Datasheet

40 Document No. 001-66271 Rev. *B CY8C21x34/B CapSense
®
Design Guide
Table 5-4 shows the RAM and flash requirements for different software filters. The amount of flash required for each
filter type depends on the performance of the compiler. The requirements listed here are for both the ImageCraft
compiler and the ImageCraft Pro compiler
Table 5-4. RAM and Flash Requirements
Filter Type Filter Order RAM
(Bytes per
sensor)
Flash (Bytes)
ImageCraft
Compiler
Flash (Bytes)
ImageCraft Pro
Compiler
Average 2-8 6 675 665
IIR 1 2 429 412
2 6 767 622
Median 3 6 516 450
5 10 516 450
Jitter filter on Raw Counts N/A 2 277 250
Jitter filter on slider centroid N/A 2 131 109
A code example that uses all of the filters listed above can be downloaded here.
5.5 Power Consumption
5.5.1 System Design Recommendations
For many designs, minimizing power consumption is an important goal. There are several ways to reduce the power
consumption of your CapSense capacitive touch-sensing system.
 Set GPIO drive mode for low power
 Turnoff high power blocks
 Optimize CPU speed for low power
 Operate at a lower V
DD
In addition to these methods, applying the sleep-scan method can be very effective.
5.5.2 Sleep-Scan Method
In typical applications, the CapSense controller does not always need to be in the active state. The device can be put
into the sleep state to stop the CPU and the major blocks of the device. Current consumed by the device in sleep
state is much lower than the active current.
The average current consumed by the device over a long time period can be calculated by using the following
equation.
Equation 11
Where:
I
ACT
= active current
T
ACT
= active time
I
Slp
= sleep current
t
Slp
= seep time
T = total time period