APPLICATION NOTE
RX113 G roup
Design G uide for Renesas Touch Solution
Summary
The RX113 group has incorporated hardware (Capacitive Touch Sensor Unit; CTSU) that detects human body
contact by measuring capacitance existed between touch electrode and human body.
This app lic a tion note introduces the p rinciple of capacitive touch dete c tion as well as explains the detail of current-
frequency conversion sys tem that is used in RX113.
Target Device
RX113 Group
Contents
Introduction ........................................................................................................................................ 3
The Basic of Capacitive Touch Switch .............................................................................................. 3
Generation of Electrostatic Capacity ................................................................................................................. 4
Capacitance-Current Conversion ...................................................................................................................... 5
Digitizing of Curr e nt ......................................................................................................................................... 7
ON/O F F swit ch judgment ................................................................................................................................. 7
The Capacitive Touch Detection System of Renesas ....................................................................... 9
Overview ........................................................................................................................................................... 9
Hardware ......................................................................................................................................................... 10
Overview ................................................................................................................................................ 10
I/O Driver & Drive pul s e generator ........................................................................................................ 11
Analog Fr ont End ................................................................................................................................... 11
3.2.4 Digital Control & CPU unit .................................................................................................................. 13
Firmware ......................................................................................................................................................... 15
Overview ................................................................................................................................................ 15
3.3.2 Physical Driver ............................................................................................................................................. 15
3.3.3 Middleware .................................................................................................................................................. 15
3.3.4 API ............................................................................................................................................................... 15
3.3.5 Application ................................................................................................................................................ 16
Designing a Touch Board and System............................................................................................ 16
Overview ......................................................................................................................................................... 16
Design of Cap touch board .............................................................................................................................. 16
Design of the self-capacitance method Cap touch key board ................................................................. 16
R01AN2516EU010
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RX113 Design Guide for Renesas Touc h Solution
Design of the mutual -capacita nce method Cap touch key board ............................................................ 20
CTSU register setting ...................................................................................................................................... 23
CTSU register setting for self-capacitance method ................................................................................ 23
CTS U regis t er set t ing for mutual-capacitance method ........................................................................... 29
Firmware process ............................................................................................................................................ 29
Firmware process of self-capacitance method ........................................................................................ 29
Noise Immunity ................................................................................................................................ 30
Overview ......................................................................................................................................................... 30
5.2 Noise Immunity on the Board ............................................................................................................................. 31
5.2.1 Pow e r Su pply Circuit ................................................................................................................................... 31
Touch Electrode and Wiring ................................................................................................................... 31
Software .......................................................................................................................................................... 32
Drift Correctio n Process ......................................................................................................................... 32
Countermeasure of Random Noise ......................................................................................................... 32
Debounce Filter ...................................................................................................................................... 33
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