User guide

4 Document No. 001-64846 Rev. *A Getting Started with CapSense®
3.
Design Considerations ............................................................................................................................................... 29
3.1 Overlay Selection ................................................................................................................................................ 29
3.1.1
Relationship to CapSense Signal Strength ............................................................................................. 29
3.1.2 Bonding Overlay to PCB ......................................................................................................................... 30
3.2
ESD Protection .................................................................................................................................................... 30
3.2.1 Preventing ESD Discharge ..................................................................................................................... 30
3.2.2
Redirect .................................................................................................................................................. 31
3.2.3 Clamp ..................................................................................................................................................... 31
3.3
Electromagnetic Compatibility (EMC) Considerations ......................................................................................... 32
3.3.1 Radiated Interference ............................................................................................................................. 32
3.3.2
Radiated Emissions ................................................................................................................................ 35
3.3.3 Conducted Immunity and Emissions ....................................................................................................... 36
3.4
Software Filtering ................................................................................................................................................. 37
3.4.1 Average Filter ......................................................................................................................................... 37
3.4.2
IIR Filter .................................................................................................................................................. 39
3.4.3 Median Filter ........................................................................................................................................... 40
3.4.4
Jitter Filter ............................................................................................................................................... 42
3.4.5 Event Based Filter .................................................................................................................................. 44
3.4.6
Rule Based Filter .................................................................................................................................... 44
3.5 Power Consumption ............................................................................................................................................ 44
3.5.1
Active and Sleep Current ........................................................................................................................ 44
3.5.2 Average Current ..................................................................................................................................... 44
3.5.3
Response Time vs. Power Consumption ................................................................................................ 45
3.6 Pin Assignments .................................................................................................................................................. 46
3.7
PCB Layout Guidelines ....................................................................................................................................... 48
3.7.1 Parasitic Capacitance, C
P
...................................................................................................................... 48
3.7.2
Board Layers .......................................................................................................................................... 48
3.7.3 Board Thickness ..................................................................................................................................... 48
3.7.4
Button Design ......................................................................................................................................... 49
3.7.5 Slider Design .......................................................................................................................................... 49
3.7.6
Sensor and Device Placement ............................................................................................................... 50
3.7.7 Trace Length and Width ......................................................................................................................... 50
3.7.8
Trace Routing ......................................................................................................................................... 50
3.7.9 Crosstalk Solutions ................................................................................................................................. 51
3.7.10
Vias ......................................................................................................................................................... 52
3.7.11 Ground Plane ......................................................................................................................................... 52
3.7.12 Shield Electrode and Water Tolerance ................................................................................................... 53
4.
CapSense Product Portfolio ....................................................................................................................................... 55
4.1 Cypress’s CapSense Controller Solutions ........................................................................................................... 55
4.1.1
CapSense Express Controllers (Configurable Solutions) ....................................................................... 55
4.1.2 CapSense Controllers (Programmable Solutions) .................................................................................. 55
4.1.3
CapSense Plus (Programmable Solutions) ............................................................................................ 56
5. CapSense Selector Guide ........................................................................................................................................... 57
5.1
Selecting the Right CapSense Device ................................................................................................................. 57
6. CapSense Migration Paths ......................................................................................................................................... 60
6.1
CY8C20x34 to CY8C20xx6A/H ........................................................................................................................... 60