2.49V shunt reference — the BOM-fit angle
The ±4% tolerance means the actual output can sit anywhere from about 2.39V to 2.59V; that's a cost-optimised bin, not a precision grade. If your ADC needs better than 40 mV accuracy, you'll want a tighter-tolerance sibling or a trim network. The TO-92-3 through-hole package is the classic three-lead transistor outline — easy to hand-assemble, breadboard, or retrofit into existing PTH boards.
Cathode current and output compliance
As a shunt reference, the LM336LPE3-2-5 sinks current through the cathode to ground. The cathode current floor is 400 µA — below that the reference may not regulate. Maximum output current is 10 mA, which covers biasing a handful of op-amp inputs or a low-power ADC reference input.
