Part A
74AC244SCX
Công ty bán dẫn Fairchild
- Lifecycle
- Active
- Stock
- 2840 PCS
- Package
- SOIC-W-20
- Series
- Logic - Buffers, Drivers, Receivers, Transceivers
Replacement verdict
Not a drop-in replacement
The 74AC244SCX and 74AC240SCX are not functionally interchangeable despite sharing the same AC-family SOIC-20 package and similar electrical characteristics. The 74AC244SCX provides non-inverting true outputs, whereas the 74AC240SCX provides inverting outputs, making them logically incompatible for direct substitution. Additionally, the 74AC240SCX integrates a 3-state output enable function that is not present on the 74AC244SCX, further preventing a drop-in replacement without circuit redesign.
Different output polarity
Different enable logic
Different logic function
Different pin function
Parts at a glance
Part B
74AC240SCX
Công ty bán dẫn Fairchild
- Lifecycle
- Active
- Stock
- 9919 PCS
- Package
- SOIC-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 | 74AC244SCX | 74AC240SCX | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver, non-inverting | Octal Buffer/Line Driver, inverting | Determines output polarity; a non-inverting buffer passes the signal unchanged while an inverting buffer flips the logic level, so they are not directly interchangeable in a circuit. |
| Output Enable Polarity | Active-LOW (OE1, OE2) | Active-LOW (OE1, OE2) | Both devices use active-LOW output enables, so the control logic for enabling/disabling outputs is compatible between the two parts. |
| Number of Channels | 8 | 8 | Both provide eight buffer channels, so the pin count and channel capacity are identical for bus-driving applications. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | Identical operating voltage range means both can be used in the same 3.3 V or 5 V systems without level-shifting concerns. |
| Output Drive Current | ±24 mA | ±24 mA | Matching drive strength ensures equivalent fan-out and signal integrity when driving capacitive or resistive loads. |
| Propagation Delay | ~5.5 ns (at 5 V) | ~5.5 ns (at 5 V) | Similar propagation delay means timing characteristics are essentially the same, so swapping parts will not significantly affect system timing. |
| Package Type | SOIC-20 | SOIC-20 | Identical package and pinout allow direct PCB footprint compatibility, simplifying substitution. |
| Operating Temperature Range | -40 °C to +85 °C | -40 °C to +85 °C | Same temperature range ensures both parts are suitable for the same industrial and commercial environments. |
| Input Type | CMOS | CMOS | CMOS inputs provide high impedance and low static current, making both compatible with similar logic families. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC244SCX | 74AC240SCX |
|---|---|---|
| Supplier | - | Rochester Electronics, LLC |
| Series | 74AC | 74AC |
| Part Status | Active | Active |
| 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 is the main functional difference between the 74AC244SCX and the 74AC240SCX?
The 74AC244SCX is an octal buffer/line driver with non-inverting 3-state outputs, while the 74AC240SCX is an octal buffer/line driver with inverting 3-state outputs. Both are designed to drive highly capacitive or relatively low-impedance loads.
Are the 74AC244SCX and 74AC240SCX pin-compatible?
Yes, both devices are offered in the same 20-pin SOIC package (SCX suffix) and share the same pinout. The 74AC244SCX and 74AC240SCX have identical pin assignments for inputs, outputs, and enable pins, but the logic polarity of the outputs differs.
Can the 74AC244SCX be used as a direct drop-in replacement for the 74AC240SCX?
No, they are not direct drop-in replacements because the 74AC244SCX has non-inverting outputs and the 74AC240SCX has inverting outputs. Substitution requires a design review to account for the logic polarity inversion, which may affect signal phase and system timing.
What are the output drive characteristics of the 74AC244SCX and 74AC240SCX?
Both devices are members of the AC family and typically provide ±24 mA output drive at 5 V VCC, with balanced propagation delays and symmetrical output impedance. They are specified for driving transmission lines and capacitive loads.
What is the operating voltage range for the 74AC244SCX and 74AC240SCX?
Both devices operate over a recommended supply voltage range of 2.0 V to 6.0 V, with characteristics specified at 3.3 V, 5.0 V, and other intermediate voltages within the AC family ratings.
How do the 3-state enable controls differ between the 74AC244SCX and 74AC240SCX?
Both devices feature two active-low output enable pins (1OE and 2OE) that control the four outputs in each half of the device. When an enable pin is high, the corresponding outputs are placed in a high-impedance state. The enable logic is identical for both parts.
What are the typical propagation delay and operating temperature ranges for these devices?
At 5 V VCC and 25°C, typical propagation delays are approximately 5 ns to 7 ns for both the 74AC244SCX and 74AC240SCX. The operating temperature range for the SCX suffix is typically -40°C to +85°C, as specified in manufacturer datasheets.
Which applications typically use the 74AC244SCX versus the 74AC240SCX?
The 74AC244SCX is commonly used for non-inverting buffering, clock distribution, and memory address driving. The 74AC240SCX is used where signal inversion is required, such as in inverting bus drivers, signal conditioning, and interface circuits needing active-low logic conversion.