Datasheet

CY8C20xx6A/H CapSense Design Guide Doc. No. 001-65973 Rev. *A 45
5.5.4 Measuring Average Power Consumption
The following instructions describe how to determine average power consumption when using the sleep-scan
method:
1. Build a project that scans all of the sensors without going to sleep (continuous-scan mode). Include a pin-toggle
feature in the code before scanning the sensors. Toggling the state of the output pin serves as a time marker that
can be tracked with an oscilloscope.
2. Download the project to the CapSense device and measure the current consumption. Assign the measured
current to I
Act
3. Get the sleep current information from the datasheet and assign it to I
.
Slp
4. Monitor the toggling output pin in the oscilloscope and measure the time period between two toggles. This gives
the active time. Assign this value to t
.
Act
5. Apply sleep-scan to the project. The time period of the sleep-scan cycle, T, is set by selecting the sleep timer
frequency in the global resources window as shown in
.
Figure 5-1.
6. Subtract active time from the sleep-scan cycle time period to get the sleep time. t
Slp
= T - t
Act
7. Calculate the average current using Equation 13.
.
8. Calculate average power consumption using Equation 14.
Figure 5-1. Global Resources Window
5.6 Pin Assignments
An effective method to reduce interaction between CapSense sensor traces and communication and non-CapSense
traces is to isolate each by port assignment. Figure 5-2 shows a basic version of this isolation for a 32-pin QFN
package. Because each function is isolated, the CapSense controller is oriented such that there is no crossing of
communication, LED, and sensing traces.
Figure 5-2. Recommended: Port Isolation for Communication, CapSense and LEDs