PhotoMOS SPST-NO signal relay, 120 mA continuous
The AQY221N2MY is a PhotoMOS™ AQY series solid-state relay from Panasonic Electric Works, configured as a single-pole single-throw normally-open (SPST-NO, 1 Form A) output. It switches AC or DC (RF) loads up to 120 mA continuous across a 0 V to 40 V rail, with a maximum on-state resistance of 12.5 Ohms. Housed in a 4-SON (small-outline no-lead) package measuring 2.95 mm on the longest side, the part suits compact, low-profile PCB layouts where a mechanical relay would consume too much board area or height.
On-resistance and load current: what limits the signal path
The 12.5 Ohm max on-resistance (Ron) is the dominant term in the insertion loss for this relay. Because the output is a bidirectional MOSFET pair (AC/DC switch), Ron is symmetrical and the part blocks voltage in both polarities when off. The 40 V load voltage rating is the peak blocking voltage, not a continuous bias — the relay handles line-level audio, small-signal analog multiplexing, and low-power DC switching within that envelope. No minimum load current or wetting current requirement exists for a solid-state relay — the AQY221N2MY switches dry contacts without the oxide-piercing current a mechanical relay needs, which is the reason it is specified for RF and low-level analog paths.
The 4-SON package has a 2.95 mm body width and a 0.50 mm pitch between the SMD tabs. The land pattern is the same as a standard SOT-23-5 footprint, so the relay can be placed on a common pad layout without a custom stencil. Termination style is SMD (SMT) Tab — the two output pads are larger than the input pads, which helps with thermal dissipation from the output FETs when switching near the 120 mA limit. Supplied in Tape & Reel (TR) or Cut Tape (CT) packaging; the reel quantity is not listed, but the base part number AQY221 covers the full family, so the suffix MY identifies the specific tape-and-reel variant.