Part A
74HC238D
도시바 반도체 및 스토리지
- Lifecycle
- Active
- Stock
- 5394 PCS
- Package
- SOIC-16
- Series
- 논리 - 신호 스위치, 멀티플렉서, 디코더
Replacement verdict
Not a drop-in replacement
The 74HC244D and 74HC238D are not functionally interchangeable despite sharing the same 74HC logic family and SOIC-16 package. The 74HC244D is an octal non-inverting buffer/line driver with 3-state outputs, while the 74HC238D is a 3-to-8 line decoder/demultiplexer with active-high outputs. Their internal logic functions, pin assignments, and signal flow are fundamentally different, so substituting one for the other in an existing design is not feasible without redesigning the surrounding circuitry.
Different logic function
Different output type
Different pin assignment
Different channel count
Parts at a glance
Part B
74HC244D
도시바 반도체 및 스토리지
- Lifecycle
- Active
- Stock
- 7745 PCS
- Package
- SOIC-20
- Series
- 논리 - 버퍼, 드라이브, 수신기, 트랜시버
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74HC244D | 74HC238D | Why it matters |
|---|---|---|---|
| Logic Function | Octal buffer/line driver with 3-state outputs | 3-to-8 line decoder/demultiplexer | The core function differs fundamentally; one buffers signals while the other decodes addresses, so they are not functionally interchangeable. |
| Number of Outputs | 8 | 8 | Both provide eight outputs, but the output activation logic differs (buffered data vs. one-of-eight decoded selection). |
| Output Type | 3-state | Active-low (non-3-state) | 3-state outputs allow bus sharing, while the decoder's standard outputs cannot be tri-stated, affecting bus interfacing. |
| Control Inputs | Two active-low output enable pins (1OE, 2OE) | Three enable inputs (two active-low, one active-high) | Different enable schemes change how the device is gated and cascaded in a system. |
| Input Configuration | 8 data inputs | 3 address inputs | The number and role of inputs determine the device's application; buffering uses parallel data, decoding uses binary address lines. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both operate over the standard HC-family supply range, so power compatibility is identical. |
| Logic Family | 74HC (high-speed CMOS) | 74HC (high-speed CMOS) | Same logic family ensures comparable input thresholds, noise margins, and drive characteristics. |
| Package | SO14 (D suffix) | SO16 (D suffix) | 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 | Identical temperature ratings mean both suit the same industrial and automotive environments. |
| Propagation Delay (typical at 5 V) | ~11 ns | ~14 ns | Timing differences affect signal integrity and maximum operating frequency in synchronous designs. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74HC238D | 74HC244D |
|---|---|---|
| Series | 74HC | 74HC |
| Part Status | Active | Active |
| Type | Decoder/Demultiplexer | - |
| Circuit | 1 x 3:8 | - |
| Independent Circuits | 1 | - |
| Current - Output High Low | 5.2mA, 5.2mA | 7.8mA, 7.8mA |
| Voltage Supply Source | Single Supply | - |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 125°C | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
| Logic Type | - | Buffer, Non-Inverting |
| Number of Elements | - | 2 |
| Number of Bits per Element | - | 4 |
| Output Type | - | 3-State |
Frequently asked questions
What are the primary functional differences between the 74HC244D and the 74HC238D?
The 74HC244D is an octal non-inverting buffer/line driver with 3-state outputs, designed for signal buffering and bus driving. The 74HC238D is a 3-to-8 line decoder/demultiplexer that decodes three binary select inputs into eight mutually exclusive active-HIGH outputs. They serve fundamentally different logic functions and are not interchangeable.
Can the 74HC244D and 74HC238D be used together in the same circuit?
Yes. A common configuration uses the 74HC238D to decode a 3-bit address into eight active-HIGH select lines, while the 74HC244D buffers or drives the resulting signals or data bus. Their functions are complementary rather than conflicting.
Do the 74HC244D and 74HC238D have the same pin count and package?
Both devices are typically offered in a 16-pin SOIC package (the "D" suffix in Nexperia nomenclature denotes SOIC-16). However, pin assignments differ because the internal functions differ. The 74HC244D uses pins for eight data inputs, eight 3-state outputs, and two active-LOW output enable pins. The 74HC238D uses pins for three select inputs, three enable inputs, and eight decoded outputs.
What are the output drive capabilities of the 74HC244D and 74HC238D?
Both devices are members of the 74HC family and typically provide standard CMOS output drive of ±4 mA at 5 V VCC per output, as specified in manufacturer datasheets. The 74HC244D is intended for bus driving with 3-state outputs, while the 74HC238D provides standard push-pull decoded outputs.
What is the difference in output enable control between the two devices?
The 74HC244D has two active-LOW output enable pins (1OE and 2OE) that independently control the 3-state condition of the two 4-bit output groups. The 74HC238D has three enable inputs (two active-LOW and one active-HIGH) that must all be in their active state for any output to be active; otherwise all eight outputs are forced LOW.
Are the 74HC244D and 74HC238D compatible with 3.3 V logic systems?
Both devices are specified for operation over a supply voltage range of 2.0 V to 6.0 V, which includes 3.3 V. At 3.3 V VCC, both are compatible with 3.3 V logic levels. However, input thresholds and output drive strength should be verified against the specific manufacturer datasheet for the target operating voltage.
Which device is suitable for driving a shared data bus?
The 74HC244D is suitable for driving a shared data bus because its 3-state outputs allow the device to be placed in a high-impedance state, effectively disconnecting from the bus when not selected. The 74HC238D does not have 3-state outputs and is not intended for direct bus driving; it is a decoder/demultiplexer.
What are the typical propagation delays for the 74HC244D and 74HC238D?
At 5 V VCC and 25 °C, the 74HC244D typically exhibits a propagation delay of approximately 11 ns to 15 ns from input to output, depending on the manufacturer. The 74HC238D typically exhibits a propagation delay of approximately 14 ns to 20 ns from select or enable input to output. Exact values vary by manufacturer and should be confirmed from the specific datasheet.