Texas Instruments SN74HC74PW

Overview

SN74HC74PW from Texas Instruments is a dual D-type positive-edge-triggered flip-flop with independent asynchronous preset and clear inputs per channel, operating from 2 V to 6 V supply voltage, supporting clock frequencies up to 36 MHz at 6 V, and rated for -40°C to +85°C industrial temperature range - used in digital logic control, clock division, and switch debouncing circuits.

For engineers reviewing the SN74HC74PW datasheet, SN74HC74PW pinout, SN74HC74PW application, or SN74HC74PW equivalent, key selection considerations include its TSSOP-14 package footprint, dual-channel edge-triggered behavior, asynchronous set/reset timing margins, and compatibility with 5-V and 3.3-V CMOS systems.

Technical Context

The SN74HC74PW implements two fully independent D-type flip-flops, each with separate positive-edge-triggered clock (CLK), data (D), active-low preset (PRE), active-low clear (CLR), true output (Q), and complement output (Q̅). Its CMOS architecture ensures balanced push-pull outputs capable of sourcing/sinking ±4 mA at 4.5 V and ±5.2 mA at 6 V.

Timing is governed by strict setup (tsu = 17 ns min at 6 V), hold (th = 0 ns), and pulse width (tw = 14 ns min for CLK/CLR/PRE) requirements. Propagation delay from CLK to Q is 15 ns typical at 6 V, and maximum clock frequency reaches 36 MHz under recommended conditions.

Key Specifications

Pinout & Package

TSSOP-14 package (5.00 mm × 4.40 mm body size), 0.65 mm lead pitch, surface-mount, moisture-sensitivity level 1 (MSL-1).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC74PW, SN74HCT74PW offers improved input compatibility with older TTL families but consumes more quiescent power, while MC74HC74ADTR2G delivers automotive-grade thermal robustness and qualification at the cost of higher unit price and longer lead times.

Availability

SN74HC74PW is available at Aetrix Electronics and suitable for industrial control panels, consumer appliance logic boards, and test equipment requiring stable component supply across long production lifecycles.

Supply support for SN74HC74PW 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 company headquartered in Dallas, Texas, designing and manufacturing analog, embedded processing, and logic ICs for industrial, automotive, and communications markets.

The SN74HC74PW belongs to TI's 74HC logic family - engineered for high-speed, low-power CMOS operation with TTL-compatible drive strength and wide supply voltage tolerance to simplify mixed-voltage system design.

FAQ

What is the maximum clock frequency supported by the SN74HC74PW?

The SN74HC74PW supports a maximum clock frequency of 36 MHz when operated at VCC = 6 V and TA = –40°C to +85°C. At 4.5 V, the guaranteed maximum is 25 MHz, and at 2 V it drops to 5 MHz. These values are specified in the Switching Characteristics table (Section 6.9) of the official datasheet and reflect worst-case timing under recommended operating conditions - not typical or ideal-lab performance.

Does the SN74HC74PW require external pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs of the SN74HC74PW must be terminated to either VCC or GND to prevent floating states that cause excessive current draw, oscillation, or undefined outputs. TI recommends 10-kΩ resistors for unused PRE, CLR, D, or CLK pins - connecting PRE/CLR to VCC (inactive high) and D/CLK to GND or VCC depending on desired default logic level. Leaving inputs unconnected violates the Absolute Maximum Ratings and risks device malfunction.

Can the SN74HC74PW drive LED indicators directly?

No, the SN74HC74PW is not designed to drive LEDs directly. Its output current capability is limited to ±4 mA at 4.5 V and ±5.2 mA at 6 V - insufficient for typical indicator LEDs requiring 10–20 mA. Attempting direct LED drive risks exceeding absolute maximum output current (±25 mA) and may cause output voltage droop, timing violations, or accelerated wear. Use a discrete transistor or dedicated LED driver IC instead.

What is the purpose of the Q̅ (complement) output on the SN74HC74PW?

The Q̅ output on the SN74HC74PW provides the logical inverse of the Q output and serves multiple design functions: enabling toggle-mode operation (by feeding Q̅ back to D), supporting differential signaling paths, simplifying combinational logic (e.g., NAND/NOR gates), and facilitating synchronous reset/set verification. It is not merely redundant - it eliminates external inverters in common configurations like divide-by-2 counters or JK-equivalent behavior, reducing component count and propagation delay.

Is the SN74HC74PW pin-compatible with the SN74LS74A?

No, the SN74HC74PW is not pin-compatible with the SN74LS74A. While both are dual D-type flip-flops in 14-pin packages, the SN74LS74A uses a PDIP or SOIC package with different pin assignments - notably, its VCC and GND pins are located at positions 14 and 7, whereas the SN74HC74PW in TSSOP-14 places VCC at pin 14 and GND at pin 7 but has distinct internal routing and electrical characteristics. Substituting them requires PCB redesign and validation of timing, voltage thresholds, and drive strength.