Part A
74HCT02D
Toshiba Semiconductor and Storage
- Lifecycle
- Active
- Stock
- 5658 PCS
- Package
- SOIC-16
- Series
- Logic - Gates and Inverters
Replacement verdict
Not a drop-in replacement
The 74HCT540D and 74HCT02D are not functionally interchangeable. The 74HCT540D is an octal inverting buffer/line driver with 3-state outputs, while the 74HCT02D is a quad 2-input NOR gate. Their logic functions, channel counts, output configurations, and pin assignments differ fundamentally, making direct substitution impossible without redesigning the surrounding circuit.
Different logic function
Different channel count
Different output type
Different pinout
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HCT540D | 74HCT02D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs (inverting) | Quad 2-input NOR gate | The core logic function determines whether the devices are functionally interchangeable; these are fundamentally different functions and cannot substitute for each other. |
| Number of Gates / Channels | 8 buffers (octal) | 4 NOR gates | Channel count affects how many signals can be processed and how the device maps into a given circuit design. |
| Output Type | 3-state (tri-state) outputs | Standard push-pull (totem-pole) outputs | 3-state outputs allow bus sharing and high-impedance disconnection, while push-pull outputs cannot be tied together on a shared bus. |
| Input Configuration | Single input per channel with output enable pins (OE1, OE2) | Two inputs per gate | Input topology determines the logic operation performed and the pin-level wiring required in the target circuit. |
| Propagation Delay (tpd, typical) | Approximately 12 ns at 5 V | Approximately 9 ns at 5 V | Propagation delay affects timing margins and maximum operating frequency in synchronous and timing-critical designs. |
| Output Drive Current (IOH/IOL) | ±6 mA (standard HCT drive) | ±4 mA (standard HCT drive) | Drive current determines fan-out capability and the ability to drive loads such as LEDs, long traces, or multiple inputs. |
| Pin Count / Package | 20-pin SOIC (D package) | 14-pin SOIC (D package) | Package and pin count must match the PCB footprint; different pin counts mean the devices are not drop-in compatible. |
| Supply Voltage Range (VCC) | 4.5 V to 5.5 V | 4.5 V to 5.5 V | Both operate over the standard HCT 5 V range, so supply compatibility is not a differentiator here. |
| Input Threshold Compatibility | TTL-compatible inputs (HCT family) | TTL-compatible inputs (HCT family) | TTL-compatible thresholds allow direct interfacing with 5 V TTL logic levels without additional level shifting. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Both cover the industrial temperature range, so thermal environment is not a limiting factor for substitution. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT02D | 74HCT540D |
|---|---|---|
| Series | 74HCT | 74HCT |
| Part Status | Obsolete | Active |
| Logic Type | NOR Gate | Buffer, Inverting |
| Number of Circuits | 4 | - |
| Number of Inputs | 2 | - |
| Voltage - Supply | 4.5V ~ 5.5V | 4.5V ~ 5.5V |
| Current - Quiescent (Max) | 1 µA | - |
| Current - Output High Low | 4mA, 4mA | 6mA, 6mA |
| Logic Level - Low | 0.8V | - |
| Logic Level - High | 2V | - |
| Max Propagation Delay @ V Max CL | 16ns @ 5.5V, 50pF | - |
| Operating Temperature | -40°C ~ 85°C | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Elements | - | 1 |
| Number of Bits per Element | - | 8 |
| Output Type | - | 3-State |
Frequently asked questions
What are the primary functional differences between the 74HCT540D and the 74HCT02D?
The 74HCT540D is an octal inverting buffer/line driver with 3-state outputs, designed for bus-oriented applications. The 74HCT02D is a quad 2-input NOR gate, providing four independent logic gates. They serve fundamentally different logic functions and are not functionally interchangeable.
Are the 74HCT540D and 74HCT02D pin-compatible?
No. The 74HCT540D is typically supplied in a 20-pin package (e.g., SO20), while the 74HCT02D is typically supplied in a 14-pin package (e.g., SO14). The pin counts, pin assignments, and package footprints differ, so they cannot be used as drop-in replacements for each other.
Do both devices operate from the same supply voltage range?
Yes. Both the 74HCT540D and 74HCT02D are HCT-family devices and operate from a nominal 5 V supply, with a specified operating range of 4.5 V to 5.5 V per standard 74HCT specifications.
Can the 74HCT540D drive a bus while the 74HCT02D performs logic gating in the same design?
Yes. Because they perform different functions, they can coexist in the same system. The 74HCT540D can drive or buffer bus lines with its 3-state outputs, while the 74HCT02D can implement NOR logic elsewhere in the circuit. Their compatibility depends on shared logic-level and supply-voltage requirements, not on functional equivalence.
What is the output drive capability of the 74HCT540D compared with the 74HCT02D?
The 74HCT540D is specified with standard 74HCT output drive, typically ±6 mA at 5 V, and is intended for bus driving. The 74HCT02D is a standard logic gate with similar 74HCT output drive characteristics, typically ±4 mA to ±6 mA depending on the manufacturer and test conditions. Exact values should be verified from the specific manufacturer datasheet.
Does the 74HCT540D have 3-state outputs while the 74HCT02D does not?
Yes. The 74HCT540D features 3-state outputs controlled by two active-low output-enable pins, allowing high-impedance bus disconnection. The 74HCT02D has standard push-pull outputs and no 3-state capability.
Are both devices available in SO14 or SO20 surface-mount packages?
The 74HCT540D is commonly offered in a 20-pin SO package (SO20), while the 74HCT02D is commonly offered in a 14-pin SO package (SO14). Package options may vary by manufacturer, so the exact package suffix should be confirmed from the manufacturer datasheet or authorized distributor listing.
Can the 74HCT02D be used to replace the 74HCT540D in a bus-driving application?
No. The 74HCT02D is a quad 2-input NOR gate with push-pull outputs and cannot provide the 3-state bus-driving function of the 74HCT540D. Replacing one with the other would require a complete redesign of the logic and bus interface.