Part A
74AC244SCX
Fairchild Semiconductor Inc
- Lifecycle
- Active
- Stock
- 2840 PCS
- Package
- SOIC-W-20
- Series
- Logique - Buffers, lecteurs, récepteurs, émetteurs - récepteurs
Replacement verdict
Compatible functional replacement candidate
The 74AC244SCX and 74AC240SJX share the same AC-family logic, 5.5 V maximum supply, and 24 mA output drive, but they are not pin-compatible drop-in replacements: the 74AC244 is a non-inverting octal buffer with active-low enables, while the 74AC240 is an inverting octal buffer with active-high enables. The 74AC240SJX can substitute for the 74AC244SCX only when signal inversion is acceptable and the enable polarity is reworked; otherwise the 74AC244SCX remains the correct choice.
Logic Function
Validation required
Enable Polarity
Validation required
Output Drive Current
High match
Package Type
Not compatible
Parts at a glance
Part B
74AC240SJX
Semi - conducteurs
- Lifecycle
- Active
- Stock
- 7896 PCS
- Package
- SOIC-20
- Series
- Logique - Buffers, lecteurs, récepteurs, émetteurs - récepteurs
Key differences
Rows are prioritized by design impact. Highlighted values require attention during substitution.
Key electrical and mechanical differences between the two devices
| Parameter | 74AC244SCX | 74AC240SJX | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver, non-inverting, 3-state | Octal Buffer/Line Driver, inverting, 3-state | The 244 passes signals unchanged while the 240 inverts them, so they are not functionally interchangeable in a circuit without accounting for polarity. |
| Output Polarity | Non-inverting | Inverting | Polarity determines the logic state seen at the output relative to the input, directly affecting circuit behavior. |
| Number of Channels | 8 | 8 | Both devices buffer eight lines, so channel count is not a differentiator for substitutability. |
| Output Type | 3-state | 3-state | 3-state outputs allow the device to be disconnected from a bus, which is essential for shared-bus applications. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | The usable supply window must match the system rail to ensure proper logic levels and reliable operation. |
| Propagation Delay (typical) | 5.5 ns at 5 V | 5.5 ns at 5 V | Similar propagation delay means timing performance is comparable when swapping parts. |
| Output Drive Current | ±24 mA | ±24 mA | Drive strength must be sufficient for the load; matching values indicate equivalent fan-out capability. |
| Package / Mounting | SOIC-20, surface mount | SOP-20, surface mount | Package and footprint differences affect PCB layout and assembly compatibility. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | The temperature range must cover the application environment for reliable operation. |
| Logic Family | AC | AC | Same logic family ensures compatible input thresholds, noise margins, and speed characteristics. |
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 | 74AC240SJX |
|---|---|---|
| Supplier | - | onsemi |
| 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 are the main functional differences between the 74AC244SCX and the 74AC240SJX?
The 74AC244SCX is an octal buffer/line driver with non-inverting 3-state outputs, while the 74AC240SJX is an octal buffer/line driver with inverting 3-state outputs. Both are designed to drive highly capacitive or low-impedance loads, but they differ in logic polarity and pinout.
Are the 74AC244SCX and 74AC240SJX pin-to-pin compatible?
No. The 74AC244SCX and 74AC240SJX have different pin configurations. The 74AC244SCX has all inputs on one side and outputs on the opposite side, while the 74AC240SJX places inputs and outputs on opposite pins in a flow-through arrangement that differs from the '244. They are not direct drop-in replacements for each other.
What are the package types for the 74AC244SCX and 74AC240SJX?
The 74AC244SCX is supplied in a 20-lead SOIC package (SCX suffix). The 74AC240SJX is supplied in a 20-lead SOP package (SJX suffix). Both are surface-mount packages, but they have different body widths and land patterns.
Can the 74AC244SCX and 74AC240SJX be used interchangeably in a design?
No, they cannot be used interchangeably without design changes. The inverting versus non-inverting logic will invert signal polarity, and the different pinouts require PCB layout modifications. Substitution is only possible after verifying logic function, pin assignment, and timing against the target design requirements.
What are the typical operating voltage and drive current specifications for both devices?
Both the 74AC244SCX and 74AC240SJX operate over a recommended supply voltage range of 2.0 V to 6.0 V (AC family). They typically provide ±24 mA output drive at 5.0 V VCC, with symmetric source and sink currents. These parameters are consistent across the AC logic family.
Do the 74AC244SCX and 74AC240SJX have the same propagation delay and switching characteristics?
Yes, both devices are members of the 74AC family and share similar AC switching characteristics, including propagation delay, output rise/fall times, and maximum operating frequency, when tested under identical supply voltage, temperature, and load conditions. The primary difference is logic polarity, not speed.
What are the 3-state output control configurations for the 74AC244SCX and 74AC240SJX?
The 74AC244SCX has two active-low output enable pins (1OE and 2OE), each controlling four outputs. The 74AC240SJX also has two active-low output enable pins (1OE and 2OE), each controlling four outputs. In both devices, when an enable pin is high, the corresponding outputs are in a high-impedance state.
Which device is better for bus driving applications, the 74AC244SCX or the 74AC240SJX?
Both are suitable for bus driving. The choice depends on whether signal inversion is required. The 74AC244SCX provides non-inverted buffering, while the 74AC240SJX provides inverted buffering. Both offer 3-state outputs and ±24 mA drive, making them equally capable for bus interface and line driving tasks.