TLV431x Low-Voltage Adjustable Precision Shunt Regulator.
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 any value between VREF (1.24 V) and 6 V with two external resistors (see the Parameter Measurement Information section). These devices operate from a lower voltage (1.24 V) than the widely used TL431 and TL1431 shunt-regulator references.
When used with an optocoupler, the TLV431 device is an ideal voltage reference in isolated feedback circuits for 3-V to 3.3-V switching-mode power supplies. These devices have a typical output impedance of 0.25 Ω. Active output circuitry provides a very sharp turnon characteristic, making them excellent replacements for low-voltage Zener diodes in many applications, including on-board regulation and adjustable power supplies. YAC6, YACU SMD IC Data sheet pdf
