onsemi has marked the CNY173S as obsolete, meaning the original manufacturer no longer produces this part. New-old-stock and surplus inventory are sourced through independent distribution channels. For a BOM line that requires this exact 5300Vrms isolation and 100-200% CTR window, the existing inventory is the only path.
5300Vrms isolation and CTR window
The 5300Vrms isolation rating qualifies this optoisolator for reinforced insulation in mains-connected circuits — think AC line monitoring, motor drive feedback, or medical equipment where the safety barrier must hold off transient overvoltages. Current transfer ratio (CTR) is specified at 100% minimum to 200% maximum at If=10mA. This 2:1 window means the output transistor saturates reliably across the full input current range, but the designer must budget the minimum CTR for worst-case LED degradation over temperature and life. Output side handles up to 70V and 50mA continuous — suitable for driving logic inputs, PLC digital inputs, or low-power relays. The 300mV Vce saturation at rated current keeps the voltage drop low enough to avoid pulling the output rail down.
Switching speed and temperature range
Rise/fall times of 1µs and 2µs typical, with turn-on/turn-off at 2µs and 3µs typical, limit this part to low-speed isolation — think 10kHz or below. It works for DC state sensing, switch debouncing, or 50/60Hz zero-cross detection, but not for high-speed serial isolation. The -55°C to 100°C operating range covers industrial enclosures and some military/aerospace environments. The 6-SMD gull wing package mounts on standard surface-mount pads with a 1.6mm PCB thickness profile — no special reflow profile beyond the standard lead-free solder curve.