74AC521SJ

Overview

The Fairchild Semiconductor 74AC521SJ is an expandable 8-bit identity comparator housed in a 20-lead Small Outline Package (SOP). It compares two 8-bit words and provides a LOW output when the inputs are identical. The device operates within a supply voltage range of 2.0V to 6.0V, with typical propagation delays of 13ns at 5V. It features buffered clock inputs for timing control and supports bus-oriented applications through its logic structure.

Feature Summary

• Performs 8-bit identity comparison between two parallel data words
• Provides active-low output signal indicating input equality
• Expandable architecture allows cascading for wider bit comparisons
• Buffered inputs ensure clean signal transitions

Applications

• Digital system data validation
• Memory address matching circuits
• Parallel data verification modules
• Control logic equality checks

Procurement Notes

Verify the manufacturer origin as Fairchild Semiconductor or acquired entities like onsemi. Confirm the package type is 20-SOIC with 5.3mm width. Check RoHS compliance status if required by project specifications. Ensure the part number suffix SJ matches the specific lead-free and tape-and-reel or tube packaging variant intended for assembly.

Selection Notes

Select this component for applications requiring precise 8-bit equality detection. Consider the AC series speed and power characteristics relative to standard TTL requirements. Evaluate the SOP-20 footprint compatibility with existing PCB layouts. Verify that the expandable nature meets future scalability needs without redesigning the core comparison logic.

Part Context

This component belongs to the 74AC logic family, known for high-speed CMOS performance. It serves as a specialized digital comparator within the broader 74xx series ecosystem. The device complements other logic gates by providing dedicated arithmetic comparison functionality in a compact surface-mount package suitable for dense circuit designs.

Replacement Considerations

Check for equivalents such as the 74ACT521SC from onsemi, which shares similar functional characteristics. Verify pinout compatibility before substitution. Ensure voltage levels and package dimensions match the original design constraints.