Reference voltage for the analog chain
The LM4040D20ILPRE3: The ±1% initial tolerance sets the absolute accuracy floor of the conversion; in a 12-bit system with a 4.096 V reference, 1% error consumes about 40 LSBs of the dynamic range before any temperature or aging effects are added.
Temperature drift and noise budget
In a 1 kHz signal bandwidth, the integrated noise contribution from the reference is roughly 11 µVrms — well below the quantization noise floor of a 12-bit ADC sampling a 2 V input range.
Shunt topology — external resistor required
As a shunt reference, the LM4040D20ILPRE3 requires an external series resistor between the supply rail and the reference cathode to set the bias current. The cathode current range of 80 µA (minimum) to 15 mA (maximum) defines the allowable resistor value window: for a 5 V supply, a 1.5 kΩ resistor biases the reference at roughly 2 mA, keeping it well above the minimum while leaving headroom for the 15 mA output current capability.
Through-hole package — legacy board integration
The TO-92-3 (TO-226AA) package with formed leads is a through-hole footprint with 2.54 mm pitch. It mates with standard 0.100-inch header sockets or can be soldered directly into plated through-holes. The package suits prototyping, low-density designs, and applications where vibration resistance is not critical — the cantilevered leads offer less mechanical retention than a surface-mount package with glue dots.
The part is ROHS3 compliant, meeting current EU substance restrictions without exemption.