Datasheet
CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 33
Idac Range
For projects where the maximum sensor C
P
Autocalibration
is less than 45 pF, use 4X; otherwise, use 8X.
Autocalibration should always be set to Enabled in CY8C20xx6A CSD designs. The ability of the autocalibration
algorithm to successfully set the iDAC relies on the prescaler being set properly and that C
MOD
iDAC Value
be of the
recommended size.
This parameter determines the current output of iDAC when autocalibration is disabled. When autocalibration is
enabled, as recommended, this parameter is overridden and has no effect. When autocalibration is disabled, raising
this parameter lowers the raw count baseline and vice versa.
Precharge Source
This parameter selects the sensor switching clock source. The available options are Prescaler, which uses the IMO
through a divider, or PRS, which passes the divided IMO clock through a pseudo random generator, providing a
spread-spectrum clock. PRS provides superior noise immunity and lower noise emissions and is therefore the
recommend default setting for Precharge Source. In some instances, the prescaler precharge source can provide
higher SNR (signal-to-noise ratio). However, when using copper circuitry, this SNR improvement is usually marginal
and rarely justifies foregoing the benefits of PRS.
Prescaler
Prescaler is the divider applied to the IMO to develop the precharge clock. This is the most critical hardware UM
parameter for properly tuning a CSD design. Prescaler depends on the selected precharge source, IMO, and the C
P
Table 4-1
of the sensors being scanned. provides recommended prescaler settings based on these parameters.
Table 4-1. Prescaler Setting Based on Precharge Source, IMO, and C
P
C
P
Precharge Source = PRS (pF) 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
<6 1 Note 1 Note 1 2 1 1
7–11 2 1 Note 1 4 2 1
12–15 2 1 Note 1 4 2 1
16–19 4 2 1 8 4 2
20–22 4 2 1 8 4 2
23–26 4 2 1 8 4 2
27–30 4 2 1 8 4 2
31–34 4 2 1 8 4 2
35–37 8 4 2 16 8 4
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.