Texas Instruments SN74LS374NS

Overview

SN74LS374NS from Texas Instruments is an octal positive-edge-triggered D-type flip-flop with 3-state bus-driver outputs, designed for synchronous data latching in TTL-level digital systems. It features 8 independent D-type registers, clock-enable input with hysteresis for noise immunity, and buffered output-control (OC) for high-impedance bus isolation. Used in legacy microprocessor address/data bus buffering and I/O port expansion.

For engineers reviewing the SN74LS374NS datasheet, SN74LS374NS pinout, SN74LS374NS application, or SN74LS374NS equivalent, key selection criteria include its 20-pin PDIP-compatible SOP (NS) package, 5 V ±5% supply operation, 20 ns data setup time, and 3-state output timing compatibility with LS-TTL bus architectures.

Technical Context

The SN74LS374NS implements eight edge-triggered D flip-flops sharing a common clock (CLK) and output-control (OC) signal. Each flip-flop captures the logic state present at its D input on the rising edge of CLK, with OC enabling/disabling all Q outputs simultaneously without affecting internal register state.

Its inputs feature Schmitt-trigger hysteresis on CLK and OC to improve ac/dc noise rejection by ~400 mV, while P-N-P input structure reduces DC loading on data lines. The 3-state outputs drive highly capacitive or low-impedance buses directly, eliminating need for external pull-ups or interface buffers.

Key Specifications

Pinout & Package

SN74LS374NS uses a 20-pin Small Outline Package (SOP-NS), pin-compatible with PDIP-20 and SOIC-20 footprints. Thermal resistance θJA = 60°C/W enables operation up to 70°C ambient without forced cooling.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS374NS, SN74LS374N trades thermal efficiency for mechanical serviceability, while SN74LS374DWR delivers superior thermal performance and manufacturability-making the NS variant optimal for space-constrained, hand-assembled, or legacy-replacement use cases.

Availability

SN74LS374NS is available at Aetrix Electronics and suitable for microprocessor bus interfacing, industrial I/O expansion, and legacy memory address latching requiring stable component supply across long-life product cycles.

Supply support for SN74LS374NS 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 solutions for industrial, automotive, and communications markets.

The SN74LS374NS belongs to TI's legacy LS-TTL logic family, engineered specifically for robust, low-power 5 V digital interfacing in mission-critical industrial control and retro-computing applications.

FAQ

What is the primary function of the SN74LS374NS in a digital system?

The SN74LS374NS functions as an octal positive-edge-triggered D-type flip-flop with 3-state outputs. It captures and holds 8 bits of parallel data on the rising edge of its CLK input, then drives them onto a shared bus only when its OC (output control) pin is asserted low. This makes SN74LS374NS ideal for synchronizing data transfers in microprocessor systems, especially where bus isolation and timing determinism are required.

Does the SN74LS374NS support 3.3 V operation?

No, the SN74LS374NS is strictly a 5 V LS-TTL device with recommended operating supply of 4.75 V to 5.25 V. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output drive levels are optimized for 5 V logic families. Applying 3.3 V to VCC will result in undefined behavior, insufficient noise margin, or failure to meet timing specifications. For 3.3 V systems, consider modern alternatives like SN74LVC574A.

How does the hysteresis on the CLK and OC inputs benefit the SN74LS374NS?

The hysteresis on CLK and OC inputs provides ~400 mV of noise immunity, significantly improving rejection of both ac and dc noise on control lines. In real-world applications such as industrial backplanes or motor-drive environments, this prevents false triggering due to ringing or EMI-induced glitches. As a result, SN74LS374NS maintains reliable edge detection and output enable/disable transitions even under electrically harsh conditions.

Can the SN74LS374NS outputs be safely tied together with other 3-state devices on the same bus?

Yes-this is a core design purpose of the SN74LS374NS. Its 3-state outputs allow multiple devices (e.g., multiple SN74LS374NS units or mixed-function buffers) to share a common bus, provided only one device has OC low at any time. When OC is high, outputs enter high-impedance mode and neither load nor drive the bus, eliminating contention. Proper bus arbitration logic must ensure exclusive OC activation.

What is the maximum clock frequency supported by the SN74LS374NS?

The SN74LS374NS supports a maximum clock frequency of 35 MHz under typical conditions (VCC = 5 V, TA = 25°C, RL = 667 Ω, CL = 45 pF). At elevated temperatures or with heavier capacitive loads, the usable frequency decreases due to increased propagation delay. For reliable operation at 35 MHz, ensure clean power delivery, proper PCB layout (short traces, ground plane), and minimal output capacitance.