1.225 V shunt reference — the accuracy floor for your ADC or comparator
The STMicroelectronics LM4041AICT-1.2 is a precision shunt voltage reference with a fixed 1.225 V output. It uses a shunt (two-terminal) topology, so it behaves like a Zener diode — you bias it with a resistor from the supply, and the reference regulates the voltage across itself by sinking current through the cathode. The initial tolerance is ±0.1%, which means the output voltage at 25 °C is guaranteed within 1.225 V ± 1.225 mV. That is tight enough for a 12-bit ADC reference without external trimming, provided the temperature drift is accounted for in the system budget. Temperature coefficient is 100 ppm/°C.
Shunt topology — bias resistor and cathode current matter
The shunt reference requires an external series resistor from the supply to the cathode. The resistor must supply the load current plus the minimum cathode current of 50 µA, while staying below the 12 mA maximum output current. The 60 µVrms noise spec (10 Hz to 10 kHz) is low enough for most precision analogue circuits. If your design needs lower noise, a 0.1 µF bypass capacitor from cathode to anode reduces the wideband noise further — the shunt topology responds well to a local decoupling cap.
Package and footprint — SOT-353 with SOT-323-5 supplier device
The LM4041AICT-1.2 is offered in a 5-lead SOT-353 package, also described as SC-70-5. The small size suits space-constrained designs but demands careful solder-paste stencil design to avoid bridging on the fine-pitch leads. Mounting is surface mount only.
Lifecycle and sourcing
The base product number LM4041 covers a family of fixed and adjustable shunt references — if you need a different voltage or tolerance, the LM4041 series offers several options in the same SOT-353 footprint.