The HDC3120 is an analog output sensor that incorporates both humidity-sensing and temperature-sensing elements in a 2.50mm × 2.50mm, 8-pin WSON package. The output voltages of the HDC3120 are linearly proportional to the measured relative humidity and temperature. Both the temperature and humidity sensors are 100% tested and trimmed on a production setup that is NIST traceable and verified with equipment that is calibrated to ISO/IEC 17025 standards.

The device provides excellent measurement accuracy at very low power, consuming only 230μA during typical normal operation, and supports wide supply range of 1.62V to 5.5V. The device also features a RESET_EN pin that can be toggled low to keep the device in a low power state to reduce overall power consumption of the system. Upon releasing the RESET_EN pin, the device performs a complete reset before measurements are restarted.

Figure 7-1 Capacitor With Polymer Dielectric

The HDC3120 measures relative humidity through variations in the capacitance of a polymer dielectric. The sensor consists of two conductive electrodes that adjoin a thin film polymer dielectric (see Figure 7-1). As humidity increases, the polymer begins to absorb water molecules from the surrounding (air) environment, which alters the dielectric constant of the capacitor sensor. The relationship between the capacitance and relative humidity is used to determine the humidity level.

As with most relative humidity sensors that include this type of technology, care must be taken to provide best device performance. This includes:

• Follow the correct storage and handling guidelines to provide the performance of the HDC3120 as specified. Special care must be taken to avoid chemical contamination or damage to the sensor during assembly, storage, or operation. See Section 8.6.1 and HDC3x Silicon User's Guide for these guidelines.

• Reduce prolonged exposure to both high temperature and humidity extremes that can impact sensor accuracy.

• Follow the correct layout guidelines for best performance. See Section 8.5.1and Optimizing Placement and Routing for Humidity Sensors application note for these guidelines.
• Rehydration is required for polymer based humidity sensor like the HDC3120. Rehydration restores the baseline performance of the humidity sensor after high-temperature exposure, such as solder reflow.