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:
- 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.
Typical thermal hysteresis distribution is as
shown in Figure 8-4 and Figure 8-5.
Figure 8-4 Thermal Hysteresis
Distribution Cycle 1 (VOUT)
Figure 8-5 Thermal Hysteresis Distribution Cycle 2