±1% initial tolerance — the accuracy anchor for the rail
The TL431AQDCKR is a precision adjustable shunt reference from the TL431 family, specified with a ±1% initial tolerance. That tolerance is the ceiling on the reference voltage error at 25 °C before temperature drift and aging add their contributions — for a 3.3 V rail derived from a 2.495 V reference, ±1% means the set point is within 25 mV of target at room temperature, which keeps the downstream regulator or ADC reference within its input common-mode window.
2.495 V to 36 V — one reference covers multiple rail voltages
That range covers the common 3.3 V, 5 V, 12 V, and 24 V bus references from a single BOM line — no need to qualify a different fixed-voltage reference for each rail. The 100 mA cathode current rating means it can sink enough current to drive the optocoupler LED in a feedback loop for a medium-power offline supply without an external buffer transistor.
The 700 µA minimum cathode current is the quiescent floor — below that the shunt drops out of regulation, so the bias resistor must be sized to keep at least 700 µA flowing at the lowest input voltage and highest load current.
SC-70-6 footprint — board-area trade-off
The part is offered in a 6-pin SC-70-6 (SOT-363) package. The 0.65 mm pin pitch and 2.0 mm × 1.25 mm body save about 60% board area versus an SOIC-8.