8.2 Temperature Coefficient

The REF35 is designed and tested for a low output voltage temperature coefficient, which is defined as the

change in output voltage over temperature. The temperature coefficient is calculated using the box method in

which a box is formed by the min/max limits for the nominal output voltage over the operating temperature range.

REF35 has a low maximum temperature coefficient of 10 ppm/°C from –40°C to +125°C and TBD ppm/°C from

–40°C to +85°C. The box method specifies limits for the temperature error but does not specify the exact shape

and slope of the device under test. Due to temperature curvature correction to achieve low-temperature drift, the

temperature drift is expected to be non-linear. See SLYT183 for more information on the box method. The box

method equation is shown in Equation 1

REF(MAX)

REF(MIN)

6

REF(25 C)

V

V

Drift

10

V

Temperature Range

q

§

·

u

¨

¸

¨

¸

u

©

¹

(1)

Figure 8-3 shows a typical voltage versus temperature curves across 32 devices. Figure 8-4 shows the

distribution of temperature coefficients across 32 devices.

Figure 8-3. Output Voltage Vs Free-Air

Temperature

Figure 8-4. Temperature Coefficient Distribution

REF35

SNAS809 – DECEMBER 2021

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