The REF35-Q1 will experience the highest drift in the initial 1000 hr. Subsequent deviation is typically lower than

first 1000 hr.

Time (hr)

0

200

400

600

800

1000

-200

-100

0

100

200

Figure 8-4. Long Term Stability - 1000 hours (VREF)

8.4 Thermal Hysteresis

Thermal hysteresis is measured with the REF35-Q1 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. The PCB was baked

at 150°C for 30 minutes before thermal hysteresis was measured. Use Equation 2 to calculate the thermal

hysteresis.

6

PRE

POST

HYST

NOM

| V

V

|

V

10

ppm

V

§

·

u

¨

¸

©

¹

(2)

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.

Figure 8-5 and Figure 8-6 show the typical thermal hysteresis distribution across various temperature ranges in

two cycles.

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REF35-Q1

SNAS845 – AUGUST 2023

Copyright © 2023 Texas Instruments Incorporated

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Product Folder Links: REF35-Q1