CY8CKIT-030 PSoC® 3 Development Kit Guide, Doc. # 001-61038 Rev. *J
56
Appendix
A.5
Using RBLEED Resistor for CapSense
An RBLEED resistor value of 2.2 K provides good SNR values for the onboard CapSense buttons
and sliders. However, tuning CapSense with a fixed RBLEED value is difficult because the analog
switch divider and scan resolution are the only tunable parameters.
For onboard CapSense buttons and sliders, with RBLEED of 2.2 K, the following SNR is achieved.
If RBLEED is used for CapSense, remember the following:
■
Use RBLEED only if all IDACs in the device are used for other purposes. IDAC sourcing/sinking
method is recommended because it provides better flexibility and automatic tuning feature.
■
Use multiple RBLEED resistors if there are different types of sensors in the design. PSoC 3 and
PSoC 5 supports up to three RBLEED resistors per channel.
■
Use variable resistors for RBLEED, for better tunability.
Sensor
Parameter
Value
Button 0
Analog Switch Divider
2
Scan Resolution
10 bits
SNR
74
Button 1
Analog Switch Divider
3
Scan Resolution
10 bits
SNR
76
Linear Slider, Element 0
Analog Switch Divider
2
Scan Resolution
10 bits
SNR (individual sensor)
85
Linear Slider, Element 1
Analog Switch Divider
2
Scan Resolution
10 bits
SNR (individual sensor)
85
Linear Slider, Element 2
Analog Switch Divider
2
Scan Resolution
10 bits
SNR (individual sensor)
85
Linear Slider, Element 3
Analog Switch Divider
2
Scan Resolution
10 bits
SNR (individual sensor)
85
Linear Slider, Element 4
Analog Switch Divider
2
Scan Resolution
10 bits
SNR (individual sensor)
85
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