Cypress CY8C20xx7/S CapSense Series, Design Manual

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Contents
CY8C20xx7/S CapSense
®
Design Guide Doc. No. 001-78329 Rev. *E 4
4.2.2 I
DAC
Range .................................................................................................................................... 37
4.2.3 Autocalibration .............................................................................................................................. 37
4.2.4 I
DAC
Value ..................................................................................................................................... 37
4.2.5 Compensation I
DAC
Value ............................................................................................................. 37
4.2.6 Precharge Source ......................................................................................................................... 37
4.2.7 Prescaler ...................................................................................................................................... 37
4.2.8 Resolution ..................................................................................................................................... 38
4.2.9 Scanning Speed ........................................................................................................................... 38
4.2.10 High-Level API Parameters .......................................................................................................... 39
4.2.11 Set High-Level Parameters ........................................................................................................... 40
4.3 Using the SmartSense_EMCPLUS User Module ...................................................................................... 40
4.3.1 Guidelines for SmartSense_EMC_PLUS ...................................................................................... 40
4.3.2 Understanding the Difference ....................................................................................................... 40
4.3.3 Recommended C
MOD
Value for SmartSense_EMC_PLUS ........................................................... 41
4.3.4 SmartSense_EMCPLUS User Module Parameters ...................................................................... 41
4.3.5 SmartSense_EMCPLUS User Module Specific Guidelines .......................................................... 41
4.3.6 Scan Time of a CapSense Sensor................................................................................................ 42
4.3.7 SmartSense_EMCPLUS Response Time ..................................................................................... 43
4.3.8 Method to Ensure Minimum SNR Using the SmartSense_EMCPLUS UM ................................... 44
4.3.9 Firmware Design Guidelines ......................................................................................................... 45
4.4 Design Migration from CY8C20xx6A/AS to CY8C20xx7/S ........................................................................ 47
4.4.1 Discontinued Support/User Modules ............................................................................................ 47
4.4.2 Improvement and New Features................................................................................................... 47
4.4.3 Pin Compatibility ........................................................................................................................... 47
5. Design Considerations ..................................................................................................................................... 48
5.1 Overlay Selection ...................................................................................................................................... 48
5.2 ESD Protection .......................................................................................................................................... 49
5.2.1 Prevent ......................................................................................................................................... 49
5.2.2 Redirect ........................................................................................................................................ 49
5.2.3 Clamp ........................................................................................................................................... 49
5.3 Electromagnetic Compatibility (EMC) Considerations ............................................................................... 49
5.3.1 Radiated Interference ................................................................................................................... 49
5.3.2 Radiated Emissions ...................................................................................................................... 50
5.3.3 Conducted Immunity and Emissions ............................................................................................. 50
5.4 Software Filtering ....................................................................................................................................... 50
5.5 Power Consumption .................................................................................................................................. 51
5.5.1 System Design Recommendations ............................................................................................... 51
5.5.2 Sleep-Scan Method ...................................................................................................................... 51
5.5.3 Response Time versus Power Consumption ................................................................................ 51
5.5.4 Measuring Average Power Consumption ..................................................................................... 52
5.6 Pin Assignments ........................................................................................................................................ 52
5.7 GPIO Load Transient ................................................................................................................................. 53
5.7.1 Hardware Guidelines to Reduce GPIO Load Transient Noise ...................................................... 54
5.7.2 Firmware Guidelines to Compensate GPIO Load Transient Noise ............................................... 55
5.8 PCB Layout Guidelines ............................................................................................................................. 57
6. Liquid-Tolerant Design Considerations .......................................................................................................... 58