Part A
74AC244SCX
フェアチャイルドセミコンダクター
- Lifecycle
- Active
- Stock
- 2840 個数
- Package
- SOIC-W-20
- Series
- ロジック - バッファ、ドライバ、レシーバ、トランシーバ
Replacement verdict
Not a drop-in replacement
The 74AC244SCX and 74AC245SC are not functionally interchangeable. The 74AC244SCX is a unidirectional octal buffer with dual active-low output enables, while the 74AC245SC is a bidirectional octal bus transceiver with direction control and a single active-low output enable. Their pin functions, control logic, and I/O behavior differ fundamentally, so substituting one for the other requires circuit redesign and cannot be treated as a drop-in replacement.
Different I/O direction
Different control logic
Different enable configuration
Different pin function assignment
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 | 74AC245SC | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver, non-inverting, with 3-state outputs | Octal Bus Transceiver, non-inverting, with 3-state outputs | Determines the directionality of the device; the '244 is unidirectional while the '245 supports bidirectional data flow, which is critical for bus applications. |
| Direction Control | Two output-enable (OE) pins, one per 4-bit group | Direction (DIR) pin plus output-enable (OE) pin | The '245 can reverse data direction on the fly, whereas the '244 has fixed direction, affecting circuit design flexibility. |
| Number of Channels | 8 | 8 | Both devices handle the same number of signal lines, so bus width compatibility is identical. |
| Output Type | 3-state | 3-state | 3-state outputs allow the device to be disconnected from the bus, enabling shared bus architectures. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Compatible operating voltage ranges ensure both parts can be used in the same power environment. |
| Logic Family | AC | AC | Same logic family means similar speed, drive strength, and input/output characteristics. |
| Package | SOIC-20 | SOIC-20 | Identical package and pin count allow for drop-in PCB footprint compatibility. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Same temperature range ensures both parts are suitable for industrial-grade applications. |
| Output Drive Current | ±24 mA | ±24 mA | Equal drive strength means both can drive similar loads without additional buffering. |
| Propagation Delay | ~5.5 ns at 5 V | ~5.5 ns at 5 V | Similar propagation delay ensures timing compatibility in high-speed designs. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC244SCX | 74AC245SC |
|---|---|---|
| Supplier | - | onsemi |
| Series | 74AC | 74AC |
| Part Status | Active | Obsolete |
| Logic Type | Buffer, Non-Inverting | Transceiver, Non-Inverting |
| Number of Elements | 2 | 1 |
| Number of Bits per Element | 4 | 8 |
| Output Type | 3-State | 3-State |
| Current - Output High Low | 24mA, 24mA | 24mA, 24mA |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C (TA) | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the primary functional differences between the 74AC244SCX and the 74AC245SC?
The 74AC244SCX is an octal buffer/line driver with 3-state outputs, featuring two active-low output enable pins (1OE and 2OE) that control four outputs each. The 74AC245SC is an octal bus transceiver with 3-state outputs, featuring a direction control pin (DIR) and an output enable pin (OE), allowing bidirectional data flow between two buses. Both are 20-pin SOIC devices from the AC family.
Are the 74AC244SCX and 74AC245SC pin-compatible?
No. Although both are 20-pin SOIC packages, their pin functions differ. The 74AC244SCX uses pins 1 and 19 as active-low output enables, with all 8 channels unidirectional (A to Y). The 74AC245SC uses pin 1 as DIR (direction control) and pin 19 as OE (active-low output enable), with 8 channels arranged as bidirectional A-to-B or B-to-A ports. Direct PCB substitution without layout changes is not possible.
Can the 74AC244SCX be used as a drop-in replacement for the 74AC245SC in an existing design?
No. The 74AC245SC requires a direction control signal (DIR) and has bidirectional bus ports, while the 74AC244SCX has two independent output enable pins and unidirectional inputs and outputs. Pin functions, control logic, and signal flow differ, so a direct drop-in replacement is not feasible without circuit redesign.
What are the key AC switching characteristics of these devices?
Both devices are members of the 74AC family, which typically features propagation delays in the range of approximately 3 ns to 8 ns at 5 V VCC and 25°C, depending on load conditions and supply voltage. For verified and guaranteed limits, refer to the respective manufacturer datasheets (e.g., Texas Instruments or ON Semiconductor) for the 74AC244 and 74AC245.
What is the difference in control logic between the 74AC244SCX and the 74AC245SC?
The 74AC244SCX has two active-low output enable pins: 1OE controls outputs 1Y through 4Y, and 2OE controls outputs 5Y through 8Y. When an OE pin is high, the corresponding outputs are in high-impedance state. The 74AC245SC has one active-low output enable (OE) that controls all 8 channels, and a direction pin (DIR) that selects data flow from A to B (DIR high) or B to A (DIR low). When OE is high, both ports are in high-impedance state.
Are the 74AC244SCX and 74AC245SC available in the same package type?
Yes, both the 74AC244SCX and the 74AC245SC are offered in 20-pin SOIC (Small Outline Integrated Circuit) packages. The "SCX" suffix on the 74AC244SCX typically denotes tape and reel packaging from ON Semiconductor (now onsemi), while the 74AC245SC is also a 20-pin SOIC device. However, pinouts differ as noted above.
What are the recommended operating conditions for these devices?
Both the 74AC244SCX and 74AC245SC are specified for operation over a supply voltage range of 2.0 V to 6.0 V, with 5.0 V being the nominal VCC. Operating temperature range is typically -40°C to +85°C for industrial-grade versions. For exact limits and derating information, consult the official manufacturer datasheet.
Which device should be chosen for unidirectional bus buffering versus bidirectional bus interfacing?
For unidirectional bus buffering or line driving, the 74AC244SCX is appropriate because it provides eight unidirectional channels with independent output enable control. For bidirectional bus interfacing between two buses, the 74AC245SC is the correct choice because it supports direction control and bidirectional data flow. Selection depends on whether the application requires one-way or two-way signal transmission.