Abstract

Polymer-based relative humidity sensors can exhibit a recoverable shift in RH error after prolonged exposure to high-humidity conditions. This shift in RH error from the time-zero RH is called RH drift. In systems that cannot rely on passive recovery at normal room conditions or offline oven baking, an integrated heater provides a practical in-system method to accelerate moisture removal from the sensing element and reduce RH offset. This application note addresses two design cases: one-shot recovery after an isolated high-humidity event and periodic mitigation during sustained high-humidity operation. On the 62-mil rigid FR4 HDC3020 board evaluated here, with the thermal pad soldered, one second of full-power heating every minute at 3.3V delivered the best balance among the tested continuous schedules, holding final RH drift near +0.18 %RH. Heater effectiveness improves when PCB thermal mass is reduced, thermal resistance to the environment is increased, and heater power is increased. However, those gains in heater performance must be balanced against power consumption.

Figure 1-1 Continuous and One-Shot RH Drift Mitigation