8-bit identity comparator in 20-SOIC
The Renesas 74FCT521ATSOG is an 8-bit identity comparator from the 74FCT series. It compares two 8-bit words and asserts the output when they match. The output is active-low, so a low signal on the A=B pin indicates equality. This part is used in address decoding, data bus matching, and parity-check circuits where a fast, glitch-free match signal is needed. The 20-SOIC package (7.50 mm width) is a common footprint for board-level glue logic. Output drive capability is 15 mA sinking and 48 mA sourcing, enough to feed a standard TTL input or drive an LED indicator through a series resistor.
Supply and timing — what matters for the bus
Quiescent current is only 10 µA, so the part adds negligible draw to the 5V rail when idle. The active current will be higher when inputs toggle, but for a glue-logic comparator this is rarely a power-budget concern.
Lifecycle and compliance
The 74FCT521ATSOG is listed as Active in production. It is ROHS3 compliant, so it passes the material restrictions for EU and most global markets without an exemption claim.