Fixed 2.5V shunt reference in SC-70-5
The Texas Instruments LM4040C25IDCKR is a precision shunt voltage reference delivering a fixed 2.5V output with ±0.5% initial tolerance. It is part of the LM4040 series, a widely used family of low-power, high-accuracy references for ADC biasing, comparator thresholds, and power supply supervision. The SC-70-5 package (also known as SOT-353) measures roughly 2.0 mm × 2.1 mm, making it a fit for dense PCB layouts where board area is at a premium. The shunt topology means it behaves like a two-terminal Zener — it requires a series resistor from the supply and sinks current to regulate the output voltage.
Tolerance, noise, and temperature drift
The ±0.5% tolerance covers initial accuracy at 25°C — enough margin for 8-bit ADC references and most comparator-based threshold circuits. This is low enough for most data converter references in industrial control and instrumentation, though a low-pass filter at the reference output helps in noise-sensitive signal chains.
Cathode current and output drive
The LM4040C25IDCKR sinks a minimum cathode current of 80 µA and can deliver up to 15 mA to the load. The 80 µA floor sets the minimum bias current through the series resistor — design the resistor value so that at minimum supply voltage the reference sees at least 80 µA plus the load current. The 15 mA ceiling limits how many ADC inputs or comparator nodes it can drive directly; beyond that, buffer with an op-amp.
No direct pin-compatible replacement is needed at this time.