7.2 Long-Term Stability

Long-term stability is a key performance parameter for series voltage references in all precision applications.

This is defined as variation of reference voltage over time. The long-term stability value is tested in a typical

setup that reflects standard PCB board manufacturing practices. The boards are made of standard FR4 material,

the board does not have special cuts or grooves around the devices or go through burn-in process to relieve the

mechanical stress of the PCB. These conditions reflect real world use case scenario and common manufacturing

techniques.

During the long-term stability testing, precautions are taken to make sure that only the long-term stability drift is

being measured. The boards are maintained at 35°C ± 0.02°C in an oil bath. The oil bath makes sure that the

temperature is constant across the device over time. The measurements are captured every 30 minutes with a

calibrated 8.5 digit multimeter.

Typical long-term stability characteristic are expressed as a deviation over time. Figure 7-2 shows the typical drift

value for the REF54 VOUT is 25 ppm from 0 to 1000 hours. Long term stability depends on the board orientation

and thickness. The REF54 experiences the highest drift in the initial 1000 hr, subsequent deviation is typically

lower than previous 1000 hours.

Figure 7-2. Long Term Stability SOIC -1000 hours (VOUT)

7.3 Noise Performance

7.3.1 1/f Noise

1/f noise, also known as flicker noise, is dominant mostly in the lower frequency bands. REF54 data sheet

specifies flicker noise for 0.1 Hz to 10 Hz frequency band where 1/f noise has maximum power. 1/f noise is

specified as real time error in terms of peak to peak variation of reference voltage over 10 second time window

(to capture minimum 0.1 Hz noise) on oscilloscope (with sampling frequency much more than 20 Hz). Since the

1/f noise is an extremely low value, the frequency of interest is amplified and filtered through a precise band filter

with very low noise floor as shown in Figure 7-3.

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REF54

SNVSCN7 – NOVEMBER 2023

Copyright © 2023 Texas Instruments Incorporated

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