Part A
74AC245SCX
onsemi
- Lifecycle
- Active
- Stock
- 5851 PCS
- Package
- SOIC-20
- Series
- Logic - Buffers, Drivers, Receivers, Transceivers
Replacement verdict
Compatible functional replacement candidate
The 74AC245SCX and 74AC240MTC are both 20-pin AC-series octal bus interface devices sharing identical supply voltage, logic family, and temperature ratings, but they differ in direction control and pinout. The 74AC245SCX is a bidirectional transceiver with a single direction pin, while the 74AC240MTC is a unidirectional inverting buffer with dual enable pins. Direct substitution requires careful attention to signal direction, polarity, and PCB layout.
Logic Family
High match
Supply Voltage
High match
Output Type
Validation required
Pin Configuration
Not compatible
Parts at a glance
Part B
74AC240MTC
onsemi
- Lifecycle
- Active
- Stock
- 6321 PCS
- Package
- TSSOP-20
- Series
- Logic - 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 | 74AC240MTC | 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 | Polarity determines whether the output signal matches or is complemented relative to the input, directly impacting logic-level compatibility in a target design. |
| Logic Family | AC (Advanced CMOS) | AC (Advanced CMOS) | Same logic family ensures comparable input thresholds, noise margins, and drive characteristics, which is essential for substitutability. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Defines the operating voltage window; matching ranges allow the parts to be used in the same power environment. |
| Output Drive Current (IOH/IOL) | ±24 mA | ±24 mA | Determines the load-driving capability; identical drive strength means either part can drive similar loads. |
| Propagation Delay (tPD) | ~5.5 ns at 5 V | ~5.5 ns at 5 V | Affects timing in high-speed circuits; similar delays mean comparable performance in timing-critical paths. |
| Package Type | SOIC-20 (SOP-20) | TSSOP-20 | Package footprint and thermal characteristics differ; a board layout designed for one package may not accept the other without modification. |
| Pin Count | 20 | 20 | Same pin count but different pinout assignments; pin-to-pin compatibility must be verified before substitution. |
| Pinout Configuration | A0-A7, B0-B7, DIR, OE | 1A1-1A4, 1Y1-1Y4, 2A1-2A4, 2Y1-2Y4, 1OE, 2OE | Different pin assignments mean the devices are not drop-in replacements even though both are 20-pin parts. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC245SCX | 74AC240MTC |
|---|---|---|
| Supplier | - | onsemi |
| 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) | -40°C ~ 85°C (TA) |
| Mounting Type | Surface Mount | Surface Mount |
Frequently asked questions
What are the primary functional differences between the 74AC245SCX and the 74AC240MTC?
The 74AC245SCX is an octal bus transceiver with non-inverting 3-state outputs, designed for bidirectional asynchronous communication between two data buses. The 74AC240MTC is an octal buffer/line driver with inverting 3-state outputs, intended for unidirectional data flow. The 74AC245SCX provides direction control (DIR) and output enable (OE), while the 74AC240MTC provides two separate 4-bit output enable pins (1OE and 2OE) for independent control of each nibble.
Are the 74AC245SCX and 74AC240MTC pin-to-pin compatible?
No. The 74AC245SCX and 74AC240MTC have different pin functions and internal signal routing. The 74AC245SCX uses pins for A-port data, B-port data, direction control, and output enable. The 74AC240MTC uses pins for input data, inverted output data, and two separate output enable signals. They are not direct drop-in replacements for each other.
Can the 74AC245SCX be used as a direct substitute for the 74AC240MTC in an existing design?
No. The 74AC245SCX is a non-inverting bidirectional transceiver, while the 74AC240MTC is an inverting unidirectional buffer. Substitution would require logic inversion, different control signal mapping, and verification of bidirectional versus unidirectional data flow. A direct substitution is not possible without redesigning the surrounding circuitry.
What are the package differences between the 74AC245SCX and the 74AC240MTC?
The 74AC245SCX is supplied in a 20-pin SOIC package (SCX suffix typically denotes SOIC). The 74AC240MTC is supplied in a 20-pin TSSOP package (MTC suffix typically denotes TSSOP). The package footprint, land pattern, and thermal characteristics differ, so PCB layout changes are required when switching between them.
Do both devices operate at the same supply voltage and logic levels?
Yes. Both the 74AC245SCX and 74AC240MTC are AC-family CMOS devices. They typically operate over a supply voltage range of 2.0 V to 6.0 V and provide standard AC-family input and output voltage thresholds. However, always verify the specific datasheet for the exact recommended operating conditions and DC electrical characteristics.
What is the difference in output drive current between the 74AC245SCX and the 74AC240MTC?
Both devices are AC-family octal buffers/drivers and typically provide symmetrical output drive of ±24 mA at 5.0 V VCC. The output drive specification is generally the same for both devices within the same logic family and package type. Confirm the exact IOH/IOL ratings from the respective manufacturer datasheets.
Which device is better for bidirectional bus applications?
The 74AC245SCX is specifically designed for bidirectional bus applications because it includes direction control and non-inverting 3-state outputs on both ports. The 74AC240MTC is intended for unidirectional buffering and cannot directly support bidirectional data flow without external logic or additional transceivers.
Are the control input structures the same on both devices?
No. The 74AC245SCX has a direction control (DIR) pin and a single output enable (OE) pin. The 74AC240MTC has two output enable pins (1OE and 2OE) that independently control the two 4-bit sections, but it has no direction control pin. The control logic and truth tables are therefore different.
Can both devices be used in the same application without level shifting?
Yes, provided both devices are operated within the same AC-family supply voltage and logic level range. Since both are 74AC series devices, they use compatible input and output voltage thresholds when powered from the same VCC. No level shifting is required between them under matched supply conditions.