The TLV431 device is a low-voltage 3-terminal adjustable voltage reference with specified thermal stability over applicable industrial and commercial temperature ranges. Output voltage can be set to 1.24V on stand alone mode or any value between VREF (1.24V) and 6V with two external resistors (see Figure 6-2). These devices operate from a lower voltage (1.24V) than the widely used TL431 and TL1431 shunt-regulator references. When used with an optocoupler, the TLV431 device is a voltage reference in isolated feedback circuits designed for 3V to 3.3V switching-mode power supplies. These devices have a typical output impedance of 0.25Ω. Active output circuitry provides a very sharp turn-on characteristic, making them excellent replacements for low-voltage Zener diodes in many applications, including on-board regulation and adjustable power supplies.