Part A
74AC245SCX
onsemi
- Lifecycle
- Active
- Stock
- 5851 PCS
- Package
- SOIC-20
- Series
- Lógica - Buffers, Drivers, Receivers, Transceivers
Replacement verdict
Compatible functional replacement candidate
The 74AC245SCX and 74AC240MTR are both 20-pin AC-series octal bus interface devices with comparable supply voltage, temperature, and package characteristics, but they differ in logic function and pinout. The 74AC245SCX is an octal bus transceiver with non-inverting 3-state outputs, while the 74AC240MTR is an octal buffer/line driver with inverting 3-state outputs. Because the 74AC240MTR inverts the signal and has a different pin configuration, it is not a direct drop-in replacement for the 74AC245SCX; however, it can serve as a functional substitute in applications where signal inversion is acceptable and the board layout is adjusted accordingly.
Logic Function
Validation required
Output Type
Not compatible
Package Type
High match
Supply Voltage
High match
Parts at a glance
Part B
74AC240MTR
STMicroeletrônica
- Lifecycle
- Active
- Stock
- 5987 PCS
- Package
- SOIC-20
- Series
- Lógica - Buffers, Drivers, Receivers, Transceivers
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74AC245SCX | 74AC240MTR | Why it matters |
|---|---|---|---|
| Logic Function | Octal Bus Transceiver (non-inverting, 3-state) | Octal Buffer/Line Driver (inverting, 3-state) | Determines the direction and polarity of signal flow; a transceiver supports bidirectional data transfer while an inverting buffer only drives one direction with inverted outputs, so they are not functionally interchangeable. |
| Number of Direction Control Pins | 1 (DIR pin selects A-to-B or B-to-A) | 2 (1OE and 2OE, each controlling 4 channels) | Affects how the device is enabled and controlled in a circuit; the transceiver uses a single direction pin while the buffer uses separate output-enable pins for two 4-bit groups. |
| Output Polarity | Non-inverting | Inverting | Inverting outputs change the logic state of the signal, which would require additional inversion stages if used as a drop-in replacement for a non-inverting device. |
| Channel Configuration | 8 channels, all controlled together | 8 channels split into two 4-bit groups | Determines whether the eight channels can be enabled independently; the 74AC240 allows separate control of two 4-bit halves, while the 74AC245 controls all eight together. |
| Package / Mounting | SOIC-20 (surface mount) | SOIC-20 (surface mount) | Both share the same 20-pin SOIC footprint, so PCB layout compatibility is maintained even though the internal logic differs. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Both operate over the standard AC-family supply range, allowing use in 3.3 V and 5 V systems without level shifting. |
| Output Drive Current (IOH/IOL) | ±24 mA | ±24 mA | Identical drive strength means both can source and sink the same load current, which is important for driving buses and capacitive lines. |
| Propagation Delay (tPD) | ~5.5 ns at 5 V | ~5.5 ns at 5 V | Similar propagation delay ensures comparable timing performance in high-speed digital systems. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Both meet industrial temperature requirements, making them suitable for the same environmental conditions. |
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Send your BOM and application constraints for technical and sourcing review.
Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC245SCX | 74AC240MTR |
|---|---|---|
| Supplier | - | STMicroelectronics |
| Series | 74AC | 74AC |
| Part Status | Active | Obsolete |
| Logic Type | Transceiver, Non-Inverting | Buffer, Inverting |
| Number of Elements | 1 | 2 |
| Number of Bits per Element | 8 | 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) | -55°C ~ 125°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the primary functional differences between the 74AC245SCX and the 74AC240MTR?
The 74AC245SCX is an octal bus transceiver with non-inverting 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74AC240MTR is an octal buffer/line driver with inverting 3-state outputs, intended for unidirectional data flow. The key differences are the 245's bidirectional capability and non-inverting outputs versus the 240's unidirectional, inverting outputs.
Are the 74AC245SCX and 74AC240MTR pin-to-pin compatible?
No. The 74AC245SCX and 74AC240MTR have different pinouts. The 74AC245SCX uses a direction control (DIR) pin and an output enable (OE) pin, while the 74AC240MTR uses two active-low output enable pins (1OE and 2OE) and has inverting outputs. Their pin functions and control logic differ, so they are not direct drop-in replacements.
Can the 74AC245SCX be used as a direct substitute for the 74AC240MTR in an existing design?
No. Direct substitution is not possible without design changes. The 74AC245SCX is a bidirectional non-inverting transceiver, while the 74AC240MTR is a unidirectional inverting buffer. Signal polarity, direction control, and pin assignments differ, so replacing one with the other would require schematic and PCB modifications.
What are the package types for the 74AC245SCX and 74AC240MTR?
The 74AC245SCX is typically offered in a 20-pin SOIC package (SC suffix indicates SOIC). The 74AC240MTR is typically offered in a 20-pin SOIC package as well (MTR suffix indicates tape and reel, SOIC). Both are surface-mount 20-pin devices, but their pinouts and functions differ.
What are the operating voltage and logic family specifications for these devices?
Both the 74AC245SCX and 74AC240MTR belong to the AC (Advanced CMOS) logic family. They typically operate over a supply voltage range of 2.0 V to 6.0 V, with characterized operation at 5.0 V. They provide balanced output drive and are compatible with TTL voltage levels when operated at 5.0 V.
What is the difference in output drive current between the 74AC245SCX and 74AC240MTR?
Both devices are from the 74AC family and typically provide ±24 mA output drive current at 5.0 V supply. The drive strength is similar, but the 74AC240MTR inverts the signal, while the 74AC245SCX does not. Always verify the specific manufacturer datasheet for exact IOH/IOL ratings, as they can vary slightly between vendors.
Which device is better for bidirectional bus applications?
The 74AC245SCX is the appropriate choice for bidirectional bus applications because it is designed as an octal bus transceiver with direction control. The 74AC240MTR is a unidirectional inverting buffer and cannot handle bidirectional data flow without external logic to manage direction.
Do both devices feature 3-state outputs?
Yes. Both the 74AC245SCX and the 74AC240MTR have 3-state outputs, allowing them to be placed in a high-impedance state for bus sharing. The 74AC245SCX uses an output enable (OE) pin to control the high-impedance state, while the 74AC240MTR uses two output enable pins (1OE and 2OE) to control its two 4-bit sections independently.