Texas Instruments SN74HCT74D

Overview

SN74HCT74D from Texas Instruments is a dual D-type positive-edge-triggered flip-flop with independent preset (PRE) and clear (CLR) inputs, operating at 4.5–5.5 V supply, delivering 17 ns typical propagation delay (tpd), ±4-mA output drive at 5 V, and TTL-compatible input thresholds. It serves as a synchronous storage element in digital control logic, clock-domain synchronization, and state-machine sequencing.

For engineers reviewing the SN74HCT74D datasheet, SN74HCT74D pinout, SN74HCT74D application, or SN74HCT74D equivalent, this page provides verified functional identity, SOIC-14 package mapping, timing behavior under 5-V operation, and validated alternative options for logic-level storage and edge-triggered state retention.

Technical Context

The SN74HCT74D implements two fully independent D-type flip-flops sharing no internal coupling-each with dedicated PRE, CLR, CLK, D, Q, and Q̅ terminals. Clock triggering occurs at a fixed voltage threshold (~1.3 V / ~3 V), decoupled from input rise time, enabling robust edge detection across varying signal slew rates.

Its asynchronous PRE/CLR inputs override clocked data transfer, forcing Q to high or low regardless of CLK or D states. When both PRE and CLR are high, data at D is latched on the rising edge of CLK, provided setup (12–15 ns) and hold (0 ns) timing requirements are met.

Key Specifications

Pinout & Package

SN74HCT74D is housed in a 14-pin SOIC (Small Outline Integrated Circuit) package measuring 8.65 mm × 3.90 mm, with 1.27-mm lead pitch and 1.75-mm maximum height. The package is RoHS-compliant, moisture-sensitive level 1, and rated for −40°C to +85°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT74DR, SN74HCT74D offers identical functionality but differs in packaging format and availability channel; compared with SN74HC74D, it delivers faster timing, tighter noise margins, and guaranteed TTL compatibility-making it the optimal choice for legacy 5-V control systems demanding reliability and interoperability.

Availability

SN74HCT74D is available at Aetrix Electronics and suitable for industrial control logic, digital signal synchronization, state machine sequencing, and LED/display driver applications requiring stable component supply and long-term sourcing continuity.

Supply support for SN74HCT74D 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 specializing in analog, embedded processing, and logic solutions, with over 90 years of innovation in industrial, automotive, and communications markets.

The SN74HCT74D belongs to TI's 74HCT logic family-designed specifically for TTL-compatible 5-V digital systems requiring low power, high noise immunity, and robust edge-triggered storage in harsh electromagnetic environments.

FAQ

What is the maximum clock frequency supported by the SN74HCT74D?

The SN74HCT74D supports a maximum clock frequency of 22 MHz at VCC = 5.5 V and TA = 25°C, based on its 17 ns typical propagation delay and verified switching characteristics. At 4.5 V, fmax drops to 18 MHz. This makes SN74HCT74D suitable for medium-speed synchronous logic in industrial controllers and interface bridges where deterministic timing is essential.

Does the SN74HCT74D require external pull-up or pull-down resistors on unused inputs?

Yes-per TI's design guidance, all unused inputs of the SN74HCT74D must be tied to either VCC or GND to prevent floating nodes that cause undefined outputs, increased ICC, or oscillation. For example, an unconnected 2PRE should be pulled high to disable preset functionality and avoid unintended state changes during operation of SN74HCT74D.

Can the SN74HCT74D operate reliably at 3.3 V?

No-the SN74HCT74D is specified only for 4.5 V to 5.5 V operation. Its TTL-compatible input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) and internal HCT architecture require minimum 4.5 V to guarantee proper logic levels, noise margins, and output drive. For 3.3-V systems, consider SN74LVC74A or SN74AUP1G74 instead of SN74HCT74D.

How does the asynchronous clear (CLR) function interact with the clock signal in the SN74HCT74D?

In the SN74HCT74D, the asynchronous CLR input overrides all clock activity: when CLR is low, Q is forced LOW and Q̅ HIGH immediately-regardless of CLK state, D value, or edge timing. This action occurs independently per channel and takes precedence over both clocked data transfer and preset assertion, making it ideal for emergency reset functions in safety-critical logic.

Is the SN74HCT74D pin-compatible with the SN74LS74A?

Yes-the SN74HCT74D uses the same 14-pin SOIC footprint and pinout as SN74LS74A, including identical assignments for PRE, CLR, CLK, D, Q, and Q̅ per channel. However, SN74HCT74D draws significantly less quiescent current (40 μA vs. 15 mA), offers higher noise immunity, and eliminates LS-family ground bounce concerns-making it a direct drop-in upgrade in most 5-V TTL systems.