It provides a stable 2.495 V reference between the cathode and anode, and with an external resistor divider the output can be set anywhere from that minimum up to 36 V. The 100 mA cathode-current rating means it can serve as both a precision reference and an error amplifier in linear and switched-mode power supplies, or as a series-pass element in low-dropout regulator loops. The ±2.21% tolerance is the commercial-grade bin — adequate for general-purpose regulation where a tighter band (like the 0.5% or 1% grades) isn't required.
Output voltage range — what the 2.495 V reference and 36 V ceiling mean for your rail
The TL431CCT's internal bandgap reference sits at 2.495 V (the minimum output when the adjust pin is tied to the cathode). With two external resistors you can program the output anywhere from that floor up to 36 V. That 36 V ceiling covers most 12 V, 24 V, and even 28 V auxiliary rails in industrial and telecom supplies. The cathode current must stay above 1 mA to maintain regulation, so the resistor divider needs to be sized to draw at least that much.
Package and footprint — SOT-323-6L versus the classic SOT-23
The TL431CCT is supplied in a 6-lead SOT-323-6L (also listed as SOT-363). That's a smaller body than the familiar SOT-23-3 used by many TL431 variants — roughly 2.1 mm × 2.0 mm versus 2.9 mm × 1.6 mm. The pinout differs, so a drop-in replacement for a SOT-23 TL431 footprint isn't possible without a layout change. Store the reels dry — the MSL rating isn't listed, but SOT-323 packages typically carry MSL 1 or 2; if the bag's humidity indicator shows pink, bake before reflow.
That means no last-time-buy scramble and no forced redesign for the foreseeable future. The part is ROHS3 compliant.