Datasheet

CY8C21x34/B CapSense
®
Design Guide Document No. 001-66271 Rev. *B 5
5.1
Overlay Selection ................................................................................................................................................ 37
5.2 ESD Protection .................................................................................................................................................... 38
5.2.1 Prevent ................................................................................................................................................... 38
5.2.2 Redirect .................................................................................................................................................. 38
5.2.3 Clamp ..................................................................................................................................................... 38
5.3 Electromagnetic Compatibility (EMC) Considerations ......................................................................................... 38
5.3.1 Radiated Interference ............................................................................................................................. 38
5.3.2 Radiated Emissions ................................................................................................................................ 39
5.3.3 Conducted Immunity and Emissions ....................................................................................................... 39
5.4 Software Filtering ................................................................................................................................................. 39
5.5 Power Consumption ............................................................................................................................................ 40
5.5.1 System Design Recommendations ......................................................................................................... 40
5.5.2 Sleep-Scan Method ................................................................................................................................ 40
5.5.3 Response Time versus Power Consumption .......................................................................................... 41
5.5.4 Measuring Average Power Consumption ............................................................................................... 41
5.6 Pin Assignments .................................................................................................................................................. 42
5.7 PCB Layout Guidelines ....................................................................................................................................... 42
6. Water Tolerance ........................................................................................................................................................... 43
6.1 Shield Electrode and Guard Sensor .................................................................................................................... 43
6.1.1 Shield ...................................................................................................................................................... 43
6.1.2 Guard Sensor ......................................................................................................................................... 46
6.2 Design Recommendations .................................................................................................................................. 48
7. Proximity Sensing ....................................................................................................................................................... 49
7.1 Types of Proximity Sensors ................................................................................................................................. 49
7.1.1 Button ..................................................................................................................................................... 49
7.1.2 Wire ........................................................................................................................................................ 49
7.1.3 PCB Trace .............................................................................................................................................. 49
7.1.4 Sensor Ganging ...................................................................................................................................... 49
7.2 Design Recommendations .................................................................................................................................. 50
8. Low Power Design Considerations ............................................................................................................................ 51
8.1 Additional Power Saving Techniques .................................................................................................................. 51
8.1.1 Set Drive Modes to Analog HI-Z ............................................................................................................. 51
8.1.2 Putting it All Together ............................................................................................................................. 52
8.1.3 Sleep Mode Complications ..................................................................................................................... 52
8.1.4 Pending Interrupts .................................................................................................................................. 52
8.1.5 Global Interrupt Enable ........................................................................................................................... 52
8.2 Post Wakeup Execution Sequence ..................................................................................................................... 53
8.2.1 PLL Mode Enabled ................................................................................................................................. 53
8.2.2 Execution of Global Interrupt Enable ...................................................................................................... 53
8.2.3 I
2
C Slave with Sleep Mode ..................................................................................................................... 53
8.2.4 Sleep Timer ............................................................................................................................................ 53
9. Resources .................................................................................................................................................................... 55