Datasheet

CY8C21x34/B CapSense
®
Design Guide Document No. 001-66271 Rev. *B 15
SmartSense Auto-tuning makes platform designs possible. Imagine the capacitive touch sensing multimedia keys in a
laptop computer; the spacing between the buttons depends on the size of the laptop and keyboard layout. In this
example, the wide-screen machine has larger spaces between the buttons than a standard-screen model. More
space between buttons means increased trace length between the sensor and the CapSense controller, which leads
to higher parasitic capacitance of the sensor. This means that the parasitic capacitance of the CapSense buttons can
be different in different models of the same platform design. Though the functionality of these buttons is the same for
all of the laptop models, the sensors must be tuned for each model. SmartSense enables you to do platform designs
using the recommended best practices shown in the PCB Layout in Getting Started with CapSense, knowing the
tuning will be done efficiently and automatically.
Figure 2-5. Design of Laptop Multimedia Keys for a 21-inchModel
Figure 2-6. Design of Laptop Multimedia Keys for a 15-inchModel with Identical Functionality and Button Size
2.2.3.2 Reduced Design Cycle Time
Usually the most time-consuming task for a capacitive sensor interface design is firmware development and sensor
tuning. With a typical touch-sensing controller, the sensor must be retuned when the same design is ported to
different models or when there are changes in the mechanical dimensions of the PCB or the sensor PCB layout. A
design with SmartSense solves these challenges because it needs less firmware development effort, no tuning, and
no retuning. This makes a typical design cycle much faster. Figure 2-7 compares the design cycles of a typical touch-
sensing controller and a SmartSense-based design.
Figure 2-7. Typical Capacitive Interface Design Cycle Comparison
Feasibility
Study
Schematics
Design
PCB Layout
Design
Mechanical Design
Review
System
Integration
Re-tuning for any
changes
Tuning process
Production Fine
Tuning
Design
Validation
Production
Typical capacitive user interface Design Cycle
Firmware
Development
Feasibility
Study
Schematics
Design
PCB Layout
Design
Mechanical Design
Review
System
Integration
Design
Validation
Production
SmartSense based capacitive user interface Design Cycle
Firmware
Development