Datasheet

CY8C21x34/B CapSense
®
Design Guide Document No. 001-66271 Rev. *B 11
2. CapSense Technology
2.1 CapSense Fundamentals
CapSense is a touch-sensing technology that works by measuring the capacitance of each I/O pin on the CapSense
controller that has been designated as a sensor. As shown in Figure 2-1, the total capacitance on each of the sensor
pins can be modeled as equivalent lumped capacitors with values of C
X,1
through C
X,n
for a design with n sensors.
Circuitry internal to the CY8C21x34/B device converts the magnitude of each C
X
into a digital code that is stored for
post processing. The other components, namely Rb and C
MOD
, are used by the CapSense controller’s internal
circuitry.
Figure 2-1. CapSense Implementation in a CY8C21x34/B PSoC Device
CY8C21x34/B Rb
Cmod
Cx,n
Cx,2
Cx,1
Sensor Equivalent
Capacitors
P1[1] or P1[5]
P0[1] or P0[3]
As shown in Figure 2-2, each sensor I/O pin is connected to a sensor pad by traces, vias, or both as necessary. The
overlay is a nonconductive cover over the sensor pad that constitutes the product’s touch interface. When a finger
comes into contact with the overlay, the conductivity and mass of the body effectively introduces a grounded
conductive plane parallel to the sensor pad. This is represented in Figure 2-2. This arrangement constitutes a parallel
plate capacitor whose capacitance is given by Equation 1.
.