Texas Instruments SN74AC74NS

Overview

SN74AC74NS from Texas Instruments is a dual positive-edge-triggered D-type flip-flop IC with independent asynchronous clear (CLR) and preset (PRE) inputs per channel, 2V–6V supply operation, 10ns maximum propagation delay at 5V, and complementary Q/Q outputs per stage - used in clock division, toggle-switch conversion, and synchronous state-holding circuits.

For engineers reviewing the SN74AC74NS datasheet, SN74AC74NS pinout, SN74AC74NS application, or SN74AC74NS equivalent, key selection criteria include VCC range compatibility (2–6V), edge-triggered timing behavior, dual-channel independence, asynchronous control logic levels, and SOP-14 package thermal and layout constraints.

Technical Context

The SN74AC74NS implements two fully independent CMOS D-type flip-flops, each with separate active-low asynchronous PRE and CLR inputs, positive-edge-sensitive CLK, and true/complement outputs (Q and Q). No internal inter-channel coupling exists beyond shared VCC and GND rails.

Each flip-flop operates under standard CMOS latching logic: output state updates only on CLK rising edge when both PRE and CLR are high; otherwise, PRE or CLR forces Q/Q to defined states regardless of CLK or D. Input thresholds scale with VCC, supporting mixed-voltage interfacing up to 6V input tolerance.

Key Specifications

Pinout & Package

SN74AC74NS is housed in a 14-pin SOP (Small Outline Package) with 10.2mm × 7.8mm body size and 10.3mm × 5.3mm footprint. The package uses gull-wing leads, is RoHS-compliant, and rated for surface-mount reflow assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC74N and 74LVC74ABQ, the SN74AC74NS uniquely balances wide VCC range (2–6V), high-speed performance (125MHz fmax), and SOP-14 manufacturability - making it optimal for industrial control boards needing mixed-voltage interoperability and legacy PCB compatibility.

Availability

SN74AC74NS is available at Aetrix Electronics and suitable for industrial automation interfaces, legacy system upgrades, and mixed-voltage digital logic design requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74AC74NS 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 decades of experience delivering high-reliability, industry-standard logic families.

The SN74AC74NS belongs to TI's AC-series advanced CMOS logic product line, engineered for high-speed, low-noise, mixed-voltage digital interfacing in industrial, automotive, and communications equipment.

FAQ

What is the maximum clock frequency supported by SN74AC74NS at 5V operation?

The SN74AC74NS supports a maximum clock frequency of 125MHz at VCC = 5V ± 0.5V, as specified in the Switching Characteristics table (Section 5.8). This rating applies under recommended operating conditions with CL = 50pF load and TA = 25°C. Real-world achievable frequency may vary slightly based on PCB layout, decoupling, and temperature, but the 125MHz figure provides a validated design margin for industrial applications using the SN74AC74NS.

Can SN74AC74NS operate with a 3.3V supply while interfacing with 5V logic inputs?

Yes, SN74AC74NS can operate at 3.3V VCC and safely accept 5V logic inputs because its inputs are rated to 6V - exceeding standard 5V TTL and CMOS voltage levels. This allows direct connection to 5V microcontrollers or peripherals without level-shifting circuitry. However, outputs will swing between 0V and ~3.3V, so downstream 5V devices must recognize 3.3V as a valid HIGH level (e.g., 74AC or 74LVC families), which the SN74AC74NS guarantees per its VIH specification.

Does SN74AC74NS require external pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs of SN74AC74NS - including PRE, CLR, D, and CLK pins - must be terminated to either VCC or GND to prevent floating nodes, which could cause excessive current draw, oscillation, or undefined output states. TI recommends 10kΩ pull-up or pull-down resistors for inputs that may be left unconnected during certain modes. Leaving any input floating violates the Recommended Operating Conditions and risks unreliable operation of the SN74AC74NS.

How does the thermal performance of SN74AC74NS compare across different packages?

The SN74AC74NS in NS (SOP-14) package has a junction-to-ambient thermal resistance (RθJA) of 76°C/W, which is lower than SOIC (D, 119.9°C/W) and TSSOP (PW, 145.7°C/W) variants - indicating superior heat dissipation for the same power dissipation. This makes the NS package more suitable for higher ambient temperatures or sustained high-frequency operation. The WQFN (BQA) variant offers the best RθJA (91.3°C/W), but SN74AC74NS specifically refers to the SOP version, not WQFN.

Is SN74AC74NS pin-compatible with other 74AC74 variants like SN74AC74N or SN74AC74D?

Yes, SN74AC74NS is pin-compatible with all 14-pin 74AC74 variants including SN74AC74N (PDIP), SN74AC74D (SOIC), and SN74AC74PW (TSSOP), sharing identical pin numbering, function mapping, and electrical behavior. The "NS" suffix denotes the SOP package, and all share the same logic diagram, timing parameters, and functional truth table. This allows drop-in replacement across packages when board layout permits, preserving design integrity for the SN74AC74NS and its counterparts.