Texas Instruments SN74HCS74DR

Overview

SN74HCS74DR from Texas Instruments is a dual D-type positive-edge-triggered flip-flop with Schmitt-trigger inputs, asynchronous clear and preset, operating from 2 V to 6 V. It delivers ±7.8-mA output drive at 6 V, supports –40°C to +125°C ambient operation, and enables reliable clock division or momentary-to-toggle switch conversion in noisy industrial control interfaces.

For engineers reviewing the SN74HCS74DR datasheet, SN74HCS74DR pinout, SN74HCS74DR application, or SN74HCS74DR equivalent, key selection criteria include its hysteresis (ΔVT ≥ 0.6 V at 6 V), low ICC (≤ 2 µA), 105-MHz max switching frequency, and SOIC-14 package compatibility with legacy board layouts.

Technical Context

The SN74HCS74DR implements two independent CMOS D-type flip-flops with fully asynchronous PRE/CLR control and Schmitt-trigger input thresholds (VT+ = 2.1–4.2 V, VT− = 1.2–3.0 V at 6 V). Each channel responds only to the rising edge of CLK, with setup time as low as 6 ns and hold time of 0 ns at 6 V.

Its balanced push-pull outputs provide symmetrical sourcing/sinking capability, while input hysteresis ensures robust operation with slow-rising signals (e.g., mechanical switch debouncing) and noise immunity up to ±0.8 V peak-to-peak at 6 V supply.

Key Specifications

Pinout & Package

SN74HCS74DR uses a 14-pin SOIC (D) package measuring 8.70 mm × 3.90 mm with standard JEDEC MS-012 footprint and 1.27-mm pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC74DR, SN74HCS74DR adds essential noise immunity for industrial field I/O, while MC74HC74ADTR2G offers broader temperature qualification without altering design layout or timing margins.

Availability

SN74HCS74DR is available at Aetrix Electronics and suitable for industrial pushbutton interfaces, microcontroller reset hold circuits, noise-tolerant clock division, and legacy bus signal conditioning requiring stable component supply across extended temperature ranges.

Supply support for SN74HCS74DR 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 delivering analog, embedded processing, and connectivity solutions for industrial, automotive, and consumer markets.

The SN74HCS74DR belongs to TI's HCS logic family, designed specifically for robust, low-power, wide-voltage digital interfacing in harsh electromagnetic environments.

FAQ

What is the maximum clock frequency supported by SN74HCS74DR?

The SN74HCS74DR supports a maximum switching frequency of 105 MHz at 6 V supply, as specified in the Switching Characteristics table. At 4.5 V, the max frequency drops to 95 MHz, and at 2 V it is 31 MHz. These values assume CL = 50 pF load and TA = 25°C; actual system performance may vary with trace capacitance, temperature, and supply stability. The SN74HCS74DR maintains functional operation across its full –40°C to +125°C range, though timing margins decrease at temperature extremes.

Does SN74HCS74DR require external pull-up or pull-down resistors on unused inputs?

Yes, all unused inputs on SN74HCS74DR must be terminated to either VCC or GND to prevent floating states that cause increased ICC and potential logic instability. TI recommends 10-kΩ resistors for default HIGH (pull-up) or LOW (pull-down) biasing. Unlike standard CMOS inputs, Schmitt-trigger inputs tolerate slow transitions and intermediate voltages without excessive current draw-but termination remains mandatory per datasheet Section 11.1 Layout Guidelines. Leaving inputs unconnected violates absolute maximum ratings and risks erratic behavior in the SN74HCS74DR.

Can SN74HCS74DR operate reliably with a 3.3-V supply?

Yes, SN74HCS74DR is fully specified for 3.3-V operation within its recommended 2-V to 6-V range. At 3.3 V, typical hysteresis is ΔVT ≈ 0.9 V (VT+ ≈ 2.2 V, VT− ≈ 1.3 V), propagation delay is ≤19 ns, and output drive is ±4.2 mA. Input thresholds remain well-separated from logic levels, ensuring noise margins >0.7 V. This makes SN74HCS74DR compatible with 3.3-V microcontrollers, FPGAs, and sensors without level shifters-confirming robust functionality in mixed-voltage systems using SN74HCS74DR.

How does the Schmitt-trigger input improve noise immunity in SN74HCS74DR?

The Schmitt-trigger input in SN74HCS74DR provides hysteresis (ΔVT ≥ 0.6 V at 6 V), meaning the threshold for detecting a HIGH differs from that for detecting a LOW. This prevents multiple toggles when input signals cross the threshold slowly or with superimposed noise. For example, with ΔVT = 0.8 V at 6 V, noise spikes under ±0.4 V peak-to-peak cannot trigger false transitions. This eliminates need for external RC filters in applications like pushbutton debouncing or encoder interfacing-directly enabling cleaner, more reliable signal capture in the SN74HCS74DR.

Is SN74HCS74DR pin-compatible with SN74HC74DR?

Yes, SN74HCS74DR and SN74HC74DR share identical SOIC-14 pinouts, electrical connections, and functional block diagrams. Both devices have the same terminal assignments for PRE, CLR, CLK, D, Q, Q̅, VCC, and GND. However, SN74HCS74DR substitutes Schmitt-trigger inputs for standard CMOS inputs-meaning no changes to PCB layout are needed when upgrading for noise immunity, but input signal conditioning requirements differ. This pin-for-pin compatibility simplifies redesigns where enhanced noise rejection is required in existing SN74HC74DR-based systems.