Precision shunt reference in a small SOT-23-3
The onsemi TL431BCDBZT is an adjustable shunt voltage reference — the classic three-terminal programmable regulator that shows up in feedback loops, power-supply error amps, and precision reference circuits. The B-grade brings tighter initial accuracy: ±0.5% tolerance on the 2.495 V internal reference, which matters when you're setting the output voltage of a flyback converter or the threshold of an overvoltage crowbar.
Output current and cathode current — the drive budget
Rated for 100 mA output current, the TL431BCDBZT can sink enough current to pull down an optocoupler LED in a secondary-side feedback loop or drive a small load directly. Minimum cathode current is 600 µA — below that the reference loses regulation, so the bias resistor must be sized to keep at least 600 µA flowing through the device at all times.
Housed in a SOT-23-3 (TO-236-3 / SC-59) surface-mount package, the TL431BCDBZT fits tight layouts where board space is at a premium.
Active production, no LTB worry
That means no last-time-buy scramble for existing BOMs, and it stays available for new designs that don't need the extended industrial temperature range.