SN74HCT74 - Dual D-Type Flip-Flop with Clear/Preset | TI
MPN： SN74HCT74 ✓ 啟用中SN74HCT74 概覽
A D-type flip-flop is a fundamental sequential logic element that stores one bit of data. On the rising edge of the clock signal, the output (Q) takes the value of the data input (D). The SN74HCT74 contains two independent flip-flops, each with preset (PRE) and clear (CLR) inputs that asynchronously set or reset the outputs regardless of clock state. This makes it essential for building registers, counters, and state machines in digital systems.
Key features include a wide operating voltage range of 4.5V to 5.5V, low power consumption with a maximum ICC of 40 µA, and the ability to drive up to 10 LSTTL loads. The typical propagation delay (tpd) is 15 ns at 5V, and the output drive capability is ±4 mA. The device is fully specified for operation from -40°C to 85°C, making it suitable for industrial applications.
The SN74HCT74 uses HCT (High-Speed CMOS with TTL-compatible inputs) technology, which combines the low power of CMOS with the input thresholds of TTL. This allows direct interfacing with TTL logic without additional level shifting. The positive-edge-triggered design ensures reliable data capture, and the asynchronous preset and clear inputs provide flexible control for initialization and reset operations.
Typical applications include data storage registers, frequency dividers, and control logic in microcontrollers, industrial automation, and consumer electronics. The device is also used in debouncing circuits and as a building block for more complex sequential logic. Its TTL compatibility makes it ideal for mixed-voltage systems.
When designing with the SN74HCT74, ensure that the setup and hold times are met relative to the clock edge. The preset and clear inputs are active-low and should be tied high when unused. Decouple the power supply with a 0.1 µF capacitor near the VCC pin to minimize noise.
直接替換替代品，適用於 SN74HCT74 — 相同封裝，腳位對腳位相容。需重新設計 PCB 的不同封裝零件不列入。
SN74HCT74N
✅ 直接替換📋 參考替代品（不在目錄中）
SN74HCT74D
✅ 直接替換📋 參考替代品（不在目錄中）
SN74HCT74PW
✅ 直接替換📋 參考替代品（不在目錄中）
CD74HCT74E
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
MC74HCT74AN
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
74HCT74D
✅ 直接替換 ⚠️ 規格未經驗證📋 參考替代品（不在目錄中）
SN74HCT74 最大額定值與電氣特性
| Number of Channels | 2 |
| Logic Family | HCT |
| Logic Type | D-Type Flip-Flop |
| Trigger Type | Positive Edge |
| 輸出類型 | Complementary |
| Supply Voltage - Min | 4.5 V |
| Supply Voltage - Max | 5.5 V |
| Maximum Quiescent Current | 40 µA |
| Propagation Delay Time | 15 ns (typical at 5V) |
| Output Current | ±4 mA |
| Input Type | TTL-Compatible |
| 工作溫度範圍 | -40°C to +85°C |
| Package Type | 14-DIP (N), 14-SOIC (D), 14-TSSOP (PW) |
| 安裝方式 | Through Hole / SMD |
| RoHS 狀態 | Compliant |
SN74HCT74 腳位配置
| 腳位 1 | 1CLR — Clear input for flip-flop 1 (active low) |
| 腳位 2 | 1D — Data input for flip-flop 1 |
| 腳位 3 | 1CLK — Clock input for flip-flop 1 (positive edge) |
| 腳位 4 | 1PRE — Preset input for flip-flop 1 (active low) |
| 腳位 5 | 1Q — Output Q for flip-flop 1 |
| 腳位 6 | 1Q̅ — Complementary output for flip-flop 1 |
| 腳位 7 | GND — Ground |
| 腳位 8 | 2Q̅ — Complementary output for flip-flop 2 |
| 腳位 9 | 2Q — Output Q for flip-flop 2 |
| 腳位 10 | 2PRE — Preset input for flip-flop 2 (active low) |
| 腳位 11 | 2CLK — Clock input for flip-flop 2 (positive edge) |
| 腳位 12 | 2D — Data input for flip-flop 2 |
| 腳位 13 | 2CLR — Clear input for flip-flop 2 (active low) |
| 腳位 14 | VCC — Positive supply voltage (4.5V to 5.5V) |
典型應用
SN74HCT74 適用於 6 應用s: Data Storage Registers, Frequency Dividers, Control Logic in Microcontrollers, Industrial Automation, Consumer Electronics, Test and Measurement Equipment.
Data Storage Registers
The SN74HCT74 is used to build data storage registers in digital systems. Its dual flip-flops can store two bits of data, and the positive-edge triggering ensures synchronous operation with the system clock. The clear and preset inputs allow initialization to known states, which is critical for register-based state machines. With a propagation delay of 15 ns, it supports clock frequencies up to 66 MHz, making it suitable for moderate-speed data paths. The TTL-compatible inputs simplify interfacing with legacy TTL logic, and the low quiescent current of 40 µA minimizes power consumption in battery-powered devices.
