Datasheet

4 Document No. 001-66271 Rev. *B CY8C21x34/B CapSense
®
Design Guide
3.6.6
Debounce ............................................................................................................................................... 22
3.6.7 Negative Noise Threshold ...................................................................................................................... 22
3.6.8 Low Baseline Reset ................................................................................................................................ 22
3.6.9 High Level Parameter Recommendations .............................................................................................. 22
3.7 CSD User Module Low-Level Parameters ........................................................................................................... 23
3.7.1 Scanning Speed ..................................................................................................................................... 23
3.7.2 Resolution ............................................................................................................................................... 23
3.7.3 Reference ............................................................................................................................................... 24
3.7.4 Ref Value ................................................................................................................................................ 24
3.7.5 Prescaler Period ..................................................................................................................................... 24
3.7.6 Shield Electrode Out ............................................................................................................................... 24
3.8 CSDADC User Module Configurations ................................................................................................................ 24
3.8.1 CSDADC with PRS16 Clock Source....................................................................................................... 24
3.8.2 CSDADC with PRS8 Clock Source......................................................................................................... 24
3.8.3 CSDADC with PWM8 Clock Source ....................................................................................................... 25
3.8.4 CSDADC with VC2 Clock Source ........................................................................................................... 25
3.9 CSDADC User Module Parameters ..................................................................................................................... 25
3.10 Low-Level Parameters ......................................................................................................................................... 25
3.10.1 Scanning Speed ..................................................................................................................................... 25
3.10.2 Resolution ............................................................................................................................................... 25
3.10.3 Reference ............................................................................................................................................... 26
3.10.4 Ref Value ................................................................................................................................................ 26
3.10.5 Prescaler Period ..................................................................................................................................... 26
3.10.6 Shield Electrode Out ............................................................................................................................... 26
3.10.7 ADC Enabled .......................................................................................................................................... 26
3.11 SmartSense User Module Parameters ................................................................................................................ 27
3.12 Low-Level Parameters ......................................................................................................................................... 27
3.12.1 Shield Electrode Out ............................................................................................................................... 27
3.12.2 Modulator Capacitor Pin ......................................................................................................................... 27
3.12.3 Feedback Resistor Pin ............................................................................................................................ 27
3.12.4 Threshold Setting Mode .......................................................................................................................... 27
3.12.5 Sensitivity Level ...................................................................................................................................... 27
3.12.6 Finger Threshold..................................................................................................................................... 28
4. CapSense Performance Tuning with User Modules ................................................................................................. 29
4.1 General Considerations ....................................................................................................................................... 29
4.1.1 Signal, Noise, and SNR .......................................................................................................................... 29
4.1.2 Charge/Discharge Rate .......................................................................................................................... 30
4.1.3 Importance of Baseline Update Threshold Verification ........................................................................... 31
4.2 Tuning the CSD and CSDADC User Modules ..................................................................................................... 32
4.2.1 Set Up Hardware and Software for Tuning ............................................................................................. 33
4.2.2 Select Prescaler...................................................................................................................................... 33
4.2.3 Set Raw Count Range with R
b
................................................................................................................ 33
4.2.4 Set High-Level Parameters ..................................................................................................................... 34
4.3 Configuring SmartSense User Module ................................................................................................................ 34
5. Design Considerations ............................................................................................................................................... 37