Datasheet

CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 34
Resolution
Available choices are 9 to 16 bits. Raising the resolution raises sensitivity, SNR, and noise immunity at the expense
of scan time. The maximum raw count (full scale range) for scanning resolution n is 2n – 1. Table 4-2 provides
recommended resolution settings based on C
P
and the finger capacitance C
F
. C
F
is the change in capacitance of a
sensor when a finger is placed on the sensor. C
F
Figure 4-7
depends on overlay thickness, sensor size, and proximity of the
sensor to other large conductors. provides C
F
Figure 4-7. Finger Capacitance (C
values as a function of overlay thickness and circular sensor
diameter.
F
) Based on Overlay Thickness and Circular Sensor Diameter
Table 4-2. Resolution Setting Based on Finger Capacitance and C
P
C
P
C (pF)
F
C = 0.1 pF
F
C = 0.2 pF
F
C = 0. 4pF
F
<6
= 0.8 pF
12 11 10 9
7–12 13 12 11 10
13–24 14 13 12 11
25–48 15 14 13 12
>49 16 15 14 13
Scanning Speed
This parameter controls the integration time for each LSB of the scan result. The choices are Ultra Fast, Fast,
Normal, and Slow. Fast is generally a good starting point. In some, but not all cases, slower scanning speed can yield
higher SNR at the expense of longer scan time and more power consumption. Table 4-3 shows the actual scan time
in microseconds for a single sensor based on resolution and scanning speed.