Design Considerations
AN64846 - Getting Started with CapSense
®
Doc. No. 001-64846 Rev. *X
83
3.8.12 Ground Plane
Ground fill is added to both the top and bottom of the sensing board. When ground fill is added near a CapSense sensor
pad, there is a tradeoff between maintaining a high level of CapSense signal and increasing the noise immunity of the
system. Typical hatching for the ground fill is 25 percent on the top layer (7 mil line, 45 mil spacing) and 17 percent on
the bottom layer (7-mil line, 70-mil spacing).
Figure 3-69. Recommended Button and Slider Layout Top Layer
Figure 3-70. Recommended Button and Slider Layout Bottom Layer
3.8.13 Power Supply Layout Recommendations
A poor PCB layout would introduce noise in high-sensitivity sensors (e.g., proximity sensors and button sensors that
use overlays thicker than 1 mm). To achieve low noise on high-sensitivity CapSense sensors in designs, it is important
that the PCB layout follows the best practices on power supply trace and placement.
1. Two decoupling capacitors must be connected between the VDD and VSS pins. (Capacitor specification: 0.1 µF
and 1 µF, 16 V, Ceramic, X7R).
2. One decoupling capacitor must be connected between the VCC and VSS pins for CY8CMBR3XXX devices.
(Capacitor specification: 0.1 µF, 16 V, Ceramic, X7R).
3. When using packages E-pad (paddle), it must be connected to the board GND.
4. The decoupling capacitors and CMOD capacitor must be connected as close as possible to the chip to keep
impedance of the ground and supply traces as low as possible.
