The TS431 is a three-port, low-voltage, adjustable shunt voltage reference. The output voltage can be adjusted via two external resistors to any value between Vref (1.24 V) and 6 V. The TS431 can operate at a lower voltage (1.24 V) and a lower cathode current than the widely used TL431 and TL1431 shunt voltage references. When controlling an optocoupler, the TS431 is particularly suitable for the control of 3.3 V switching power supplies.