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Frequency Dividers
The SN74HCT74 can be configured as a frequency divider by connecting the Q output to the D input, creating a toggle flip-flop. Each flip-flop divides the clock frequency by two, and cascading two flip-flops provides a divide-by-4 function. The positive-edge triggering ensures clean division with minimal skew. The device's 5V operation and TTL compatibility make it ideal for dividing clocks in mixed-logic systems. The typical propagation delay of 15 ns limits the maximum input frequency to about 66 MHz, which is adequate for many microcontroller and FPGA applications. The clear input can be used to reset the divider to a known state.
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Control Logic in Microcontrollers
The SN74HCT74 is used in microcontroller systems for debouncing switches, generating interrupts, and implementing simple state machines. Its TTL-compatible inputs allow direct connection to microcontroller I/O pins without level shifting. The preset and clear inputs provide asynchronous control for resetting or setting flags. The low power consumption (40 µA max ICC) is beneficial for portable and battery-operated devices. The device operates from 4.5V to 5.5V, matching typical microcontroller supply voltages. The 15 ns propagation delay ensures fast response for control signals, and the ±4 mA output drive can directly drive LEDs or other loads.
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Industrial Automation
In industrial automation, the SN74HCT74 is used for sequence control, interlocking, and alarm logic. Its robust operating temperature range (-40°C to +85°C) and 5V operation make it suitable for harsh environments. The clear and preset inputs allow fail-safe initialization of control logic. The TTL-compatible inputs interface directly with industrial sensors and PLCs. The low quiescent current reduces heat dissipation in control cabinets. The device's dual flip-flop configuration saves board space and reduces component count. The 15 ns propagation delay ensures timely response in high-speed automation lines.
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Consumer Electronics
The SN74HCT74 is used in consumer electronics for remote control decoding, display multiplexing, and user interface logic. Its small package options (SOIC, TSSOP) enable compact PCB designs. The 5V operation is compatible with common consumer ICs. The low power consumption extends battery life in portable devices. The positive-edge triggering ensures reliable data capture in noisy environments. The preset and clear inputs allow resetting the device to a known state during power-up. The device's cost-effectiveness makes it ideal for high-volume consumer products.
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Test and Measurement Equipment
The SN74HCT74 is used in test and measurement equipment for signal conditioning, event counting, and timing generation. Its precise positive-edge triggering ensures accurate event capture. The TTL-compatible inputs interface with various test probes and sensors. The wide operating temperature range allows use in benchtop and field instruments. The low propagation delay (15 ns) enables high-speed counting. The clear input allows resetting counters to zero. The device's dual flip-flop configuration can be used to build frequency counters and time-interval meters.
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推薦產品摘要
工程參考資料，適用於 SN74HCT74 — 比較、設計指引及合規資訊。
選型指南
與替代品比較
| 參數 | 本產品 | SN74HCT74N | CD74HCT74E | MC74HCT74AN |
|---|---|---|---|---|
| Package | 14-DIP (N), 14-SOIC (D), 14-TSSOP (PW) | 14-DIP (N) | 14-DIP (N) | 14-DIP (N) |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | onsemi |
| Supply Voltage Range | 4.5V to 5.5V | 4.5V to 5.5V | 4.5V to 5.5V | 4.5V to 5.5V |
| Propagation Delay (typ) | 15 ns | 15 ns | 15 ns | 15 ns |
| Max Quiescent Current | 40 µA | 40 µA | 40 µA | 40 µA |
| Output Drive | ±4 mA | ±4 mA | ±4 mA | ±4 mA |
| Operating Temperature | -40°C to +85°C | -40°C to +85°C | -40°C to +85°C | -40°C to +85°C |
| Input Type | TTL-Compatible | TTL-Compatible | TTL-Compatible | TTL-Compatible |
主要差異化特點
- TTL-compatible inputs (對比SN74HC74)
- Multiple package options (對比CD74HCT74E)
- Low power consumption (對比74HCT74D (NXP))
設計說明
Decouple the VCC pin with a 0.1 µF ceramic capacitor placed as close to the pin as possible. For noisy environments, add a 10 µF electrolytic capacitor in parallel. The SN74HCT74 operates from 4.5V to 5.5V, so ensure the supply is within this range to avoid undefined logic states.
For high-speed operation, keep traces short and avoid long parallel runs to reduce crosstalk. Use a solid ground plane to minimize noise. The 14-pin DIP package is through-hole, while SOIC and TSSOP are surface-mount; adjust pad sizes accordingly. Ensure adequate clearance for the active-low preset and clear inputs.
Unused preset and clear inputs must be tied high to VCC to prevent false triggering. The setup and hold times must be met relative to the clock edge; refer to the datasheet for specific values. Do not exceed the absolute maximum ratings, especially on input voltages, to avoid damage.
合規資訊
RoHS compliant per TI product page. Not AEC-Q100 qualified for automotive.
