Datasheet

CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 12
2.2.4 SmartSense™ Auto-Tuning
Tuning the touch sensing user interface is a critical step in ensuring proper system operation and a pleasant user
experience. The typical design flow entails tuning the sensor interface in the initial design phase, during system
integration, and finally production fine-tuning before the production ramp. Tuning is an iterative process and can be
time consuming. SmartSense Auto-Tuning was developed to simplify the user interface development cycle. It is easy
to use and significantly reduces the design cycle time by eliminating the tuning process throughout the entire product
development cycle, from prototype to mass production. SmartSense tunes each CapSense sensor automatically at
power up and then monitors and maintains optimum sensor performance during run time. This technology adapts for
manufacturing variation in PCBs, overlays and noise generators such as LCD inverters, AC line noise, and switch-
mode power supplies, and automatically tunes them out.
2.2.4.1 Process Variation
The SmartSense User Module (UM) for the CY8C20xx6A/H is designed to work with sensor parasitic capacitance in
the range of 5 pF to 45 pF, (typical sensor C
P
values are in the range of 10 pF to 20 pF). The sensitivity parameter for
each sensor is set automatically, based on the characteristics of that particular sensor. This improves the yield in
mass production, because consistent response is maintained from every sensor regardless of C
P
variation between
sensors within the specified range of 5 to 45 pF. Parasitic capacitance of the individual sensors can vary due to PCB
layout, PCB manufacturing process variation, or with vendor-to-vendor PCB variation within a multisourced supply
chain. The sensitivity of a sensor depends on its parasitic capacitance; higher C
P
values will decrease the sensor
sensitivity and result in decreased finger touch signal amplitude. In some cases, the change in C
P
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 spacing 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 the system designer to do
platform designs using the recommended best practices shown in section 3.7 PCB Layout in
value will detune
the system, resulting in less than optimum sensor performance (either too sensitive or not sensitive enough) or worst
case, a nonoperational sensor. In either situation, you must retune the system, and in some cases requalify the UI
subsystem. SmartSense Auto-Tuning solves these issues.
Getting Started with
CapSense, knowing the tuning will be done efficiently and automatically.
Figure 2-8. Design of Laptop Multimedia Keys for a 21-inch Model
Figure 2-9. Design of Laptop Multimedia Keys for a 15-inch model with Identical Functionality and Button Size
2.2.4.2 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 since it needs less firmware development effort, no tuning, and no
retuning. This makes a typical design cycle much faster. Figure 2-10 compares the design cycles of a typical touch-
sensing controller and a SmartSense-based design.