Datasheet

42 Document No. 001-66271 Rev. *B CY8C21x34/B CapSense
®
Design Guide
5.6 Pin Assignments
An effective method to reduce interaction between CapSense sensor traces and communication and non-CapSense
traces is to isolate each by port assignment. Figure 5-2 shows a basic version of this isolation for a 32-pin QFN
package. Because each function is isolated, the CapSense controller is oriented such that there is no crossing of
communication, LED, and sensing traces.
Figure 5-2. Recommended: Port Isolation for Communication, CapSense, and LEDs
CapSense controller architecture requires a current budget for even and odd port pin numbers. If the current budget
for odd port pin numbers is 100 mA, the total current drawn though all odd port pins should not exceed 100 mA. In
addition to the current budget limitation, there is also maximum current limitation for each port pin defined in the
CapSense controller datasheet.
All CapSense controllers provide high current sink and source capable port pins. When using high current sink or
source from port pins, you should use the ports that are closest to device ground pin to minimize the noise.
5.7 PCB Layout Guidelines
Detailed PCB layout guidelines are available in Getting Started with CapSense.