SNAS781E October 2020 – July 2022 REF70
One of the key parameters of the REF70 references is long-term stability also known as long-term drift. The long-term stability value was tested in a typical setup that reflects standard PCB board manufacturing practices. The boards are made of standard FR4 material and the board does not have special cuts or grooves around the devices to relieve the mechanical stress of the PCB. The devices and boards in this test do not undergo high temperature burn in post-soldering prior to testing. These conditions reflect a real world use case scenario and common manufacturing techniques.
During the long-term stability testing, precautions are taken to ensure that only the long-term stability drift is being measured. The boards are maintained at 35°C in an oil bath. The oil bath ensures that the temperature is constant across the device over time compared to an air oven. The measurements are captured every 30 minutes with a calibrated 8.5 digit multimeter.
Typical long-term stability characteristic is expressed as a deviation over time. Figure 8-3 shows the typical drift value for the REF70 FKH VOUT is 35 ppm from 0 to 1000 hours. It is important to understand that long-term stability is not ensured by design and that the value is typical. The REF70 will experience the highest drift in the initial 1000 hr. Subsequent deviation is typically lower than 13 ppm for the next 1000 hr.