Part A
74AC245SCX
Онсеми
- Lifecycle
- Active
- Stock
- 5851 ПКС
- Package
- SOIC-20
- Series
- Логика - буферы, драйверы, приемники, передатчики
Replacement verdict
Compatible functional replacement candidate
The 74AC245SCX and 74AC240TTR share the same AC-family CMOS technology, 5 V supply range, and 24 mA output drive, but they are not pin-to-pin equivalent: the 74AC245SCX is an octal bus transceiver with non-inverting true outputs and direction control, while the 74AC240TTR is an octal buffer/line driver with inverting outputs and dual active-low output enables. The 74AC240TTR can serve as a functional substitute only when output inversion is acceptable and the board layout is redesigned for the differing enable and pinout configuration.
Logic Function
Validation required
Output Type
Not compatible
Supply Voltage
High match
Pin Configuration
Validation required
Parts at a glance
Part B
74AC240TTR
STМикроэлектроника
- Lifecycle
- Active
- Stock
- 5772 ПКС
- Package
- TSSOP-20
- Series
- Логика - буферы, драйверы, приемники, передатчики
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 | 74AC240TTR | 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 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 245 uses a single direction pin while the 240 uses two output-enable pins, changing the control logic required. |
| Output Polarity | Non-inverting | Inverting | Polarity determines whether the output signal matches or is inverted relative to the input, which is critical for signal integrity and logic compatibility. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Defines the operating voltage window; both parts share the same AC-family range, allowing use in similar power rails. |
| Output Drive Current (IOH/IOL) | ±24 mA | ±24 mA | Determines the load-driving capability; identical drive strength means either can drive similar loads. |
| Propagation Delay (tPD) | ~5.5 ns at 5 V | ~5.5 ns at 5 V | Affects maximum operating frequency and timing margins; matching delays simplify timing analysis when substituting. |
| Package Type | SOIC-20 (SOP-20) | TSSOP-20 | Footprint and thermal characteristics differ; TSSOP is smaller than SOIC, so PCB layout compatibility must be verified. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Ensures reliable operation across environmental conditions; identical ranges mean both suit the same application environments. |
| Logic Family | AC (Advanced CMOS) | AC (Advanced CMOS) | Same logic family ensures compatible input thresholds, noise margins, and interfacing with other AC-family devices. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC245SCX | 74AC240TTR |
|---|---|---|
| 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 74AC240TTR?
The 74AC245SCX is an octal bus transceiver with non-inverting 3-state outputs, designed for bidirectional asynchronous communication between data buses. The 74AC240TTR is an octal buffer/line driver with inverting 3-state outputs, intended for unidirectional signal buffering. The key differences are the 74AC245SCX's bidirectional capability and non-inverting outputs versus the 74AC240TTR's unidirectional, inverting outputs.
Are the 74AC245SCX and 74AC240TTR pin-to-pin compatible?
No. The 74AC245SCX and 74AC240TTR have different pinouts. The 74AC245SCX uses a direction control (DIR) and output enable (OE) pin to manage bidirectional data flow, while the 74AC240TTR uses two separate active-low output enable pins (1OE and 2OE) for its two 4-bit inverting buffer sections. Therefore, they are not direct drop-in replacements.
Can the 74AC245SCX be used as a direct substitute for the 74AC240TTR in an existing design?
No, a direct substitution is not possible without design changes. The 74AC245SCX is a bidirectional transceiver with non-inverting outputs, whereas the 74AC240TTR is a unidirectional inverting buffer. Using the 74AC245SCX in place of the 74AC240TTR would require reversing the signal logic (due to inversion) and reconfiguring the direction control pins, which is not a pin-compatible or functionally equivalent replacement.
What are the package types for the 74AC245SCX and 74AC240TTR?
The 74AC245SCX is typically offered in a 20-pin SOIC package (SCX suffix indicates SOIC packaging for the 74AC245). The 74AC240TTR is typically offered in a 20-pin TSSOP package (TTR suffix indicates TSSOP packaging for the 74AC240). Both are surface-mount packages, but they have different physical dimensions and PCB land patterns.
Do the 74AC245SCX and 74AC240TTR have the same output drive current?
Both devices are part of the AC family and typically feature balanced output drive of ±24 mA at 5 V VCC, as specified in their respective manufacturer datasheets. However, always verify the exact drive current from the specific manufacturer's datasheet for the ordered part number, as slight variations may exist between vendors.
What is the function of the direction control pin on the 74AC245SCX compared to the 74AC240TTR?
The 74AC245SCX has a Direction (DIR) pin that selects whether data flows from the A bus to the B bus or from the B bus to the A bus. The 74AC240TTR does not have a direction control pin because it is a unidirectional device; its two 4-bit sections are permanently configured as inputs on one side and outputs on the other, controlled only by output enable pins.
Are the 74AC245SCX and 74AC240TTR interchangeable in terms of logic polarity?
No. The 74AC245SCX provides non-inverting outputs, meaning the output logic state matches the input logic state. The 74AC240TTR provides inverting outputs, meaning the output logic state is the opposite of the input logic state. This fundamental difference prevents direct interchangeability without accounting for signal inversion.
Which device is better suited for bidirectional bus applications?
The 74AC245SCX is specifically designed for bidirectional bus applications due to its transceiver architecture with direction control and 3-state outputs. The 74AC240TTR is not suitable for bidirectional bus applications because it is a unidirectional inverting buffer/line driver with no direction control capability.