There are multiple methods of applying a reference voltage to the device. A straightforward approach is to apply a voltage to the VREF test point with U2 unpopulated. If a buffered voltage is desired, then U2 can be populated with an operational amplifier in an appropriate DBV package with the OUT pin on pin 1. Ensure the series resistor R15, as well as any accompanying passive components, are populated before using the reference buffer.

If the reference voltage is GND, then either R17 can be populated with a 0-Ohm resistor or the VREF test point can be connected to GND. When grounding the reference pin, ensure R15 is not populated.