To further reduce power consumption, user interface backlighting can be turned off while the controller is in low report rate mode. Once a touch is detected, the backlighting can be turned back on while the controller is in fast report rate mode.
Use the priority rule to wake up from sleep mode
In some applications all buttons should not be able to wake the capacitive sensing controller from sleep mode.
For example, when a TV is turned off, the controller only needs to detect a finger touch on the power button to turn the TV on. In this application, when the power is off the controller only samples the power button and does not sample any of the other buttons on the TV’s front panel. This reduces TActive
, and significantly reduces average power consumption.
Let’s take a look at typical TV front panel:
. Eight capacitive touch sensing buttons
. Sampling time = 500 µs per button
= 4 mA
= 10 ms
= 1 µA
= 90 ms
, when all buttons are sampled:
= 160 µA
When only the power button is sampled:
= 20 µA
In the second part of this article, I will discuss other methods of optimizing average power in capacitive touch sensing designs such as:
- Using a ganged capacitive sensor method to wake up from sleep mode
- Using a proximity sensor to wake up from sleep mode
- Using an external regulator to turn off power
- Using the low power option specific to the capacitive sensing controller
About the author
Vibheesh B is a Senior Applications Engineer working in Cypress Semiconductor’s Consumer and Computation Division and has specialized on Capacitive Touch Sensing applications since 2007. His responsibilities include defining technical requirements for new capacitive sensing controllers, developing new capacitive sensing controllers, conducting system analysis, debugging technical issues for customers, technical writing, and failure-analysis debugging.
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