Precision shunt reference — what the ±0.2% tolerance means for your BOM
The LT1009ILP is a 2.5V shunt reference from Texas Instruments, trimmed to ±0.2% initial tolerance and 35ppm/°C temperature drift. Shunt topology means it behaves like a two-terminal Zener — it regulates by shunting current through the cathode to ground. The 400 µA minimum cathode current sets the floor for the bias resistor; below that the reference drops out of regulation. At the other end, the 10 mA output ceiling limits the load the reference can drive directly — for higher-current loads, buffer it with an op-amp.
TO-92-3 package — board-fit and assembly reality
The LT1009ILP ships in a TO-92-3 (TO-226AA) through-hole package. The three leads are on 0.050-inch pitch, 0.200-inch row spacing — standard for the TO-92 footprint that has been in production for decades. Through-hole assembly means it survives wave-solder and hand-solder rework without the thermal stress concerns of a small-outline SMD package. The package body is bulk-packed, not tape-and-reel, so it is typically kitted by hand or fed through a tube feeder for automated insertion.
Active lifecycle and compliance — no obsolescence risk today
It is ROHS3 compliant, meaning no restricted-substance exemptions that would trigger a PCN for material change. For a BOM that already qualifies this reference, there is no immediate pressure to qualify a replacement.