Capacitive touch key driving principle and application scheme based on Atmel's AT42QT1110

The AT42QT1110 (QT1110) is a digital burst mode charge-transfer (QT™) capacitive sensor driver designed for any touch-key applications. The keys can be constructed in different shapes and sizes. Refer to the Touch Sensors Design Guide and Application Note QTAN0002, Secrets of a Successful QTouch™ Design, for

more

information on construction and design methods (both downloadable from the Atmel® website).

The device includes all signal processing functions necessary to provide stable sensing under a wide variety of changing conditions, and the outputs are fully debounced. Only a few external parts are required for operation.

The QT1110 modulates its bursts in a spread-spectrum fashion in order to suppress heavily the effects of external noise, and to suppress RF emissions.

AT42QT1110 Key Features:

• Sensor Keys:

– Up to 11 QTouch™ channels

• Data Acquisition:

– Measurement of keys triggered either by a signal applied to the SYNC pin or at
regular intervals timed by the AT42QT1110s internal clock

Keys measured sequentially for better performance, or in parallel clock groups for faster operation

– Raw data for key touches can be read as a report over the SPI interface

• Discrete Outputs:

– Configurable “Detect” outputs indicating individual key touch (7-key mode)

• Device Setup:

– Device configuration can be stored in EEPROM

• Technology:

– Patented spread-spectrum charge-transfer (direct mode)

• Key Outline Sizes:

– 6 mm x 6 mm or larger (panel thickness dependent); widely different sizes and
shapes possible, including solid or ring shapes

• Key Spacings:

– 7 mm center to center or more (panel thickness dependent)

• Layers Required:

– One

• Electrode Materials:

– Etched copper, silver, carbon, Indium Tin Oxide (ITO)

• Electrode Substrates:

– PCB, FPCB, plastic films, glass

• Panel Materials:

– Plastic, glass, composites, painted surfaces (low particle density metallic paints
possible)

• Panel Thickness:

– Up to 10 mm glass, 5 mm plastic (electrode size dependent)

• Key Sensit ivity:

– Individually settable via simple commands over serial interface

• Adjacent Key Suppression® (AKS™)

– Patented AKS technology to enable accurate key detection

• Interface:

– Full-duplex SPI slave mode (1.5 MHz), “change” pin, discrete detection outputs

• Moisture Tolerance Good

• Power:

– 3V ~ 5.5V

• Package:

– 32-pin 5 x 5 mm MLF RoHS compliant

– 32-pin 7 x 7 mm TQFP RoHS compliant

• Signal Processing:

– Self-calibration, auto drift compensation, noise filtering, AKS technology

AT42QT1110 Applications:

– Specific package qualified for automotive applications, such as radio, keyless
entry, electric windows and sat nav


Figure 1. AT42QT1110 7-key typical application with detection output and no external trigger


Figure 2. AT42QT1110 11-key typical application without external trigger

Figure 3. AT42QT1110 10-key typical application with external trigger (SYNC mode)