Design Considerations
CY8C20xx7/S CapSense
®
Design Guide
Doc. No. 001-78329 Rev. *E
52
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 period of the sleep-scan cycle, T, is set by selecting the sleep timer
frequency in the global resources window as shown in
6. Subtract active time from the sleep-scan cycle period to get the sleep time. T
SLP
= T
– t
ACT
.
7. Calculate the average current using Equation 5-1.
8. Calculate average power consumption using Equation 5-2.
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.
shows a basic version of this isolation for a QFN package.
Because each function is isolated, the CapSense controller is oriented such that there is no crossing of
communication, LED, and sensing traces.
