Time (hr)

0

400

800

1200

1600

2000

-200

-160

-120

-80

-40

0

40

80

120

160

200

Figure 8-5. Long Term Stability - 2000 hours (VREF)

8.4 Thermal Hysteresis

Thermal hysteresis is measured with the REF35 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 +85°C or –40°C to +105°C and returns to 25°C.

The graphs below show the typical thermal hysteresis distribution across various temperature ranges in two

cycles.

REF35

SNAS809A – DECEMBER 2021 – REVISED AUGUST 2022

www.ti.com

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