Precision shunt reference in a SOT-23-3
The Texas Instruments LM4051AIM3X-1.2/NOPB is a precision shunt voltage reference delivering a fixed 1.225 V output with ±0.1% initial tolerance.
The ±0.1% tolerance at 25°C sets the initial accuracy floor for an ADC reference or comparator threshold — a 1.225 V nominal output stays within 1.223 V to 1.227 V at room temperature. For a 12-bit ADC with a 2.5 V span, that drift is under 1 LSB; for 16-bit systems it starts to eat into the noise budget and may require a calibration step.
Shunt topology — cathode current and output drive
As a shunt reference, the LM4051 sinks current through the cathode to maintain regulation. The minimum cathode current is 65 µA — below that the reference drops out of regulation. Maximum continuous output current is 12 mA, which covers biasing a single ADC reference input or a comparator string, but not multiple heavy loads. The 20 µVrms noise (10 Hz to 10 kHz) is low enough for most 12- to 14-bit SAR ADC applications without additional filtering.
SOT-23-3 package and surface-mount assembly
Housed in a three-lead SOT-23-3 (TO-236-3, SC-59 equivalent), this part is a drop-in for standard shunt reference footprints. The surface-mount package suits automated pick-and-place and reflow assembly. No exposed pad — thermal performance depends on the copper area on the cathode pin trace, so keep the trace short and wide if the part is sinking near the 12 mA maximum.