This part is a kind of semiconductor called AP431.

Function of this product has Adjustable Precision Shunt Regulator.

Manufacturers : Anachip

Image and pinout :

Some of the text within the PDF file :

Adjustable Precision Shunt Regulator AP431/AP431A „ Features „ Description • Precision reference voltage AP431 : 2.495V ± 1% AP431A : 2.495V ± 0.5% • Sink current capability: 200mA • Minimum cathode current for regulation: 300μA • Equivalent full-range temp coefficient: 30 ppm/oC • Fast turn-on response • Low dynamic output impedance: 0.2Ω • Programmable output voltage to 36v • Low output noise. • Packages: TO92, SOT89, SOT23, SOT25 and SOP The AP431/AP431A are 3-terminal adjustable precision shunt regulators with guaranteed temperature stability over the applicable extended commercial temperature range. The output voltage may be set at any level greater than 2.495V(VREF) up to 36V merely by selecting two external resistors that act as a voltage divider networ [ ... ]

AP431 PDF Datasheet Download