User guide

Getting Started with CapSense Document No. 001-64846 Rev. *A 31
3.2.2 Redirect
If your product is densely packed, it may not be possible to prevent the discharge event. In this case you can protect
the CapSense controller by controlling where the discharge occurs. This can be achieved through a combination of
PCB layout, mechanical layout of the system, and conductive tape or other shielding material. A standard practice is
to place a guard ring on the perimeter of the circuit board. The guard ring should connect to chassis ground.
Figure 3-2. Guard Ring
CapSense
Controller
Ground with conductive
material on the perimeter to
direct discharge away from
CapSense controller
As recommended in PCB Layout Guidelines, providing a hatched ground plane around the button or slider sensor
can also redirect the ESD event away from the sensor and CapSense controller.
3.2.3 Clamp
Because CapSense sensors are purposely placed in close proximity to the touch surface, it may not be practical to
redirect the discharge path. In this case including series resistors or special purpose ESD protection devices may be
appropriate. Adding a series resistor on the vulnerable traces is a cost effective protection method. This technique
works by splitting the dissipation between the resistor and the controller. The recommended series resistance added
to the CapSense inputs is 560 ohms. More details can be found in the Series Resistor section.
Figure 3-3. ESD Protection Using a Series Resistor