Precision shunt reference for feedback and bias rails
The Texas Instruments TL431BQDBZRG4 is a three-terminal adjustable shunt voltage reference that sets a 2.495 V minimum output with a ±0.5% tolerance, the B-grade selection for tighter regulation than the standard ±1% or ±2% variants. Rated for 100 mA continuous output current and a 700 µA minimum cathode current, it drives optocoupler LEDs in isolated power supplies and sets the feedback threshold in linear and switching regulators. The SOT-23-3 package (TO-236-3 / SC-59 footprint) keeps the board area small for dense power-converter layouts.
Tolerance and temperature grade — what the B-grade buys
The ±0.5% initial tolerance on the 2.495 V reference reduces the feedback divider error budget, which matters when the output voltage of a 3.3 V rail must stay within ±2 % over line and load. Output voltage is adjustable up to 36 V by selecting the external resistor divider — the same pinout as the industry-standard TL431, so it drops into existing layouts without a board spin.