The MMSZ5226BT1G is a 3.3V 500mW Zener diode from onsemi in SOD-123 package, with 2% tolerance (B suffix). The Zener diode operates in reverse breakdown: when reverse-biased above 3.3V, the diode conducts and maintains approximately 3.3V across its terminals. The Zener impedance is 28 ohms at IZT = 20mA, meaning a 1mA current change produces 28mV voltage change. The temperature coefficient is approximately -1.5mV/C for 3.3V Zener (negative, as Zeners below 5.6V have negative tempco). The 500mW power rating limits maximum Zener current to approximately 150mA at 3.3V. A series resistor must be used: RS = (VIN – VZ) / (IZ + ILOAD). The SOD-123 package provides 300C/W thermal resistance. The -BT1G suffix specifies 2% tolerance, SOD-123, lead-free, tape-and-reel. Applications include: 3.3V logic level clamping, ESD protection, and voltage reference in low-precision circuits.