2.495 V reference, adjustable to 36 V — the ±0.5% grade
The TL431BCPKG3 is a three-terminal adjustable shunt regulator that sets a 2.495 V reference between the cathode and the reference pin, with the output programmable up to 36 V via two external resistors. The ±0.5% tolerance (B grade) is the tightest standard option in the TL431 family — a meaningful step up from the ±2.2% of the TL431IDBVR variant when the reference voltage needs to stay inside a narrow window over temperature and load. Sinking up to 100 mA at the cathode with a minimum 600 µA bias current, this part fits as the error amplifier in an isolated flyback supply, the shunt in a precision clamp, or the programmable reference in a linear regulator feedback loop. The commercial temperature range (0°C to 70°C) limits it to indoor or controlled-environment gear — not a candidate for an automotive or outdoor sensor node.
SOT-89-3 footprint and board-fit
Housed in the TO-243AA (SOT-89-3) surface-mount package, the TL431BCPKG3 shares the same three-pin layout as the standard TL431 in SOT-89 — cathode, anode, reference. The wide tab on the backside is the anode and carries the thermal path; a copper pour under the tab on the PCB drops the junction-to-ambient thermal resistance. No exposed pad beyond the tab, so no special via pattern is needed.
Active lifecycle, ROHS3, and sourcing posture
For new designs the part is a safe choice; the TL431 core has been in production for decades and is second-sourced across multiple vendors, so single-source risk is low. The ±0.5% B-grade is less common than the ±1% or ±2% variants, so confirm the tolerance requirement before substituting a looser grade.