Texas Instruments SN74HC74DG4

Overview

SN74HC74DG4 from Texas Instruments is a dual D-type positive-edge-triggered flip-flop with asynchronous preset and clear inputs per channel, operating across 2 V to 6 V supply voltage and –40°C to +85°C temperature range. It delivers 39 ns max propagation delay (VCC = 6 V), supports fanout of up to 10 LSTTL loads, and is used in clock division and momentary-to-toggle switch conversion circuits.

For engineers reviewing the SN74HC74DG4 datasheet, SN74HC74DG4 pinout, SN74HC74DG4 application, or SN74HC74DG4 equivalent, this page provides verified functional mode tables, timing constraints (setup/hold/pulse width), output drive capability (±25 mA), thermal metrics (RθJA = 133.6 °C/W), and real-world implementation guidance for debounced toggle switching and divide-by-2 clock generation.

Technical Context

The SN74HC74DG4 implements two independent CMOS D-flip-flops sharing no internal logic; each has dedicated asynchronous active-low PRE and CLR pins, a single-edge-sensitive CLK input, and complementary Q/Q outputs. Its balanced push-pull outputs source/sink up to ±25 mA while maintaining VOH ≥ 5.48 V and VOL ≤ 0.33 V at VCC = 6 V and IOL = 5.2 mA.

Timing behavior is strictly defined by positive-edge clock triggering, with minimum setup time of 17 ns (VCC = 6 V), zero hold time, and pulse width requirements of 14 ns for CLK and 14 ns for PRE/CLR. Input transition rates must exceed 400 ns/V at VCC = 6 V to avoid shoot-through current and oscillation.

Key Specifications

Pinout & Package

SN74HC74DG4 uses a 14-pin SOIC (D) package with nominal body size 8.70 mm × 3.90 mm and standard JEDEC MO-002AC footprint. Thermal resistance is RθJA = 133.6 °C/W, requiring moderate PCB copper area for sustained operation at full load.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC74DG4, SN74HCT74D offers guaranteed TTL input compatibility at the cost of marginally higher static current, while MC74HC74ADG provides second-source assurance with identical functional and timing performance-both require no PCB layout changes.

Availability

SN74HC74DG4 is available at Aetrix Electronics and suitable for industrial control panels, test equipment interfaces, and consumer electronics power sequencing requiring stable component supply and long-term manufacturability.

Supply support for SN74HC74DG4 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 90 years of innovation in industrial, automotive, and communications markets.

The SN74HC74DG4 belongs to the 74HC high-speed CMOS logic family, designed specifically for low-power, pin-compatible replacements of legacy TTL devices in space-constrained and thermally sensitive applications.

FAQ

What is the maximum clock frequency supported by the SN74HC74DG4?

The SN74HC74DG4 supports a maximum clock frequency of 29 MHz at VCC = 6 V and TA = –40°C to +85°C, as specified in the Switching Characteristics table. At lower supply voltages (e.g., 4.5 V), the guaranteed maximum drops to 25 MHz. This limit derives from propagation delay (tpd ≤ 49 ns) and setup/hold timing constraints-not from internal oscillator or PLL circuitry, since SN74HC74DG4 is a purely combinational+sequential logic device with no internal clock generation.

Can unused inputs on the SN74HC74DG4 be left floating?

No, unused inputs on the SN74HC74DG4 must never be left floating. Each input exhibits high impedance and undefined voltage levels when unconnected, which can cause excessive current draw, logic oscillation, or increased EMI. Per TI's layout guidelines, all unused inputs-including 1PRE, 1CLR, 2PRE, 2CLR, 1D, 2D, 1CLK, and 2CLK-must be tied to either VCC or GND using direct connections or 10-kΩ pull-up/pull-down resistors depending on required default state.

Does the SN74HC74DG4 support mixed-voltage operation between inputs and outputs?

No, the SN74HC74DG4 does not support true mixed-voltage operation. All inputs and outputs reference the same VCC rail (2 V to 6 V). While it can interface with 3.3 V or 5 V systems via level translation, its VIH and VIL thresholds scale with VCC (e.g., VIH = 3.15 V at VCC = 4.5 V), so connecting a 5 V input to a 3.3 V-powered SN74HC74DG4 violates absolute maximum ratings and risks damage. Use SN74HCT74D for 5 V-tolerant inputs or add discrete level-shifting circuitry.

How is power dissipation calculated for the SN74HC74DG4 in dynamic operation?

Dynamic power dissipation for SN74HC74DG4 is calculated using P = Cpd × VCC² × f × N, where Cpd = 35 pF (per gate), VCC is supply voltage, f is switching frequency, and N = 2 (for both flip-flops). For example, at VCC = 5 V, f = 10 MHz, and both channels toggling, P ≈ 17.5 mW. Static power (ICC × VCC) adds <0.3 mW at VCC = 5 V. Total dissipation remains well below thermal limits in SOIC-14 unless ambient exceeds 70°C with no airflow.

What is the purpose of the NC pins on the SN74HC74DG4?

The SN74HC74DG4 (SOIC-14 package) has no NC (No Connect) pins. All 14 pins are electrically assigned: pins 1–7 and 8–14 serve as 1CLR, 1D, 1PRE, 1Q, 1Q, GND, 2Q, 2Q, 2PRE, 2D, 2CLR, VCC, 2CLK, and 1CLK respectively. NC pins appear only in the 20-pin LCCC (FK) variant, where pins 1, 5, 7, 11, 15, and 17 are internally unconnected and must remain unpopulated or grounded per layout best practices.