Datasheet

CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 8
2. CapSense Technology
2.1 CapSense Equivalent Model
Figure 2-1. CapSense System Equivalent Model
The capacitance measured by the CapSense controller is named C
X
. When a finger is not on the sensor, C
X
equals
the parasitic capacitance of the system, C
P.
When a finger touches the sensor surface, it forms a simple parallel plate
capacitor through the overlay with the sensor pad. The result is called finger capacitance, C
F


=






Equation 1
, and can be defined by
the following equation.
Where:
ε
0
ε
= Free space permittivity
r
A = Area of finger and sensor pad overlap
= Dielectric constant of overlay
D = Overlay thickness
With a finger on the sensor pad, C
X
equals the sum of C
P
and C
F


= 

+ 

Equation 2
:
2.2 CapSense Capacitive Sensing Methods
The CY8C20xx6A/H device family measures sensor capacitance using either the CSD or CSA_EMC methods. Both
of these methods require one additional capacitor, C
MOD
. The recommended value for C
MOD
is 2.2 nF with a minimum
5-V voltage rating and X7R or NPO types.