Part A
74AC244SCX
Fairchild Semiconductor
- Lifecycle
- Active
- Stock
- 2840 PCS
- Package
- SOIC-W-20
- Series
- Logic - Buffers, Drivers, Receivers, Transceivers
Replacement verdict
Compatible functional replacement candidate
The 74AC240SC and 74AC244SCX are functionally compatible octal buffer/driver devices from the same AC logic family, sharing identical supply voltage ranges, drive current, propagation delays, and SOIC-20 package footprints. The primary distinction is the 74AC240SC's inverting outputs versus the 74AC244SCX's non-inverting outputs, which must be accounted for in signal polarity. Both devices are suitable as functional replacement candidates where output polarity requirements are satisfied.
Output Polarity
Validation required
Logic Family
High match
Package Type
High match
Supply Voltage Range
High match
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74AC240SC | 74AC244SCX | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver with 3-state outputs, inverting | Octal Buffer/Line Driver with 3-state outputs, non-inverting | The inverting vs non-inverting behavior fundamentally changes signal polarity, so the parts are not functionally interchangeable in a circuit. |
| Number of Channels | 8 | 8 | Channel count must match to preserve the number of signals that can be buffered or driven. |
| Output Type | 3-state | 3-state | 3-state outputs allow the device to be disconnected from a bus, which is essential for shared-bus architectures. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | The operating voltage range must be compatible with the system power rail for reliable operation. |
| Output Drive Current | ±24 mA | ±24 mA | Drive current determines the load the buffer can reliably drive, affecting fan-out and signal integrity. |
| Propagation Delay | ~5.5 ns at 5 V | ~5.5 ns at 5 V | Propagation delay affects timing margins in synchronous systems and must be within design limits. |
| Package Type | SOIC-20 | SOIC-20 | Package must match the PCB footprint for physical compatibility and assembly. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Temperature range must cover the application environment to ensure reliable operation. |
| Input Type | CMOS | CMOS | CMOS inputs provide high impedance and low static power, which affects interfacing with other logic families. |
Need help validating a replacement?
Send your BOM and application constraints for technical and sourcing review.
Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC244SCX | 74AC240SC |
|---|---|---|
| Series | 74AC | 74AC |
| Part Status | Active | Obsolete |
| Logic Type | Buffer, Non-Inverting | Buffer, Inverting |
| Number of Elements | 2 | 2 |
| Number of Bits per Element | 4 | 4 |
| 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 is the main functional difference between the 74AC240SC and the 74AC244SCX?
The 74AC240SC is an octal buffer/line driver with 3-state outputs that includes inverting outputs, while the 74AC244SCX is an octal buffer/line driver with 3-state outputs that has non-inverting outputs. Both are designed to drive highly capacitive or relatively low-impedance loads.
Are the 74AC240SC and 74AC244SCX pin-compatible?
Yes, both devices are typically offered in the same 20-pin package configurations (such as SOIC) and share the same pinout for power, ground, enable, and data pins. However, the logic polarity of the corresponding data outputs differs due to the inverting versus non-inverting function.
Can the 74AC240SC be used as a direct drop-in replacement for the 74AC244SCX?
No, they are not direct drop-in replacements because the 74AC240SC provides inverted outputs while the 74AC244SCX provides non-inverted outputs. Substitution requires a design review to account for the logic polarity change.
What are the typical operating voltage and logic family characteristics of these devices?
Both the 74AC240SC and 74AC244SCX belong to the AC (Advanced CMOS) logic family and typically operate over a supply voltage range of 2.0 V to 6.0 V, with balanced output drive and propagation delays suitable for high-speed applications.
Do both devices feature 3-state outputs?
Yes, both the 74AC240SC and 74AC244SCX include 3-state outputs controlled by two active-low output enable pins (often labeled 1OE and 2OE), allowing the outputs to be placed in a high-impedance state for bus-oriented applications.
What is the difference in output current drive capability between the two parts?
Both devices are specified with similar output drive characteristics within the AC logic family, typically capable of sourcing and sinking symmetrical currents (e.g., ±24 mA at 5 V VCC) as defined in their respective manufacturer datasheets. Always verify the exact drive ratings from the specific manufacturer datasheet.
Which device is better for non-inverting bus buffering applications?
The 74AC244SCX is the appropriate choice for non-inverting bus buffering because its outputs follow the logic level of the corresponding inputs. The 74AC240SC would invert the signal, which may be undesirable unless inversion is explicitly required.
Are the 74AC240SC and 74AC244SCX available in the same package types?
Both devices are commonly available in similar package options, including SOIC, TSSOP, and sometimes PDIP, depending on the manufacturer. Package availability can vary by supplier, so consult the specific product ordering information for each part number.