Part A
74AC245SCX
Онсеми
- Lifecycle
- Active
- Stock
- 5851 ПКС
- Package
- SOIC-20
- Series
- Логика - буферы, драйверы, приемники, передатчики
Replacement verdict
Not a drop-in replacement
The 74AC245SCX and 74AC240SJ are not functionally interchangeable despite sharing the same AC-family logic and 20-pin SOIC footprint. The 74AC245SCX is an octal bus transceiver with non-inverting true outputs and direction control, while the 74AC240SJ is an octal buffer/line driver with inverting outputs and dual active-low output enables. The differing output polarity, control architecture, and pin function assignment prevent direct substitution without circuit redesign.
Different output polarity
Different control logic
Different pin function
Different direction architecture
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 | 74AC240SJ | 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 does not, 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; different control pin configurations require different PCB routing and logic. |
| Output Polarity | Non-inverting | Inverting | Inverting versus non-inverting outputs change the logic state of the signal, directly affecting circuit behavior and preventing direct substitution. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Defines the compatible power supply window; matching ranges allow use in the same system voltage rails. |
| Output Drive Current (IOH/IOL) | ±24 mA | ±24 mA | Determines the fan-out and ability to drive loads; identical drive strength supports similar load conditions. |
| Propagation Delay (tPD) | ~5.5 ns at 5 V | ~5.5 ns at 5 V | Affects timing margins in synchronous systems; similar delays help maintain comparable performance. |
| Package Type | SOIC-20 (SOP-20) | SOIC-20 (SOP-20) | Physical footprint and pinout must match for drop-in replacement; both share the same package but differ in pin function assignment. |
| Pin Count | 20 | 20 | Pin count affects PCB layout compatibility; identical counts ease mechanical substitution but pin functions still differ. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Ensures reliable operation across environmental conditions; matching ranges support use in similar application environments. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC245SCX | 74AC240SJ |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC,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 74AC240SJ?
The 74AC245SCX is an octal bus transceiver with non-inverting 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74AC240SJ is an octal buffer/line driver with inverting 3-state outputs, intended for unidirectional signal buffering. The 74AC245SCX provides direction control (DIR) and output enable (OE), while the 74AC240SJ provides two separate 4-bit output enable pins (1OE and 2OE) for independent control of each nibble.
Are the 74AC245SCX and 74AC240SJ pin-to-pin compatible?
No. The 74AC245SCX and 74AC240SJ have different pinouts. The 74AC245SCX uses a bidirectional transceiver pinout with A-side and B-side ports, a direction pin (DIR), and an output enable pin (OE). The 74AC240SJ uses a unidirectional buffer pinout with separate input and output pins, plus two active-low output enable pins (1OE and 2OE). They cannot be interchanged without PCB redesign.
Do the 74AC245SCX and 74AC240SJ have the same logic polarity?
No. The 74AC245SCX has non-inverting outputs, meaning the output logic state follows the input logic state. The 74AC240SJ has inverting outputs, meaning the output logic state is the inverse of the input logic state. This difference affects signal polarity and must be accounted for in any design comparison.
What are the package types for the 74AC245SCX and 74AC240SJ?
The 74AC245SCX is supplied in a 20-pin SOIC package (SC suffix indicates SOIC). The 74AC240SJ is supplied in a 20-pin SOP package (SJ suffix indicates SOP). Both are surface-mount packages with 20 pins, but they differ in package style and PCB land pattern requirements.
Can the 74AC245SCX and 74AC240SJ operate at the same supply voltage and logic levels?
Yes. Both devices are members of the AC family and are specified for operation over a 2.0 V to 6.0 V supply voltage range. They provide CMOS-compatible inputs and are characterized for AC performance at 5.0 V. However, individual datasheet limits for propagation delay, output drive, and input thresholds should be verified for the specific operating conditions.
What is the difference in output drive capability between the 74AC245SCX and 74AC240SJ?
Both devices are specified with standard AC-family output drive of ±24 mA at 5.0 V VCC. The 74AC245SCX and 74AC240SJ share similar output current specifications, but the 74AC240SJ is often characterized for balanced drive and line-driving applications. Always consult the respective manufacturer datasheets for guaranteed IOH and IOL limits over the full temperature range.
Which device is better suited for bidirectional bus applications?
The 74AC245SCX is specifically designed for bidirectional bus applications because it integrates a direction control pin (DIR) and a single output enable (OE) for the entire octal transceiver. The 74AC240SJ is a unidirectional inverting buffer and cannot perform bidirectional data transfer without external routing or additional logic.
Are the 74AC245SCX and 74AC240SJ interchangeable in an existing design?
No. They differ in logic function (non-inverting transceiver vs. inverting buffer), pinout, direction control, and output enable configuration. Direct substitution is not possible without verifying all differences against the manufacturer datasheets and validating the target design requirements.