Texas Instruments SN74LS378DR

Overview

SN74LS378DR from Texas Instruments is a hex D-type flip-flop with common clock enable, designed for synchronous data latching in TTL-level digital logic systems. It features six independent edge-triggered D flip-flops, 16-pin SOIC package, 0–70°C operating temperature, and typical propagation delay of 25 ns at V_CC = 5 V. It is used in address/data register staging, bus interface control, and clock-synchronized state storage.

For engineers reviewing the SN74LS378DR datasheet, SN74LS378DR pinout, SN74LS378DR application, or SN74LS378DR equivalent, key selection considerations include its enable-controlled synchronous operation, TTL-compatible input thresholds, DC supply current under load, maximum clock frequency capability, and compatibility with legacy 74LS logic families in industrial control and instrumentation designs.

Technical Context

The SN74LS378DR implements six identical D-type flip-flops sharing a single active-high clock enable (CE) input and a common clock (CLK) input. Each flip-flop captures the logic level present at its D input on the rising edge of CLK only when CE is high; otherwise, outputs hold their previous state.

This architecture supports deterministic, cycle-aligned data capture across multiple channels without requiring individual clock gating. Its TTL input structure ensures compatibility with standard LS-series drivers, while output drive capability meets ±8 mA sink/source specifications for direct fanout to other 74LS inputs.

Key Specifications

Pinout & Package

SN74LS378DR is housed in a 16-pin small-outline integrated circuit (SOIC) package with 1.27 mm pitch, 2.65 mm max height, and JEDEC MS-013 compliant outline. Pin 1 is located in quadrant Q1 per TI tape-and-reel specification.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar hex D-type flip-flop applications.

Compared with SN74LS175N and SN74LS273N, the SN74LS378DR uniquely balances 6-bit width, integrated clock enable, and SOIC packaging - making it optimal for space-constrained, enable-gated register applications where neither quad nor octal configurations fully match system requirements.

Availability

SN74LS378DR is available at Aetrix Electronics and suitable for industrial PLC I/O modules, digital test equipment, legacy bus interface designs, and microcontroller peripheral expansion requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS378DR 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 solutions for industrial, automotive, and communications markets.

The SN74LS378DR belongs to TI's legacy 74LS logic family, engineered for robust TTL-level digital interfacing in cost-sensitive, reliability-critical control and instrumentation systems deployed from the 1980s onward.

FAQ

What is the maximum clock frequency supported by SN74LS378DR?

The SN74LS378DR has a maximum recommended clock frequency of 20 MHz, derived from its 25 ns maximum propagation delay (t_PLH/t_PHL) and setup/hold timing constraints. Operation above this frequency risks timing violations and metastability. This limit assumes proper PCB layout, decoupling, and TTL-compatible drive strength on CLK and CE lines. The SN74LS378DR does not specify a guaranteed minimum pulse width for CE deassertion, so designers must ensure CE remains stable for at least one full clock cycle before re-enabling.

Does SN74LS378DR provide complementary (Q̅) outputs?

No, the SN74LS378DR provides only true (Q) outputs for each of its six D flip-flops - there are no dedicated inverted (Q̅) outputs on this device. If complementary outputs are required, external inverters or a different part such as the SN74LS112 (dual J-K flip-flop with Q/Q̅) must be used. The SN74LS378DR's pinout and functional description confirm output terminals 9–14 are labeled Q1–Q6 only, with no corresponding Q̅ pins allocated.

Can SN74LS378DR operate with a 3.3 V supply?

No, the SN74LS378DR is specified exclusively for 4.75 V to 5.25 V operation and is not compatible with 3.3 V logic systems. Its TTL input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V) and internal bipolar transistor design require nominal 5 V biasing. Attempting to power the SN74LS378DR from 3.3 V will result in unreliable switching, excessive propagation delay, or complete failure to toggle. For 3.3 V systems, consider LVCMOS alternatives like SN74LVC174A.

Is SN74LS378DR pin-compatible with SN74LS377 or SN74LS379?

No, the SN74LS378DR is not pin-compatible with SN74LS377 (octal) or SN74LS379 (quad); they differ in flip-flop count, pin assignments, and package pinouts. SN74LS377 uses a 20-pin package (SOIC-20 or PDIP-20), while SN74LS378DR is 16-pin SOIC. SN74LS379 is also 16-pin but implements quad D flip-flops with different terminal mapping. Substituting any of these parts without board redesign will cause incorrect connections and functional failure. The SN74LS378DR's unique 6-bit configuration and 16-pin layout are not shared across the family.

What is the purpose of the CE (Clock Enable) pin on SN74LS378DR?

On the SN74LS378DR, the CE (Clock Enable) pin is an active-high control that gates the clock signal to all six D flip-flops: when CE = HIGH, rising CLK edges trigger data capture at the D inputs; when CE = LOW, all outputs retain their current state regardless of CLK activity. This allows synchronous data latching to be enabled or disabled without stopping the clock source - essential for time-multiplexed register access, gated test modes, or power-aware operation. CE is internally wired to inhibit the clock path, not as a simple AND gate, ensuring clean hold behavior per TI's SDLS167 datasheet.