Proper PCB layout of the HDC302x is critical to obtaining accurate measurements
of temperature and relative humidity. Therefore, TI recommends to:
- Isolate all heat sources from the HDC302x.
This means positioning the HDC302x away from power
intensive board components such as a battery, display, or micrcocontroller.
Ideally, the only onboard component close to the HDC302x is the supply bypass capacitor. See the Layout Example for more information.
- Eliminate copper layers below the device (GND,
VDD).
- Use slots or a cutout around the device to reduce the thermal
mass and obtain a quicker response time to sudden environmental changes.
- The diameter of the
cutout around the part in this case is approximately 6 mm. The important
details are to implement a separation of thermal planes while allowing
for power, ground and data lines and place the part on the board, while
still meeting mechanical assembly requirements. In addition to the
Layout Example, other representations of cutouts for thermal relief can be
found in Optimizing Placement and Routing for
Humidity Sensors section 2.3.
- Follow the Example Board Layout and Example Stencil Design that
is illustrated in Mechanical, Packaging, and Orderable Information.
- The SCL and the SDA
lines require pull up resistors and TI recommends to connect a 0.1-uF
cap to the VDD line.
- TI recommends a
multilayer ceramic bypass X7R capacitor of 0.1 μF between the VDD and
GND pins.
- It is generally best practice to solder the package thermal pad
to a board pad that is connected to ground, however to minimize thermal mass for
maximum heater efficiency or to measure ambient temperature it may be left
floating. Floating the thermal pad is an option because the thermal pad has a
non-conductive epoxy. See HDC3x Silicon User's
Guide for more information regarding when leaving the thermal pad
floating may be helpful for your application.