APT1211S is a phototriac coupler in SOP4 package designed for AC triac ignition and control in industrial machinery and consumer electronics. It features a zero-cross detection method with a maximum zero-cross voltage of 50 V, enabling precise switching at AC line zero-crossings to minimize EMI and switching noise. The device is rated for 600 V repetitive peak OFF-state voltage and 50 mA ON-state RMS current, with an operating temperature range of -40°C to +100°C. Key electrical characteristics include a maximum LED dropout voltage of 1.3 V, holding current of 3.5 mA maximum, and I/O isolation voltage of 3,750 Vrms. The APT1211S is certified to safety standards including C-UL (UL1577) and VDE (EN60747-5-5), making it suitable for triac drivers in SSRs, heater controls, and 100 V/200 V 50/60 Hz AC line applications.