This part is a kind of semiconductor called AMS285-25AS.

Function of this product has MICROPOWER VOLTAGE REFERENCE DIODE.

Manufacturers : Advanced Monolithic Systems

Image and pinout :

Some of the text within the PDF file :

Advanced Monolithic Systems FEATURES • ±20 mV (±0.8%) max. initial tolerance (A grade) • Operating Current 20µ A to 20mA • Low Voltage Reference 2.5V • Max. 0.6Ω Dynamic Impedance (A grade) • Low Temperature Coefficient • 1.2V Device and Adjustable Device also available AMS285-1.2 and AMS285 series, respectively AMS385-1.2 and AMS385 series. AMS285-2.5/AMS385-2.5 MICROPOWER VOLTAGE REFERENCE DIODE APPLICATIONS • Battery Powered Systems • Instrumentation • A/D, D/A Converters • Temperature measurement • Current sources • Notebook/Personal Computer • Monitors/ VCR/ TV • Pagers GENERAL DESCRIPTION The AMS285-2.5/AMS385-2.5 are two-terminal micropower band-gap voltage reference diodes. They feature a very low dynamic impedance and good temperature coefficien [ ... ]

AMS285-25AS PDF Datasheet Download