Description
The TL431Z is a three-terminal adjustable regulator series with a guaranteed thermal stability over applicable temperature ranges. The output voltage may be set to any value between Vref (approximately 2.5 volts) and 40 volts  with two external resistors. These devices have a typical dynamic  output impedance of 0.2Ω.  Active output circuitry

FEATUREs
•Programmable Output Voltage to 40V
•Low Dynamic Output Impedance 0.2Ω
•Sink Current Capability of 0.1 mA to 100 mA
•Equivalent Full-Range Temperature Coefficient of 50 ppm/^oC
•Temperature Compensated for Operation over Full Rated Operating Temperature Range
•Low Output Noise Voltage
•Fast Turn on Response
•TO-92, SOP- 8, SOT-23, SOT-89 packages