Programmable Controller for Capacitance Touch Sensors

The AD7143 is an integrated capacitance-to-digital converter (CDC) with on-chip environmental calibration for use in systems requiring a novel user input method. The AD7143 interfaces to external capacitance sensors implementing functions, such as capacitive buttons, scroll bars, and scroll wheels.

The CDC has eight inputs channeled through a switch matrix to a 16-bit, 250 kHz sigma-delta (Σ-Δ) capacitance-to-digital converter. The CDC is capable of sensing changes in the capacitance of the external sensors and uses this information to register a sensor activation. The external sensors can be arranged as a series of buttons, as a scroll bar or wheel, or as a combination of sensor types. By programming the registers, the user has full control over the CDC setup. High resolution sensors require software to run on the host processor.

The AD7143 has on-chip calibration logic to account for changes in the ambient environment. The calibration sequence is performed automatically and at continuous intervals, while the sensors are not touched. This ensures that there are no false or non-registering touches on the external sensors due to a changing environment.

The AD7143 has an I2C-compatible serial interface and a separate VDRIVE pin for I2 serial interface operating voltages between 1.65 V and 3.6 V.

The AD7143 is available in a 16-lead, 4 mm x 4 mm LFCSP-VQ and operates from a 2.6 V to 3.6 V supply. The operating current consumption is less than 1 mA, falling to 50 μA in low power mode (conversion interval of 400 ms).

APPLICATIONS

* Personal music and multimedia players

* Cell phones

* Digital still cameras

* Smart hand-held devices

* Television, A/V, and remote controls

* Gaming consoles

* Programmable capacitance-to-digital converter

25 ms update rate (@ maximum sequence length)

Better than 1 fF resolution

8 capacitance sensor input channels

No external RC tuning components required

Automatic conversion sequencer

* On-chip automatic calibration logic

Automatic compensation for environmental changes

Automatic adaptive threshold and sensitivity levels