±0.5% tolerance — the precision tier of the low-voltage shunt family
The Texas Instruments TLV431BQDBZR is a low-voltage adjustable shunt voltage reference that regulates from 1.24V up to 6V, with a guaranteed ±0.5% tolerance across temperature. That tolerance is the headline differentiator: it sits one grade above the standard TL431's ±1% and two above the ±2% 'A' suffix parts, making it the choice when the reference accuracy directly sets the ADC threshold or regulator feedback divider error budget. The 100 µA minimum cathode current is the floor for bias — below that the shunt drops out of regulation, so the biasing resistor needs to deliver at least that at minimum input voltage and maximum load. Output current is rated 15 mA, enough to drive the optocoupler LED in a flyback supply or bias a handful of comparator inputs.
SOT-23-3 — footprint and thermal reality
The TLV431BQDBZR comes in the SOT-23-3 package (also listed as TO-236-3 / SC-59). It is a three-pin shunt, so the layout is straightforward: cathode, anode, and the reference/feedback pin. The SOT-23-3 dissipates through the leads and the small epoxy body — at 15 mA output with a 5V drop (75 mW), the junction rise is modest, but if you push the full 15 mA at 6V dropout (90 mW) in a 125°C ambient, the junction temperature approaches the absolute maximum. Surface-mount assembly is standard MSL 1 per the ROHS3 compliance — no bake required before reflow if the bag seal is intact.
The ROHS3 compliance is current, so no exemption expiry to track.
The 1.24V minimum output makes it suitable for sub-3.3V rails where a standard TL431's 2.5V reference would eat too much headroom. The shunt topology also means it sinks current rather than sourcing it, so it is not a direct fit for a series-regulator reference input without a pull-up resistor.