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 74AC299SJX are not functionally interchangeable. The 74AC244SCX is an octal non-inverting buffer/line driver with 3-state outputs, while the 74AC299SJX is an 8-bit universal shift/storage register with 3-state outputs. They differ in logic function, pin configuration, package type, and control signal architecture, making direct substitution impossible without circuit redesign.
Different logic function
Different pin configuration
Different package type
Different control architecture
Parts at a glance
Part B
74AC299SJX
onsemi
- Lifecycle
- Active
- Stock
- 3598 PCS
- Package
- SOIC-20
- Series
- Logic - Shift Registers
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 | 74AC299SJX | Why it matters |
|---|---|---|---|
| Function | Octal Buffer/Line Driver with 3-State Outputs | 8-Bit Universal Shift/Storage Register with 3-State Outputs | These devices perform fundamentally different logic functions, so they are not functionally interchangeable in a circuit. |
| Logic Family | AC (Advanced CMOS) | AC (Advanced CMOS) | Same logic family ensures compatible voltage thresholds and switching characteristics when interfacing with other AC-family devices. |
| Number of Bits / Channels | 8 buffers (two 4-bit groups with separate enables) | 8-bit register | Channel count determines how many signal lines the device can handle, affecting bus width compatibility. |
| Output Type | 3-State | 3-State | 3-state outputs allow the device to be disconnected from a shared bus, which is essential for bus multiplexing. |
| Direction Control | Unidirectional (input to output only) | Bidirectional (shift left, shift right, or parallel load) | Direction control determines whether the device can only drive signals one way or can also shift data in both directions. |
| Supply Voltage Range | 2.0 V to 6.0 V | 2.0 V to 6.0 V | The operating voltage range must match the system supply to ensure proper logic levels and reliable operation. |
| Propagation Delay (typical) | ~5 ns at 5 V | ~7 ns at 5 V | Propagation delay affects timing margins in synchronous systems and must be compatible with clock speeds. |
| Package Type | SOIC-20 (SC suffix) | SOIC-20 (SJ suffix) | Package type and footprint must match the PCB layout for physical compatibility. |
| Operating Temperature Range | -40°C to +85°C | -40°C to +85°C | Temperature range must cover the application environment to ensure reliable operation. |
| Pin Count | 20 | 20 | Pin count affects package size and PCB footprint compatibility. |
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Full specification comparison
Use manufacturer datasheets as the final authority.
| Specification | 74AC244SCX | 74AC299SJX |
|---|---|---|
| Supplier | - | onsemi |
| Series | 74AC | 74AC |
| Part Status | Active | Obsolete |
| Logic Type | Buffer, Non-Inverting | Shift Register |
| Output Type | 3-State | Tri-State |
| Number of Elements | 2 | 1 |
| Number of Bits per Element | 4 | 8 |
| Function | - | Universal |
| Voltage - Supply | 2V ~ 6V | 2V ~ 6V |
| Operating Temperature | -40°C ~ 85°C (TA) | -40°C ~ 85°C |
| Mounting Type | Surface Mount | Surface Mount |
| Current - Output High Low | 24mA, 24mA | - |
Frequently asked questions
What are the primary functions of the 74AC244SCX and 74AC299SJX?
The 74AC244SCX is an octal buffer/line driver with 3-state outputs, designed to drive bus lines or buffer memory address registers. The 74AC299SJX is an 8-bit universal shift/storage register with 3-state outputs, capable of serial/parallel input and serial/parallel output operations.
Are the 74AC244SCX and 74AC299SJX pin-to-pin compatible?
No. The 74AC244SCX is typically offered in a 20-pin SOIC package, while the 74AC299SJX is typically offered in a 20-pin SOP package. However, their pin functions and internal architectures differ significantly, so they are not direct substitutes.
Can the 74AC244SCX be used as a drop-in replacement for the 74AC299SJX?
No. The 74AC244SCX is a non-inverting octal buffer with 3-state outputs, whereas the 74AC299SJX is a universal shift register with parallel/serial loading and storage capabilities. Their logic functions and control pin assignments are completely different.
What are the key differences in operating voltage and logic family?
Both devices belong to the AC (Advanced CMOS) logic family and typically operate over a 2.0 V to 6.0 V supply voltage range. However, their input/output characteristics, propagation delays, and drive strengths differ due to their distinct internal architectures.
Which device is better suited for bus driving applications?
The 74AC244SCX is specifically designed for bus driving and buffering, featuring 3-state outputs and high drive current. The 74AC299SJX is intended for shift register and storage applications and is not optimized for bus driving.
Do both devices support 3-state outputs?
Yes. Both the 74AC244SCX and 74AC299SJX feature 3-state outputs, allowing them to be connected to a common bus without contention when disabled.
What are the typical package options for these devices?
The 74AC244SCX is commonly available in 20-pin SOIC, TSSOP, and PDIP packages. The 74AC299SJX is commonly available in 20-pin SOP and PDIP packages. Package availability may vary by manufacturer.
Can these devices be used together in the same system?
Yes. They can be used together in a system where the 74AC299SJX performs shift/storage operations and the 74AC244SCX buffers or drives the resulting data onto a bus, provided timing and control signals are properly coordinated.