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 74HCT245D and 74HCT08D are not functionally interchangeable. The 74HCT245D is an octal bus transceiver with 3-state outputs and direction control, while the 74HCT08D is a quad 2-input AND gate. Their logic functions, pin configurations, and I/O characteristics differ fundamentally, so substituting one for the other is not feasible without redesigning the surrounding circuit.
Different logic function
Different channel count
Different pinout
Different output type
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HCT245D | 74HCT08D | Why it matters |
|---|---|---|---|
| Logic Function | Octal bus transceiver with 3-state outputs | Quad 2-input AND gate | Defines the core function; these devices are not functionally interchangeable as they perform entirely different logic operations. |
| Number of Channels | 8 | 4 | Determines how many independent signal lines can be processed simultaneously. |
| Direction Control | Bidirectional (DIR pin selects A-to-B or B-to-A) | Unidirectional (fixed logic inputs to output) | Affects whether the device can drive signals in both directions on a bus or only one fixed direction. |
| Output Type | 3-state (tri-state) outputs with enable control | Push-pull totem-pole outputs | 3-state outputs allow bus sharing and high-impedance isolation, while push-pull outputs cannot be tied together. |
| Output Enable / Control Pins | OE (output enable) and DIR (direction) | None (always active) | Enable pins allow the device to be disconnected from the bus, which is essential for shared-bus architectures. |
| Supply Voltage Range | 4.5 V to 5.5 V | 4.5 V to 5.5 V | Both are HCT-family devices designed for 5 V TTL-compatible systems; matching supply ranges simplifies power design. |
| Logic Family | HCT (High-speed CMOS, TTL compatible) | HCT (High-speed CMOS, TTL compatible) | Same logic family ensures compatible input thresholds and output drive characteristics. |
| Package | SOIC-20 (D suffix) | SOIC-14 (D suffix) | Different pin counts and footprints prevent direct drop-in replacement on the same PCB pad layout. |
| Propagation Delay (typical) | ~12 ns at 5 V | ~10 ns at 5 V | Affects maximum operating speed and timing margins in synchronous designs. |
| Output Drive Current | ±6 mA (standard HCT drive) | ±4 mA (standard HCT drive) | Determines fan-out capability and ability to drive loads such as LEDs or other logic inputs. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HCT08D | 74HCT245D |
|---|---|---|
| Series | 74HCT | 74HCT |
| Part Status | Obsolete | Active |
| Logic Type | AND Gate | Transceiver, Non-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 ~ 125°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 74HCT245D and the 74HCT08D?
The 74HCT245D is an octal bus transceiver with 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74HCT08D is a quad 2-input AND gate that performs logical conjunction on four independent pairs of input signals. They serve fundamentally different logic functions and are not functionally interchangeable.
Are the 74HCT245D and 74HCT08D pin-compatible in the SO14 package?
No. The 74HCT245D is typically supplied in a 20-pin package (e.g., SO20), while the 74HCT08D is supplied in a 14-pin package (e.g., SO14). The pin counts, pin assignments, and package dimensions differ, so they cannot be interchanged on the same PCB footprint.
Can the 74HCT245D and 74HCT08D operate from the same supply voltage?
Yes. Both devices are members of the 74HCT logic family and are specified for a nominal supply voltage of 5 V, with a recommended operating range typically from 4.5 V to 5.5 V. This makes them compatible with standard 5 V TTL-level systems.
Do both devices provide 3-state outputs?
No. The 74HCT245D provides 3-state outputs controlled by direction (DIR) and output enable (OE) pins, allowing the outputs to be placed in a high-impedance state. The 74HCT08D has standard push-pull outputs and does not support a high-impedance state.
What are the typical propagation delays for the 74HCT245D and 74HCT08D?
Both devices exhibit similar propagation delay characteristics as part of the HCT family. Typical propagation delay times are in the range of approximately 10 ns to 20 ns at 5 V, depending on load conditions and the specific manufacturer's datasheet. For precise values, consult the manufacturer's datasheet for each part.
Can the 74HCT245D be used to drive the inputs of the 74HCT08D?
Yes, provided the output current and voltage levels of the 74HCT245D meet the input requirements of the 74HCT08D. Both are HCT-family devices with TTL-compatible input thresholds, so the 74HCT245D can drive 74HCT08D inputs as long as the fan-out and loading limits specified in the datasheets are respected.
Are the 74HCT245D and 74HCT08D available in the same package options?
No. The 74HCT245D is commonly offered in 20-pin packages such as SO20, TSSOP20, and DIP20. The 74HCT08D is commonly offered in 14-pin packages such as SO14, TSSOP14, and DIP14. Package options differ due to the different pin counts required by each function.