8.2 Long-Term Stability

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.

Time (hr)

0

800

1600

2400

3200

4000

-200

-150

-100

-50

0

50

100

150

200

Figure 8-3. Long Term Stability LCCC -4000 hours (VOUT)

8.3 Thermal Hysteresis

Thermal hysteresis is measured with the REF70 FKH soldered to a PCB, similar to a real-world application.

Thermal hysteresis for the device is defined as the change in output voltage after operating the device at 25°C,

cycling the device through the specified temperature range, and returning to 25°C. This can be seen in Figure

8-4 to Figure 8-5. Hysteresis can be expressed by Equation 1:

6

PRE

POST

HYST

NOM

| V

V

|

V

10

ppm

V

§

·

u

¨

¸

©

¹

(1)

where

• VHYST = thermal hysteresis (in units of ppm)

• VNOM = the specified output voltage

• VPRE = output voltage measured at 25°C pre-temperature cycling

• VPOST = output voltage measured after the device has cycled from 25°C through the specified temperature

range of –40°C to +125°C and returns to 25°C.

REF70

SNAS781E – OCTOBER 2020 – REVISED JULY 2022

www.ti.com

18

Submit Document Feedback

Copyright © 2022 Texas Instruments Incorporated

Product Folder Links: REF70