User guide
Getting Started with CapSense Document No. 001-64846 Rev. *A 45
The average current consumed by the device over a long time period can be calculated by using the following
equation.
=
(
×
)
(
×
)
Equation 20
The average power consumed by the device can be calculated as follows:
=
×
Equation 21
3.5.3 Response Time vs. Power Consumption
As illustrated in Equation 12, the average power consumption can be reduced by decreasing I
AVE
or V
DD
. I
AVE
In any application, if both power consumption and response time are important parameters to be considered, then, an
optimized method can be used which incorporates both continuous-scan and sleep-scan modes. In this method the
device spends most of its time in sleep-scan mode where it scans the sensors and goes to sleep periodically as
explained in the previous section and thereby consuming less power. When user touches a sensor to operate the
system, the device jumps to continuous-scan mode where the sensors are scanned continuously without invoking
sleep and thereby giving very good response time. The device remains in continuous-scan mode for a specified time-
out period. If the user does not operate any sensor within this time-out period, the device jumps back to the sleep-
scan mode.
may be
decreased by increasing sleep time. Increasing sleep time to a very high value will lead to poor response time of the
CapSense button. Because of this tradeoff between response time and power consumption, the application developer
has to carefully select the sleep time based on system requirements.