CapSense Performance Tuning with User Modules
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
38
C
P
(pF)
Precharge Source = PRS
Precharge Source = Prescaler
Prescaler
IMO = 24 MHz
Prescaler
IMO = 12 MHz
Prescaler
IMO = 6 MHz
Prescaler
IMO = 24 MHz
Prescaler
IMO = 12 MHz
Prescaler
IMO = 6 MHz
38
–41
8
4
2
16
8
4
42
–45
8
4
2
16
8
4
46
–49
8
4
2
16
8
4
50
–52
8
4
2
16
8
4
53
–56
8
4
2
16
8
4
57
–60
8
4
2
16
8
4
Note 1
This combination of Precharge Source, Prescaler, and C
P
is not recommended.
4.2.8 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 2
N
-1.
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
depends on overlay thickness, sensor size, and proximity of the
sensor to other large conductors.
F
values as a function of overlay thickness and circular sensor
diameter.
Figure 4-4. Finger Capacitance (C
F
) Based on Overlay Thickness and Circular Sensor Diameter
Table 4-2. Resolution Setting Based on Finger Capacitance and C
P
C
P
(pF)
C
F
= 0.1 pF
C
F
= 0.2 pF
C
F
= 0.4 pF
C
F
= 0.8 pF
<6
11
10
9
8
7
–12
12
11
10
9
13
–24
13
12
11
10
25
–48
14
13
12
11
>49
15
14
13
12
4.2.9 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
