Adjustable shunt reference for precision bias and regulation
Rated for 100 mA continuous output current, the TL431QD can drive optocoupler LEDs, shunt regulators, and moderate loads directly. The 1 mA minimum cathode current sets the bias floor: the device needs at least 1 mA through the cathode to maintain regulation, so the series resistor from the supply must be sized to deliver that even at the minimum input voltage. This is a common oversight when adapting a 431 design from a higher-current variant — the bias resistor calculation changes.
Package and mounting — 8-SOIC in Tube
The 8-SOIC package (0.154" body width, 3.90 mm) is a standard JEDEC outline for small-signal ICs. The Tube shipping format is typical for engineering samples and low-volume reflow; for higher-volume tape-and-reel requirements, check the TL431QDR variant. The surface-mount footprint is compatible with standard SOIC-8 land patterns.
This part is a current-design-in choice for new builds, not a phase-out risk.