Part A
74HCT08D
東芝セミコンダクター・アンド・ストレージ
- Lifecycle
- Active
- Stock
- 6154 個数
- Package
- SOIC-14
- Series
- ロジック - ゲートおよびインバータ
Replacement verdict
Not a drop-in replacement
The 74HCT540D and 74HCT08D are not functionally interchangeable. The 74HCT540D is an octal inverting buffer/line driver with 3-state outputs, while the 74HCT08D is a quad 2-input AND gate. They differ in logic function, output type, channel count, and pinout, so substituting one for the other is not feasible without redesigning the circuit.
Different logic function
Different output type
Different channel count
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 | 74HCT08D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs (inverting) | Quad 2-input AND gate | Defines the fundamental logic operation; these devices perform completely different functions and are not functionally interchangeable. |
| Number of Channels | 8 | 4 | Determines how many independent signal paths can be processed simultaneously. |
| Output Type | 3-state | Push-pull | 3-state outputs allow bus sharing and high-impedance disconnection, while push-pull outputs cannot be tied together. |
| Logic Polarity | Inverting | Non-inverting | Affects the output state relative to the input, changing the logical behavior of the circuit. |
| Propagation Delay (tpd) | Typ. 12 ns at 5 V | Typ. 10 ns at 5 V | Impacts maximum operating frequency and timing margins in synchronous designs. |
| Output Drive Current (IOH/IOL) | ±6 mA | ±4 mA | Determines the ability to drive loads such as LEDs, other logic inputs, or transmission lines. |
| Supply Voltage Range | 4.5 V to 5.5 V | 4.5 V to 5.5 V | Defines the compatible power supply window for proper HCT logic operation. |
| Input Threshold (HCT) | TTL-compatible | TTL-compatible | Ensures direct interfacing with TTL logic levels without additional level shifting. |
| Package | SO16 (D) | SO14 (D) | Different pin counts and footprints prevent direct drop-in replacement on the same PCB pad layout. |
| Operating Temperature Range | -40 °C to +125 °C | -40 °C to +125 °C | Confirms suitability for industrial and automotive temperature environments. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT08D | 74HCT540D |
|---|---|---|
| Series | 74HCT | 74HCT |
| Part Status | Obsolete | Active |
| Logic Type | AND 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 | 18ns @ 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 74HCT08D?
The 74HCT540D is an octal inverting buffer/line driver with 3-state outputs, designed for bus-oriented applications. The 74HCT08D is a quad 2-input AND gate, used for logic gating operations. They serve fundamentally different logic functions and are not interchangeable.
Can the 74HCT540D and 74HCT08D be used interchangeably in a circuit design?
No. The 74HCT540D provides inverting buffering with 3-state output control, while the 74HCT08D performs 2-input AND logic. Their pinouts, functions, and electrical characteristics differ, so direct substitution is not possible without redesigning the circuit.
Do both the 74HCT540D and 74HCT08D operate on the same supply voltage range?
Yes. Both are HCT-family devices and typically operate with a supply voltage (VCC) of 4.5 V to 5.5 V, with 5 V being the nominal value. They are compatible with TTL input levels when used at 5 V.
What are the output drive characteristics of the 74HCT540D compared to the 74HCT08D?
The 74HCT540D is specified with symmetrical output drive of ±6 mA (at 5 V) per output, making it suitable for driving bus lines. The 74HCT08D typically provides ±4 mA output drive per gate. The 74HCT540D offers higher drive strength and 3-state capability.
How do the package and pin configurations of the 74HCT540D and 74HCT08D differ?
Both are commonly offered in SO14 (D) packages. The 74HCT540D uses a 20-pin package (e.g., SO20) because it has 8 buffer channels plus two output-enable pins. The 74HCT08D uses a 14-pin package (SO14) for four 2-input AND gates. Pin counts and assignments are not compatible.
Are the 74HCT540D and 74HCT08D both available in the same logic family and temperature range?
Yes. Both belong to the 74HCT CMOS logic family and are typically specified for the industrial temperature range of −40 °C to +125 °C (or −40 °C to +85 °C depending on manufacturer). Always verify the specific datasheet for the exact grade.
Which device is more suitable for driving a shared data bus, the 74HCT540D or the 74HCT08D?
The 74HCT540D is specifically designed for bus driving because it has 3-state outputs that can be put into high-impedance mode, allowing multiple devices to share a bus. The 74HCT08D has standard totem-pole outputs and cannot be tri-stated, so it is not suitable for direct bus connection.
Do the 74HCT540D and 74HCT08D have the same propagation delay characteristics?
No. The 74HCT540D typically has a propagation delay (tPD) of around 12–15 ns at 5 V, while the 74HCT08D typically has a tPD of around 9–12 ns. Exact values vary by manufacturer and load conditions; consult the respective datasheets for guaranteed limits.