Adjustable shunt reference — the ±1% grade that tightens the setpoint
The TL431AQDCKT is the ±1% tolerance variant of the industry-standard TL431 adjustable shunt reference from Texas Instruments. It sinks up to 100 mA through the cathode while regulating the reference pin to 2.495 V, with the output adjustable up to 36 V via two external resistors. The Q-grade suffix selects the tighter tolerance bin — important when the regulator output must stay within a few millivolts of target across temperature.
Output range and cathode current — sizing the bias resistor
The minimum regulated voltage is 2.495 V (the internal reference), and the maximum is 36 V — set by the resistor divider from cathode to reference to anode. The cathode current floor is 700 µA (typical), which sets the minimum bias current through the pull-up resistor to keep the device in regulation. At 100 mA maximum continuous cathode current, the part can drive an optocoupler LED directly in a secondary-side feedback loop without an extra buffer transistor.
SC-70-6 package — footprint for dense boards
Housed in a 6-lead SC-70-6 (SOT-363 compatible), the TL431AQDCKT occupies roughly half the PCB area of the SOIC-8 version. The mounting type is surface-mount, with tape-and-reel or cut-tape options for the BOM line. The small body means the power dissipation is package-limited — at 100 mA cathode current and a cathode-to-anode voltage drop of, say, 12 V, the 1.2 W dissipation exceeds the SC-70-6's capability without a copper pour; derate for the actual Vka and ambient temperature.
For dual-sourcing or second-source qualification, the base TL431 family has multiple suppliers (ON Semiconductor, STMicroelectronics, NXP) with pin-compatible devices, though the ±1% Q-grade tolerance may not be available from every alternate vendor — confirm the tolerance bin on the cross before swapping.