CapSense Technology
AN66308 - CY8CMBR2044 CapSense® Design Guide, Doc. No. 001-66308 Rev. *F
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SmartSense Auto-Tuning
Tuning the touch-sensing user interface is a critical step in ensuring proper system operation and a pleasant user
experience. In the typical design flow, the button interface is tuned in the initial design phase, during system
integration, and before the
production ramp. Because it’s an iterative process, tuning can be time-consuming.
SmartSense Auto-Tuning was developed to simplify the user interface development cycle. It is easy to use and
reduces the design cycle time by eliminating the hassles of further manual tuning in prototype and manufacturing
stages. SmartSense Auto-Tuning tunes each CapSense button automatically at power up and then monitors and
maintains optimum button performance during runtime. This technology adapts for manufacturing variation in PCBs
and overlays and automatically tunes out noise from sources such as LCD inverters, AC lines, and switch-mode
power supplies.
Process Variation
SmartSense Auto-Tuning for the CY8CMBR2044 is designed to work with button parasitic capacitance in the range of
5 pF to 40 pF, (typical button C
P
values range from 10 pF to 20 pF). The sensitivity parameter for each button is set
automatically, based on the characteristics of that particular button. The parameter improves the yield in mass
production because every button maintains a consistent response regardless of the C
P
variation (from 5 pF to 40 pF)
between the buttons. Parasitic capacitance of the individual buttons can vary due to PCB layout and trace length,
PCB manufacturing process variation, or vendor-to-vendor PCB variation within a multi-sourced supply chain. The
sensitivity of a button depends on its parasitic capacitance; higher C
P
values decrease sensitivity, resulting in
decreased finger touch signal amplitude. In some cases, a change in C
P
detunes the system, resulting in unfavorable
button performance (either too sensitive or insensitive) or even a nonoperational button. In either situation, you must
retune the system and, in some cases, you need to requalify the user interface subsystem. SmartSense Auto-Tuning
resolves these issues.
SmartSense Auto-Tuning makes platform designs possible. For example, consider the capacitive touch sensing
multimedia keys on a laptop computer; the spacing between the buttons depends on the size of the laptop and the
keyboard layout. In this example, the wide-screen machine has larger spaces between the buttons than a standard-
screen model would. The additional space means increased trace length between the button and the CapSense
controller. The bigger trace length, in turn, leads to a higher parasitic capacitance of the button. As a result, the
parasitic capacitance of the CapSense buttons can vary in different models of the same platform design. Though the
buttons’ functionality is identical for all of the laptop models, the buttons must be tuned for each model. SmartSense
Auto-Tuning lets you do platform designs using the recommended practices shown in the PCB Layout in
Figure 2-5. Design of Laptop Multi-Media Keys for 21-inch Model
Figure 2-6. Design of Laptop Multi-Media Keys for 15-inch Model with Same Functionality and Button Size
Reduced Design Cycle Time
When you design a capacitive button interface, the most time-consuming tasks are firmware development, layout,
and button tuning. With a typical touch-sensing controller, the button must be retuned when the same design is
ported to different models or when the mechanical dimensions change in the PCB or the button PCB layout. A design
with SmartSense
™ Auto-Tuning meets these challenges because it needs no firmware development, no manual
tuning, and no retuning.
In addition, SmartSense™ Auto-Tuning speeds up a typical design cycle.
compares the design cycles of a typical touch-sens
ing controller and a SmartSense™ Auto-Tuning-based design.
