Part A
74HCT14D
Toshiba Semiconductor và lưu trữ
- Lifecycle
- Active
- Stock
- 6342 PCS
- Package
- SOIC-14
- Series
- Logic - Gates and Inverters
Replacement verdict
Not a drop-in replacement
The 74HCT14D and 74HCT7403D,518 are not functionally interchangeable. The 74HCT14D is a hex inverting Schmitt-trigger device, while the 74HCT7403D,518 is a quad 2-input NAND buffer with open-drain outputs. They differ in logic function, channel count, output configuration, and input threshold behavior, so direct substitution is not possible without circuit redesign.
Different logic function
Different channel count
Different output type
Different input threshold
Parts at a glance
Part B
74HCT7403D,518
NXP Hoa Kỳ Inc.
- Lifecycle
- Active
- Stock
- 3207 PCS
- Package
- SOIC-16
- Series
- Logic - FIFOs Memory
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HCT14D | 74HCT7403D,518 | Why it matters |
|---|---|---|---|
| Logic Function | Hex Inverting Schmitt Trigger | Quad 2-Input NAND Gate (Open-Drain) | The logic function determines the boolean operation performed; these are fundamentally different functions and are not functionally substitutable. |
| Number of Gates/Channels | 6 | 4 | The number of independent gates affects how many signals can be processed in a single package. |
| Number of Inputs per Gate | 1 | 2 | Input count per gate determines the logic capability and wiring requirements of each gate. |
| Output Type | Push-Pull (Totem-Pole) | Open-Drain | Open-drain outputs require external pull-up resistors and allow wired-OR configurations, while push-pull outputs drive both high and low actively. |
| Input Type | Schmitt Trigger | Standard CMOS/TTL-compatible | Schmitt trigger inputs provide hysteresis for noise immunity and slow signal handling, which standard inputs do not offer. |
| Supply Voltage Range | 4.5 V to 5.5 V | 4.5 V to 5.5 V | The supply voltage range must match the system power rail for proper operation and logic level compatibility. |
| Logic Family | HCT (High-Speed CMOS, TTL-compatible) | HCT (High-Speed CMOS, TTL-compatible) | The logic family determines input threshold compatibility and switching characteristics with other logic devices. |
| Propagation Delay (typical) | ~19 ns at 5 V | ~15 ns at 5 V | Propagation delay affects maximum operating frequency and timing margins in synchronous designs. |
| Package Type | SO-14 (Small Outline) | SO-14 (Small Outline) | Package type and pin count must match the PCB footprint for physical compatibility. |
| Pin Count | 14 | 14 | Pin count must match the board layout; however, identical pin count does not guarantee identical pinout or function. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT14D | 74HCT7403D,518 |
|---|---|---|
| Supplier | - | NXP USA Inc. |
| Series | 74HCT | 74HCT |
| Part Status | Active | Obsolete |
| Memory Size | - | 256 (64 x 4) |
| Function | - | Asynchronous, Synchronous |
| Data Rate | - | 30MHz |
| Access Time | - | 61ns |
| Voltage - Supply | 4.5V ~ 5.5V | 4.5 V ~ 5.5 V |
| Current - Supply (Max) | - | 1mA |
| Bus Directional | - | Uni-Directional |
| Expansion Type | - | Depth, Width |
| Programmable Flags Support | - | No |
| Retransmit Capability | - | No |
| FWFT Support | - | No |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 125°C |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | Inverter | - |
| Number of Circuits | 6 | - |
| Number of Inputs | 1 | - |
| Features | Schmitt Trigger | - |
| Current - Quiescent (Max) | 1 µA | - |
| Current - Output High Low | 4mA, 4mA | - |
| Max Propagation Delay @ V Max CL | 31ns @ 5.5V, 50pF | - |
Frequently asked questions
What are the primary functional differences between the 74HCT14D and the 74HCT7403D,518?
The 74HCT14D is a hex inverting Schmitt trigger, providing six independent inverter channels with hysteresis for noise immunity and signal conditioning. The 74HCT7403D,518 is a quad 2-input NAND buffer with open-drain outputs, designed for wired-OR logic and driving higher current loads. They serve fundamentally different logic and signal-conditioning functions.
Can the 74HCT14D and 74HCT7403D,518 be used interchangeably in a circuit design?
No. The 74HCT14D provides inverting Schmitt trigger functions, while the 74HCT7403D,518 provides quad 2-input NAND open-drain outputs. Their logic functions, output structures, and pinouts differ, so they are not pin-to-pin or function-to-function replacements.
What are the output drive characteristics of the 74HCT7403D,518 compared to the 74HCT14D?
The 74HCT7403D,518 features open-drain outputs, which can sink current but cannot source current, typically rated for higher sink currents to drive LEDs or wired-OR buses. The 74HCT14D has standard push-pull CMOS outputs that both source and sink current, with symmetrical drive characteristics suitable for general logic interfacing.
Do both devices operate at the same supply voltage and logic levels?
Yes. Both the 74HCT14D and 74HCT7403D,518 are HCT-family devices, operating from a 4.5 V to 5.5 V supply with TTL-compatible input thresholds. They are designed for 5 V systems and can interface with TTL logic levels while providing CMOS-compatible outputs.
What is the significance of the Schmitt trigger inputs in the 74HCT14D?
The 74HCT14D includes Schmitt trigger inputs with defined positive and negative threshold voltages, providing hysteresis. This makes it suitable for slow or noisy input signals, debouncing mechanical switches, and converting analog-like waveforms into clean digital outputs. The 74HCT7403D,518 does not have Schmitt trigger inputs.
Are the package and pin configurations of the 74HCT14D and 74HCT7403D,518 compatible?
Both devices are typically offered in SO14 packages, but their pin functions differ. The 74HCT14D uses a standard hex inverter pinout, while the 74HCT7403D,518 uses a quad 2-input NAND pinout with open-drain outputs. Therefore, they are not pin-compatible despite similar package sizes.
Which device is better suited for driving LEDs or wired-OR logic?
The 74HCT7403D,518 is better suited for driving LEDs or wired-OR logic because its open-drain outputs can sink current and be tied together to form a common node. The 74HCT14D is not intended for wired-OR configurations due to its push-pull outputs.
Can the 74HCT14D be used to clean up noisy signals before feeding the 74HCT7403D,518?
Yes. The 74HCT14D can condition noisy or slow-rising input signals using its Schmitt trigger hysteresis, producing clean digital levels. The cleaned output can then drive inputs of the 74HCT7403D,518 for further logic processing or open-drain output driving.