Texas Instruments SN74HC74D

Overview

SN74HC74D from Texas Instruments is a dual D-type positive-edge-triggered flip-flop with asynchronous clear and preset inputs per channel, operating across 2 V to 6 V supply voltage and -40°C to +85°C temperature range. It delivers 30 MHz max clock frequency at 4.5 V, 39 ns typical propagation delay (CLK to Q), and supports fanout of up to 10 LSTTL loads. It is used in digital logic circuits for clock division and momentary-to-toggle switch conversion.

For engineers reviewing the SN74HC74D datasheet, SN74HC74D pinout, SN74HC74D application, or SN74HC74D equivalent, this page provides verified functional identity, SOIC-14 package mapping, timing parameters (tsu = 20 ns, th = 0 ns at 4.5 V), output drive capability (±4 mA), and real-world implementation guidance for toggle and divide-by-2 use cases.

Technical Context

The SN74HC74D implements two independent CMOS D-flip-flops with fully asynchronous active-low preset (PRE) and clear (CLR) controls, enabling immediate state override regardless of clock edge. Each channel features buffered standard CMOS inputs and balanced push-pull outputs capable of sourcing/sinking ±4 mA at 4.5 V.

Its operation relies on precise positive-edge clock triggering with setup time (20 ns min at 4.5 V) and zero hold time, allowing reliable data capture without timing margin constraints on data stability after CLK↑. The device uses no internal feedback paths beyond the Q–D connection required for toggle mode.

Key Specifications

Pinout & Package

SN74HC74D is housed in a 14-pin SOIC (Small Outline Integrated Circuit) package measuring 8.70 mm × 3.90 mm, with standard JEDEC MS-012AC footprint and 1.27 mm lead pitch. Thermal resistance RθJA is 133.6 °C/W, requiring minimal heatsinking in typical logic-density layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC74D, SN74HCT74D offers TTL input compatibility at the cost of slightly higher static current, while MC74HC74AD provides identical electrical behavior with alternate supply-chain assurance and optional automotive qualification - both require no schematic or layout changes.

Availability

SN74HC74D is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, and consumer electronics requiring stable component supply, long-term manufacturability, and RoHS-compliant packaging.

Supply support for SN74HC74D 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 specializing in analog, embedded processing, and logic solutions, with over 50 years of leadership in industry-standard logic families.

The SN74HC74D belongs to TI's 74HC high-speed CMOS logic portfolio, designed specifically for low-power, pin-compatible upgrades to legacy TTL-based digital systems in industrial, automotive, and communications equipment.

FAQ

What is the maximum clock frequency supported by the SN74HC74D?

The SN74HC74D supports a maximum clock frequency of 31 MHz at 4.5 V supply and 25°C ambient temperature, dropping to 25 MHz across the full -40°C to +85°C operating range. This rating is guaranteed by timing specifications including minimum pulse width (16 ns for CLK high/low) and setup time (20 ns). Exceeding this frequency may result in metastability or incorrect state capture in the SN74HC74D.

Does the SN74HC74D require external pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs of the SN74HC74D must be terminated to either VCC or GND to prevent floating nodes that cause undefined logic states, increased power consumption, or oscillation. TI recommends 10-kΩ resistors for default HIGH (pull-up) or LOW (pull-down) biasing. Leaving inputs unconnected violates the SN74HC74D's recommended operating conditions and risks erratic behavior in the SN74HC74D.

Can the SN74HC74D operate reliably at 3.3 V supply voltage?

Yes, the SN74HC74D is fully specified for operation from 2 V to 6 V, including 3.3 V. At 3.3 V, VIH is 2.31 V min and VIL is 1.09 V max, ensuring robust noise margins with standard 3.3 V CMOS drivers. Propagation delay increases to ~50 ns and max clock frequency reduces to ~15 MHz, both within datasheet limits for the SN74HC74D.

What is the purpose of the inverted output (Q̅) pins on the SN74HC74D?

The inverted output (Q̅) pins on the SN74HC74D provide complementary logic states without requiring external inverters. This enables direct implementation of toggle mode (D = Q̅), JK-equivalent behavior, differential signaling, or active-low control signals. Using Q̅ avoids added propagation delay, board space, and power consumption associated with discrete inverters in the SN74HC74D application.

How does the SN74HC74D handle power-on reset behavior?

The SN74HC74D has no built-in power-on reset; its initial state is undefined. To ensure predictable startup, an external RC-based power-on reset circuit must assert the CLR (pin 1 or 13) or PRE (pin 4 or 10) inputs low for >100 ns after VCC reaches 2 V. TI provides reference schematics using resistor-capacitor networks tied to CLR for reliable initialization of the SN74HC74D in production systems.