8 Parameter Measurement Information

8.1 Long-Term Stability

Buried zener references typically exhibit very stable long term stability and used as a ultra stable reference

for internal calibration of the signal chain system. The long-term stability value is tested in a typical setup that

reflects standard PCB board manufacturing practices for references with strain modulation structure around the

device. The boards are made of standard FR4 material with 35µm of Copper.

Long term stability setup is designed with utmost care to minimize impact of thermocouple error, strain impact

and mechanical vibration in long term stability measurement. The boards are maintained at 25°C in an air drift

oven with heater temperature set to 115°C in powered on condition for long term stability measurement.

Typical long-term stability characteristic is expressed as a deviation over time. Figure 8-1 shows the typical drift

value for the REF80 VREF_Z is 9ppm from 0 to 300 hours. Drift of REF80 quickly settles around 300 hours.

Subsequent deviation is typically lower than 1ppm for the next 1000hr.

Time (Hours)

0

200

400

600

800

1000

-20

-10

0

10

20

Avg

Avg + Std dev

Avg - Std dev

Figure 8-1. Long Term Stability (VREF_Z)

8.2 Temperature Drift

The REF80 has integrated on chip heater, which is factory programmed to TSET = 105°C temperature. Heater

regulates the TSET temperature to ± 1°C for entire operating temperature range. This results in 0.05ppm/°C

tempco for REF80.

The temperature coefficient is calculated using the box method in which a box is formed by the min/max

variation for the nominal output voltage over the operating temperature range. REF80 has a maximum

temperature coefficient of 0.2ppm/°C for 0°C to70°C temperature range. The box method specifies limits for

the temperature error but does not specify the exact shape and slope of the device under test. See SLYT183 for

more information on the box method. The box method equation is shown in Equation 2:

REF(MAX)

REF(MIN)

6

REF(25 C)

V

V

Drift

10

V

Temperature Range

q

§

·

u

¨

¸

¨

¸

u

©

¹

(2)

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REF80

SNAS856 – SEPTEMBER 2024

Copyright © 2024 Texas Instruments Incorporated

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