The AQY221N1SX is listed as obsolete by Panasonic Electric Works, meaning the manufacturer no longer produces this exact order code (cites:). For a BOM that already carries this relay, the 120 mA load current at 40 V and the 1.14 VDC input threshold are the fit-critical parameters — the SPST-NO circuit and 4-SOP footprint are the mechanical constraints (cites:,).
Parametric profile — 120 mA, 12.5 Ohm on-state
Rated for 120 mA continuous load current across 0 V to 40 V AC or DC — the RF output type means it handles RF signal switching without adding significant distortion (cites:,). On-state resistance is 12.5 Ohms maximum, which sets the voltage drop at full load to about 1.5 V — relevant for low-voltage signal paths where the relay's own drop must stay below the logic threshold (cites:,).
Sourcing an obsolete relay
No official successor order code is recorded in the lifecycle data — a pin-compatible replacement within the PhotoMOS AQY family would need to match the 4-SOP footprint, SPST-NO circuit, and 1.14 V input threshold (cites:,).