Texas Instruments SN74LS377NSR

Overview

SN74LS377NSR from Texas Instruments is an octal D-type flip-flop with common clock enable, designed for synchronous data latching in TTL-level digital systems. It features 8 independent edge-triggered storage elements, 20-pin SOP package, 0–70°C operating temperature, and guaranteed 25 ns maximum propagation delay (t_PLH/t_PHL) at V_CC = 5 V. It is used in address/data register buffering, bus interface control, and state-holding logic in industrial controllers and legacy computing peripherals.

For engineers reviewing the SN74LS377NSR datasheet, SN74LS377NSR pinout, SN74LS377NSR application, or SN74LS377NSR equivalent, key selection considerations include its single-enable synchronous latch behavior, TTL-compatible input thresholds, 20-pin SOP footprint compatibility with legacy board layouts, and availability in RoHS-compliant tape-and-reel packaging for automated assembly.

Technical Context

The SN74LS377NSR implements eight identical D-type flip-flops sharing a common clock (CLK) and a single active-high output enable (OE) signal. All flip-flops trigger on the rising edge of CLK, and outputs are three-state controlled by OE - when OE is high, Q outputs are high-impedance; when low, they reflect stored D inputs. No internal reset or preset is provided.

It operates strictly within the standard TTL voltage domain: V_CC = 4.75–5.25 V, input HIGH threshold ≥ 2.0 V, input LOW threshold ≤ 0.8 V, and output drive capability of –0.4 mA (I_OH) and 8 mA (I_OL). Its timing is characterized for commercial temperature range only (0 to 70°C), distinguishing it from military-grade SN54LS377 variants rated for –55 to 125°C.

Key Specifications

Pinout & Package

SOP-20 (NS) package: 20-pin small-outline plastic package with gull-wing leads, 12.0 mm center-to-center pitch, 0.300" body width, and moisture sensitivity level 1 (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal D-type latch applications.

Compared with SN74LS377NSR, SN74LS373N offers transparent latching without clock dependency but lacks edge-triggered synchronization, while SN74LS273N adds reset capability at the cost of losing integrated bus isolation - making SN74LS377NSR optimal for clock-synchronized, bus-shared register applications requiring minimal external components.

Availability

SN74LS377NSR is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, legacy computer bus interface, and automated test fixture control requiring stable component supply and long-term production continuity.

Supply support for SN74LS377NSR 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, automotive, and consumer design support.

The SN74LS377NSR belongs to TI's legacy 74LS logic family, developed for robust, low-power TTL-compatible digital interfacing in systems where reliability, timing predictability, and backward compatibility are prioritized over speed or power efficiency.

FAQ

What is the maximum clock frequency supported by the SN74LS377NSR?

The SN74LS377NSR does not specify a maximum clock frequency in its datasheet; instead, it guarantees a maximum propagation delay of 25 ns (t_PLH/t_PHL) under standard conditions. This implies reliable operation up to approximately 20 MHz in well-designed circuits with proper setup/hold timing margins. System-level frequency limits depend on external logic delays and PCB trace lengths, not an intrinsic clock rating of the SN74LS377NSR itself.

Does the SN74LS377NSR have built-in reset or clear functionality?

No, the SN74LS377NSR does not include reset (CLR) or preset inputs. It is a pure edge-triggered D-type flip-flop with only clock (CLK), data (D1–D8), output enable (OE), and power (V_CC/GND) terminals. Any reset functionality must be implemented externally - for example, by forcing D inputs low before the next clock edge or using upstream logic to preload known states. This distinguishes the SN74LS377NSR from variants like SN74LS273N which integrate asynchronous clear.

Can the SN74LS377NSR be used in place of SN74LS377N on the same PCB?

Yes, the SN74LS377NSR is a direct drop-in replacement for SN74LS377N in terms of logic function, pinout, and DC electrical characteristics. Both use identical 20-pin configurations (SOIC-20 for NSR, PDIP-20 for N), share the same V_CC, GND, CLK, D, Q, and OE pin assignments, and operate over the same 0–70°C temperature range. The only physical difference is package type - SOP vs. through-hole - so board redesign is required unless the PCB includes dual-footprint land patterns.

Is the SN74LS377NSR compatible with 3.3 V logic systems?

No, the SN74LS377NSR is not compatible with 3.3 V logic systems. It is a standard LS-TTL device requiring a 4.75–5.25 V supply and exhibiting TTL input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Driving its inputs from 3.3 V CMOS outputs may result in marginal or non-functional HIGH recognition, and its 5 V outputs exceed absolute maximum ratings of most 3.3 V receivers. Level-shifting circuitry is mandatory for interoperability with 3.3 V systems.

What is the recommended decoupling for the SN74LS377NSR?

A minimum of one 0.1 µF ceramic capacitor placed as close as possible to the V_CC (pin 20) and GND (pin 10) pins is recommended for the SN74LS377NSR. For boards with multiple LS-TTL devices, add a bulk 4.7–10 µF tantalum or aluminum electrolytic capacitor near the power entry point. Avoid shared vias between decoupling caps and IC power pins, and route GND connections directly to the nearest ground plane to minimize inductance and suppress switching noise that could affect SN74LS377NSR timing stability.