Fixed 1.225 V shunt reference in SOT-323-5
The STMicroelectronics LM4041BICT-1.2 is a precision shunt voltage reference delivering a fixed 1.225 V output with ±0.2% initial tolerance. It operates as a two-terminal shunt (Zener-like) device, requiring only an external series resistor to set the bias current from the supply rail. It is suited for precision analog bias, ADC/DAC reference, and low-drift voltage clamping in power supplies and sensor interfaces.
Tolerance and drift — the precision floor
The ±0.2% initial tolerance (B-grade) places this part between the tighter A-grade (±0.1%) and the looser C-grade (±0.5%) in the LM4041 family. For a 1.225 V output, ±0.2% translates to a maximum initial error of ±2.45 mV — tight enough for most 12-bit ADC references without external trimming. The 60 µVrms noise (10 Hz to 10 kHz) is low enough for precision analog front-ends, though a bypass capacitor at the reference output further reduces wideband noise.
Shunt topology — resistor selection matters
As a shunt reference, the LM4041BICT-1.2 conducts current from cathode to anode, and the external series resistor must be chosen to maintain the cathode current between the 50 µA minimum and 12 mA maximum. The resistor value is calculated as (V_supply - 1.225 V) / I_bias, where I_bias must exceed the load current plus the 50 µA minimum cathode current. The 12 mA maximum output current limits the load this reference can drive directly. For higher load currents, a buffer amplifier is needed; for lower loads, the 50 µA minimum cathode current ensures the shunt stays in regulation.