Texas Instruments SN74HCT74DT

Overview

SN74HCT74DT 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 V to 5.5 V supply voltage, delivering ±4-mA output drive at 5 V, with typical propagation delay of 17 ns and low input current ≤1 μA. It serves as a synchronous storage element in digital control logic, clock-domain synchronization, and state-machine sequencing in industrial PLC modules.

For engineers reviewing the SN74HCT74DT datasheet, SN74HCT74DT pinout, SN74HCT74DT application, or SN74HCT74DT equivalent, this page provides verified functional behavior, TTL-compatible input thresholds, timing margins under 5-V operation, and validated package-specific thermal metrics for SOIC-14 layout integration.

Technical Context

The SN74HCT74DT implements two fully independent edge-triggered storage cells, each with asynchronous active-low PRE and CLR inputs that override clocked data transfer. Its triggering occurs at a fixed voltage threshold (~1.3 V / ~3.0 V), decoupled from CLK rise time, enabling robust operation across varying signal slew rates.

Each flip-flop supports TTL-voltage-compatible inputs (VIH = 2.0 V min, VIL = 0.8 V max) and drives up to 10 LSTTL loads. The device exhibits low static power consumption (ICC ≤ 40 μA max) and operates over –40°C to +85°C, meeting industrial-grade reliability requirements without derating.

Key Specifications

Pinout & Package

SN74HCT74DT is supplied in a 14-pin SOIC (D) package with nominal body size 8.65 mm × 3.90 mm and maximum height 1.75 mm, suitable for surface-mount reflow assembly per JEDEC MS-012AB.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT74DT, SN74HCT74DR offers identical performance in a production-optimized reel format, while 74HCT74PW trades package size for marginally lower thermal efficiency-neither is pin-compatible with SN74HCT74DT due to differing SOIC vs. TSSOP land patterns.

Availability

SN74HCT74DT is available at Aetrix Electronics and suitable for industrial control sequencing, digital signal synchronization, test equipment logic control, and legacy system interface adapter applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74HCT74DT 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 50 years of innovation in industrial and automotive electronics.

The SN74HCT74DT belongs to TI's HCT logic family, designed specifically for TTL-compatible 5-V systems requiring low power, high noise immunity, and seamless interoperability with legacy digital infrastructure.

FAQ

What is the maximum clock frequency supported by SN74HCT74DT?

The SN74HCT74DT supports a maximum clock frequency of 22 MHz at VCC = 5.5 V and TA = 25°C, as specified in the switching characteristics table. This limit derives from the 17-ns typical propagation delay and required setup/hold timing margins. At 4.5 V, fmax reduces to 18 MHz due to slower internal switching. System-level timing must account for worst-case tpd (40 ns) and external trace delays.

Does SN74HCT74DT require external pull-up resistors on PRE and CLR inputs?

No, SN74HCT74DT does not require external pull-up resistors on PRE and CLR inputs when actively driven, as these are standard CMOS inputs with leakage ≤1 μA. However, unused PRE/CLR pins must be tied to VCC (not left floating) to prevent undefined states. TI recommends direct connection to VCC or GND per application report SCBA004.

Can SN74HCT74DT operate reliably at 3.3 V supply voltage?

No, SN74HCT74DT is not rated for 3.3 V operation. Its recommended operating range is strictly 4.5 V to 5.5 V, and absolute maximum ratings prohibit sustained operation below 4.5 V. Attempting 3.3 V supply may result in marginal logic thresholds, increased propagation delay, or failure to meet setup/hold times. Use SN74LVC74A for 3.3-V compatible dual D-flip-flops.

What is the purpose of the NC (no-connect) pin on SN74HCT74DT?

SN74HCT74DT has no NC pin - all 14 pins in its SOIC package are electrically assigned per the functional pinout: two D inputs, two Q outputs, two Q̅ outputs, two CLK inputs, two PRE inputs, two CLR inputs, one VCC, and one GND. The "NC" designation appears only in alternate packages (e.g., LCCC FK) and does not apply to SN74HCT74DT.

How does SN74HCT74DT handle simultaneous assertion of PRE and CLR?

When both PRE and CLR are low on the same flip-flop, the SN74HCT74DT enters a nonstable state where both Q and Q̅ go high (per the function table). This condition is transient and resolves to a defined state (Q = 1, Q̅ = 1) only while PRE and CLR remain asserted; upon release, the output reverts unpredictably based on internal race conditions. TI explicitly warns against relying on this state in functional designs.