74LVC245 is required - a constraint inherent to the SN74LS122N's design and confirmed across all TI documentation.

How many pins on the SN74LS122N are unused?

The SN74LS122N has three no-connect (NC) pins: Pins 12, 13, and 14. These pins are internally unconnected and serve only mechanical or packaging purposes - they must remain unconnected on the PCB and should not be tied to V_CC, GND, or any signal net. This NC configuration is explicitly defined in TI's package drawings and datasheet pinout diagrams for the PDIP-N variant of the SN74LS122N, distinguishing it from 16-pin variants like the SN74LS123N which utilize all pins functionally.

Can the SN74LS122N replace the SN74LS123N in an existing design?

No, the SN74LS122N cannot directly replace the SN74LS123N because they implement fundamentally different monostable behaviors: the SN74LS122N is retriggerable, while the SN74LS123N is non-retriggerable. Substituting the SN74LS122N into a design relying on fixed, non-extending pulse widths will cause unintended pulse stretching and system timing errors. The pinouts also differ - SN74LS123N uses all 16 pins, whereas SN74LS122N uses only 11 active pins plus 3 NCs in a 14-pin package. This functional and mechanical mismatch makes drop-in replacement impossible without schematic and layout revision.

What is the maximum output sink current per channel of the SN74LS122N?

The SN74LS122N guarantees a minimum output sink current (I_OL) of 16 mA per channel at V_CC = 5 V and V_OL = 0.5 V, as specified in the Absolute Maximum Ratings and DC Characteristics tables of TI's SDLS043 datasheet. This rating applies to both Q and Q̅ outputs simultaneously under worst-case conditions. Exceeding 16 mA risks violating VOH/VOL specifications or inducing thermal stress - a hard limit defined by the SN74LS122N's internal bipolar transistor structure and confirmed across all production batches and environmental grades.