The TS4431 is a four-terminal device dedicated to low voltage Switch Mode Power Supplies (SMPS). It integrates a 1.224V voltage reference, an amplifier, and an open collector output transistor in a single package. The TS4431's operating mode is similar to the well-known standard voltage reference, the TL431. It maintains the desired feedback voltage at the REF pin in a closed loop configuration by sinking a current proportional to the error voltage at the REF pin. TS4431 features an open collector transistor with an ultra-low saturation voltage, allowing it to be used in series with the optocoupler in an SMPS architecture to regulate low voltage SMPS.