Part A
74AC244SCX
飛兆電晶體公司
- Lifecycle
- Active
- Stock
- 2840 件
- Package
- SOIC-W-20
- Series
- 邏輯-緩衝器、驅動器、接收器、收發器
Replacement verdict
Not a drop-in replacement
The 74AC244SCX and 74AC257SC are not functionally interchangeable. The 74AC244SCX is an octal non-inverting buffer/line driver with 3-state outputs, while the 74AC257SC is a quad 2-input multiplexer with 3-state outputs. They differ in logic function, channel count, input/output configuration, and pinout, so the 74AC257SC cannot directly replace the 74AC244SCX in existing designs without circuit redesign.
Different logic function
Different channel count
Different input configuration
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 | 74AC244SCX | 74AC257SC | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver with 3-state outputs | Quad 2-input Multiplexer with 3-state outputs | The core function differs fundamentally; one buffers signals while the other selects between two data inputs, so they are not functionally interchangeable. |
| Number of Channels | 8 | 4 | Channel count determines how many independent signal paths can be handled, affecting board layout and I/O capacity. |
| Input Type | Single-ended (one input per channel) | Two inputs per channel (multiplexed) | The multiplexer requires two data inputs per channel plus a select line, while the buffer needs only one, changing pinout and wiring requirements. |
| Output Type | 3-state | 3-state | Both offer 3-state outputs, but the control logic differs: the buffer uses output-enable pins, while the multiplexer uses select and enable pins. |
| Control Inputs | Two output-enable (OE) pins | One select (S) pin and one output-enable (OE) pin | Different control schemes mean the driving logic and timing must be redesigned when substituting one for the other. |
| Propagation Delay (typical) | ~5.5 ns at 5 V | ~6.5 ns at 5 V | Timing differences can affect setup/hold margins and maximum operating frequency in synchronous designs. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both support the same AC-family voltage range, so power supply compatibility is not a differentiator. |
| Package | SOIC-20 (SOP-20) | SOIC-16 (SOP-16) | Different package sizes and pin counts prevent direct drop-in replacement on an existing PCB footprint. |
| Pin Count | 20 | 16 | Pin count mismatch means the two parts cannot share the same socket or land pattern. |
| Output Drive Current | ±24 mA at 5 V | ±24 mA at 5 V | Equivalent drive strength means both can interface with similar loads, but the functional difference still prevents direct substitution. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC244SCX | 74AC257SC |
|---|---|---|
| Supplier | - | onsemi |
| Series | 74AC | 74AC |
| Part Status | Active | Obsolete |
| Type | - | Multiplexer |
| Circuit | - | 4 x 2:1 |
| Independent Circuits | - | 1 |
| Current - Output High Low | 24mA, 24mA | 24mA, 24mA |
| Voltage Supply Source | - | Single Supply |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C (TA) | -40°C ~ 85°C |
| 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 functions of the 74AC244SCX and 74AC257SC?
The 74AC244SCX is an octal buffer/line driver with 3-state outputs, designed to drive high-capacitance loads or backplanes. The 74AC257SC is a quad 2-input multiplexer with 3-state outputs, used to select between two data sources.
Are the 74AC244SCX and 74AC257SC pin-compatible?
No. The 74AC244SCX is a 20-pin device with a different pinout than the 74AC257SC, which is a 16-pin device. They are not pin-to-pin replacements.
Can the 74AC244SCX and 74AC257SC operate at the same supply voltage?
Yes. Both devices are members of the AC family and typically operate over a 2.0 V to 6.0 V VCC range, with 5.0 V being the most common supply for standard logic applications.
What is the difference in output drive capability between the 74AC244SCX and 74AC257SC?
The 74AC244SCX provides standard AC-family output drive of ±24 mA at 5.0 V VCC. The 74AC257SC also provides ±24 mA at 5.0 V VCC, so their drive strengths are equivalent under the same conditions.
Do both the 74AC244SCX and 74AC257SC have 3-state outputs?
Yes. The 74AC244SCX has 3-state outputs controlled by two active-low output-enable pins. The 74AC257SC has 3-state outputs controlled by a single active-low output-enable pin.
Which device is better for multiplexing two data buses?
The 74AC257SC is specifically designed as a quad 2-input multiplexer and is the appropriate choice for selecting between two 4-bit data sources. The 74AC244SCX is a buffer/driver and does not perform multiplexing.
Are the 74AC244SCX and 74AC257SC available in the same package type?
Both devices are offered in SOIC packages, but the 74AC244SCX is a 20-pin SOIC while the 74AC257SC is a 16-pin SOIC. Package footprint and pin count differ.
Can the 74AC244SCX be used to replace the 74AC257SC in an existing design?
No. The devices have different logic functions, pin counts, and pinouts. A direct replacement is not possible without redesigning the circuit and PCB layout.