The LT1004CZ-1.2#PBF is a two-terminal shunt reference that regulates a fixed 1.235 V output by shunting current through the cathode to ground — think of it as a precision Zener that holds its voltage to ±0.3% without an external resistor divider. The 20 mA output current ceiling means it can source a modest load directly, while the 10 µA minimum cathode current is the floor below which the reference drops out of regulation, so the series resistor from the supply must be sized to keep at least 10 µA flowing even at no load.
TO-92-3 package — board-fit and thermal reality
The TO-92-3 (TO-226AA) through-hole package is the same three-lead transistor outline used for decades — the pinout is standard (cathode, anode, no-connect), so it drops into existing footprints without a layout change. Temperature drift is specified at 20 ppm/°C typical — over the full 70°C span that adds about 1.7 mV of shift on the 1.235 V output, which is tight enough for a 0.1% system but not for a sub-0.05% metrology reference.