±1% tolerance — the precision tier in the TL431 family
The TL431ACDG4 is Texas Instruments' adjustable shunt voltage reference with a ±1% initial tolerance on the 2.495 V internal reference. That tolerance grade is the key spec: it moves this part above the standard TL431 (±2%) and into the precision tier, where the output voltage accuracy after the divider network stays inside ±1% without trimming.
100 mA shunt capacity and the bias resistor decision
The cathode can sink up to 100 mA continuously. For a typical 5 V rail with a 2.5 V reference, the minimum bias resistor is (5 V – 2.495 V) / 0.1 A ≈ 25 Ω — but that's the thermal floor; in practice a 1 kΩ resistor keeps the cathode current near 2.5 mA, well above the 600 µA minimum to maintain regulation, and leaves headroom for load transients.
8-SOIC package — layout and thermal note
Housed in the industry-standard 8-SOIC (0.154" width, 3.90 mm body), this part shares the footprint with countless other SOIC-8 shunt references and op-amps. The 100 mA cathode current at 36 V max output means up to 3.6 W dissipation if the device is asked to regulate near the voltage ceiling at full current — the copper pour on the cathode tab side of the PCB needs to handle that thermal load. For most designs running at a few milliamps, the standard SOIC-8 layout is fine.