Fixed 3V shunt reference for precision bias and ADC references
The Texas Instruments LM4040A30IDCKRE4 is a precision shunt voltage reference with a fixed 3V output, ±0.1% initial tolerance, and a temperature coefficient of 100 ppm/°C.
Output current and cathode current — sizing the bias resistor
As a shunt reference, the LM4040A30IDCKRE4 sinks current through an external bias resistor connected between the supply and the cathode. The device can sink up to 15 mA of output current while requiring a minimum cathode current of 82 µA to maintain regulation. The bias resistor value must be chosen so that the cathode current stays between 82 µA and 15 mA over the full load and supply range — a common oversight that leads to dropout or excessive dissipation in tight-margin designs.
SC-70-5 package — board-area fit and layout consideration
The small footprint suits dense mixed-signal boards, but the low thermal mass means the bias resistor should be placed close to the cathode pin to minimise parasitic inductance and keep the reference stable under transient loads. The supplier device package is SC-70-5.