Datasheet

CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 24
3.6.1 Settling Time
The Settling Time parameter controls the software delay that allows the voltage on the C
MOD
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Equation 5
capacitor to stabilize.
Each loop has nine CPU cycles per iteration. Select a settling Time based on Equation 5.
Where:
R
series
C
= 400-Ω + series resistor placed between port pin and sensor (typical value 560 Ω)
P
Possible values are 2 to 255.
= sensor base capacitance
3.6.2 Freq Num
This parameter improves EMC performance by implementing a patented EMC improvement technology.
Freq Num = 1 corresponds to the standard scanning algorithm and Freq Num = 3 turns on the advanced algorithm.
Enabling the advanced scanning algorithm increases the scanning time and RAM usage by a factor of three.
Possible values are 1 (standard scanning algorithm) and 3 (advanced algorithm).
3.6.3 Spread Spectrum
This parameter improves EMC performance by implementing a firmware-based spread-spectrum technique that
randomly changes the clock value during scanning. Spread spectrum is enabled when Freq Num is set to 1.
Possible values are 1 (enabled) and 3 (disabled).
3.6.4 Raw Data Median Filter
The median filter looks at the three most recent samples from a sensor and reports the median value. It is used to
remove short noise spikes. This filter generates a delay of one sample. This filter is generally not recommended
because of the delay and RAM usage. Enabling this filter consumes (Number of Sensors × 2 × Freq Num) bytes of
RAM and 100 bytes of Flash. It is disabled by default.
Possible values are Enabled and Disabled.
3.6.5 RawData IIR Filter
This infinite impulse response (IIR) filter reduces noise in the conversion result (raw count). Filtering on the raw
counts can be more effective than filtering the XY coordinate, but requires more RAM. Enabling this filter consumes
an additional 100 bytes of Flash. It is disabled by default. The default IIR coefficient is 0.5.
Possible values are Enabled and Disabled.
3.6.6 RawData IIR Filter Coefficient
This is the coefficient for the Raw Count IIR filter.
Possible values are 2 (½ previous sample + ½ current sample) and 4 (¾ previous sample + ¼ current sample).
3.6.7 Clock
The Clock parameter can be used to increase the amount of effective resistance of the sensor. If the sensor area is
large, the effective resistance may be too high for the autocalibration of the switched capacitor circuit. Large proximity
sensors may encounter decreased sensitivity. In this case, the settling voltage is too far below the comparator
threshold. Setting a larger divider of the internal main oscillator (IMO) increases the effective resistance,
compensating for the high capacitance.
Possible values are IMO, IMO/2, IMO/4, and IMO/8.