Renesas CTSU Application Note

Capacitive Sensor MCU
Capacitive Touch Noise Immunity Guide
Introduction
The Renesas Capacitive Touch Sensor Unit (CTSU) can be susceptible to noise in its surrounding
environment because it can detect minute changes in capacitance, generated by unwanted spurious
electrical signals (noise). The effect of this noise can depend on the hardware design. Therefore, taking
countermeasures at the design stage will lead to a CTSU MCU that is resilient to environmental noise and an
effective product development.
This application note describes ways to improve noise immunity for products using the Renesas Capacitive
Touch Sensor Unit (CTSU) in accordance with the IEC's noise immunity standards (IEC61000-4).
Target Device
RX Family, RA Family, RL78 Family MCUs and Renesas Synergy™ embedding the CTSU
(CTSU, CTSU2, CTSU2L, CTSU2La, CTSU2SL)
Standards covered in this application note
• IEC-61000-4-3
• IEC-61000-4-6
Contents
1. Overview .................................................................................................................................... 3
2. Noise Types and Countermeasures .......................................................................................... 4
2.1 EMC Standards ....................................................................................................................................... 4
2.2 RF Noise Countermeasures .................................................................................................................... 5
2.3 ESD Noise (electrostatic discharge) ....................................................................................................... 8
2.4 EFT Noise (Electrical Fast Transients) ................................................................................................... 8
3. CTSU Noise Countermeasure Functions .................................................................................. 9
3.1 Measurement Principles and Effect of Noise .......................................................................................... 9
3.2 CTSU1 ..................................................................................................................................................... 9
3.2.1 Random Phase Shift Function............................................................................................................... 9
3.2.2 High-frequency Noise Reduction Function (spread spectrum function) ............................................. 10
3.3 CTSU2 ................................................................................................................................................... 10
3.3.1 Multi-frequency Measurement ............................................................................................................. 10
3.3.2 Active Shield ........................................................................................................................................ 11
3.3.3 Non-measurement Channel Output Selection .................................................................................... 11
4. Hardware Noise Countermeasures ......................................................................................... 12
4.1 Typical Noise Countermeasures ........................................................................................................... 12
4.1.1 Touch Electrode Pattern Designs ....................................................................................................... 12
4.1.2 Power Supply Design .......................................................................................................................... 13
4.1.2.1 Voltage Supply Design ...................................................................................................................... 13
R30AN0426EJ0200 Rev.2.00
Dec.25.23
Application Note
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