Thermal hysteresis is measured with the REF34xx 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. Hysteresis can be expressed by Equation 1:

Equation 1.

where

• V_HYST = thermal hysteresis (in units of ppm)
• V_NOM = the specified output voltage
• V_PRE = output voltage measured at 25°C pre-temperature cycling
• V_POST = 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.

Typical thermal hysteresis distribution is as shown in Figure 8-4 and Figure 8-5.

Figure 8-4 Thermal Hysteresis Distribution Cycle 1 (V_OUT)

Figure 8-5 Thermal Hysteresis Distribution Cycle 2 (V_OUT)