1.24 V adjustable shunt — tolerance and bias floor
The TLV431IDBVRG4 is a low-voltage adjustable shunt reference from Texas Instruments, built on the same topology as the industry-standard TL431 but trimmed for a 1.24 V minimum output instead of 2.5 V. The reference voltage tolerance is ±1.5% — tight enough for a 5% output regulation budget in an isolated DC-DC secondary-side feedback loop or a battery-monitor threshold. Output is adjustable from 1.24 V up to 6 V via two external resistors, making it a direct fit wherever a sub-2.5 V precision rail is needed — think 1.8 V or 2.5 V secondary references on a mixed-signal board.
Output current and cathode bias — sizing the resistor
The shunt can sink up to 15 mA of cathode current — that sets the upper limit on the load you can regulate and the current through the bias resistor from the supply rail. The minimum cathode current to maintain regulation is 80 µA, so the bias resistor must be sized to deliver at least that much at the lowest supply voltage and highest output voltage setting.
Package and temperature — board-fit realities
Housed in a SOT-23-5 (SC-74A) surface-mount package, the same footprint as the standard TLV431 in SOT-23-5.