Part A
74AC244SCX
Компания Fairchild Semiconductor
- Lifecycle
- Active
- Stock
- 2840 ПКС
- Package
- SOIC-W-20
- Series
- Логика - буферы, драйверы, приемники, передатчики
Replacement verdict
Not a drop-in replacement
The 74AC244SCX and 74AC20SCX are not functionally interchangeable. The 74AC244SCX is an octal buffer/line driver with 3-state outputs, while the 74AC20SCX is a dual 4-input NAND gate. They differ in logic function, channel count, output type, and pin configuration, making direct substitution impossible without circuit redesign.
Different logic function
Different channel count
Different output type
Different pin configuration
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 | 74AC20SCX | Why it matters |
|---|---|---|---|
| Logic Function | Octal Buffer/Line Driver with 3-State Outputs | Dual 4-Input NAND Gate | These are fundamentally different logic functions, so they are not functionally substitutable in a circuit. |
| Number of Channels | 8 | 2 | Channel count determines how many independent signal paths the device can handle. |
| Input Type | Single-ended | Single-ended | Input type affects compatibility with upstream logic levels and interfacing requirements. |
| Output Type | 3-State | Push-Pull | 3-state outputs allow bus sharing, while push-pull outputs cannot be tied together without contention. |
| Supply Voltage Range | 2 V to 6 V | 2 V to 6 V | The supply voltage range must match the system rail to ensure proper operation and logic level compatibility. |
| Propagation Delay | ~5.5 ns at 5 V | ~7 ns at 5 V | Propagation delay affects maximum operating frequency and timing margins in synchronous designs. |
| Output Drive Current | ±24 mA | ±24 mA | Drive current determines the ability to drive loads such as LEDs, transmission lines, or other logic inputs. |
| Package Type | SOIC-20 | SOIC-14 | Package footprint and pin count must match the PCB layout for physical 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. |
| Pin Count | 20 | 14 | Pin count affects board layout, routing, and whether the part can be dropped into an existing footprint. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC244SCX | 74AC20SCX |
|---|---|---|
| Supplier | - | onsemi |
| Series | 74AC | 74AC |
| Part Status | Active | Obsolete |
| Logic Type | Buffer, Non-Inverting | NAND Gate |
| Number of Circuits | - | 2 |
| Number of Inputs | - | 4 |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Current - Quiescent (Max) | - | 2 µA |
| Current - Output High Low | 24mA, 24mA | 24mA, 24mA |
| Logic Level - Low | - | 0.9V ~ 1.65V |
| Logic Level - High | - | 2.1V ~ 3.85V |
| Max Propagation Delay @ V Max CL | - | 7ns @ 5V, 50pF |
| Operating Temperature | -40°C ~ 85°C (TA) | -40°C ~ 85°C |
| Mounting Type | Surface Mount | Surface Mount |
| Number of Elements | 2 | - |
| Number of Bits per Element | 4 | - |
| Output Type | 3-State | - |
Frequently asked questions
What are the primary functional differences between the 74AC244SCX and the 74AC20SCX?
The 74AC244SCX is an octal buffer/line driver with 3-state outputs, designed for driving bus lines or buffering memory address registers. The 74AC20SCX is a dual 4-input NAND gate, designed for logic gating operations. They serve fundamentally different logic functions and are not pin-to-pin or function-to-function replacements.
Are the 74AC244SCX and 74AC20SCX pin-compatible?
No. The 74AC244SCX is typically supplied in a 20-pin SOIC package (SCX suffix), while the 74AC20SCX is typically supplied in a 14-pin SOIC package. They have different pin counts, pin assignments, and package footprints, so they cannot be interchanged on the same PCB land pattern.
Can the 74AC244SCX and 74AC20SCX operate from the same power supply voltage?
Yes. Both devices are members of the AC family and are specified for operation over a recommended supply voltage range of 2.0 V to 6.0 V. However, AC family devices are typically characterized for 5 V operation, and timing parameters vary with supply voltage.
What is the output drive capability of the 74AC244SCX compared to the 74AC20SCX?
The 74AC244SCX is specified with ±24 mA output drive at 5 V VCC, making it suitable for bus driving and line driving applications. The 74AC20SCX has standard AC family output drive, typically ±24 mA at 5 V VCC as well, but its NAND gate output structure is intended for logic signal propagation rather than bus driving. Actual drive levels should be confirmed on the specific manufacturer datasheet.
Do both devices have 3-state outputs?
No. The 74AC244SCX features 3-state outputs controlled by two active-low output enable pins (1OE and 2OE), allowing the outputs to be placed in a high-impedance state. The 74AC20SCX has standard push-pull totem-pole outputs with no 3-state capability.
What are the typical propagation delays for these devices?
At 5 V VCC and 25°C, the 74AC244SCX typically exhibits propagation delays in the range of approximately 3 ns to 7 ns depending on the manufacturer and load conditions. The 74AC20SCX typically exhibits propagation delays in the range of approximately 3 ns to 8 ns under similar conditions. Exact values vary by manufacturer and must be verified on the specific datasheet.
Are the 74AC244SCX and 74AC20SCX interchangeable in a design?
No. Because they implement different logic functions (octal 3-state buffer vs. dual 4-input NAND gate), have different pin counts, and different package footprints, they are not interchangeable. Substitution would require a complete redesign of the surrounding circuit and PCB layout.
What logic family do the 74AC244SCX and 74AC20SCX belong to?
Both devices belong to the 74AC (Advanced CMOS) logic family. This family is known for high-speed operation, CMOS-level input thresholds, and balanced output drive, and is generally compatible with 5 V TTL logic levels when operated at 5 V VCC.