AD7147:  CapTouch™ Programmable Controller for Single-Electrode Capacitance Sensors

The AD7147 CapTouch™ controller is designed for use with capacitance sensors implementing functions such as buttons, scroll bars, and wheels. The sensors need only one PCB layer, enabling ultrathin applications.

The AD7147 is an integrated CDC with on-chip environmental calibration. The CDC has 13 inputs channeled through a switch matrix to a 16-bit, 250 kHz sigma-delta (Σ-Δ) converter. The CDC is capable of sensing changes in the capacitance of the external sensors and uses this information to register a sensor activation. By programming the registers, the user has full control over the CDC setup.

High resolution sensors require minor software to run on the host processor.

The AD7147 is designed for single electrode capacitance sensors (grounded sensors). There is an active shield output to minimize noise pickup in the sensor.

The AD7147 has on-chip calibration logic to compensate for changes in the ambient environment. The calibration sequence is performed automatically and at continuous intervals as long as the sensors are not touched. This ensures that there are no false or nonregistering touches on the external sensors due to a changing environment.

The AD7147 has an SPI-compatible serial interface, and the AD7147-1 has an I²C®-compatible serial interface. Both parts have an interrupt output, as well as a GPIO. There is a V_DRIVE pin to set the voltage level for the serial interface independent of V_CC.

The AD7147 is available in a 24-lead, 4 mm × 4 mm LFCSP and operates from a 2.6 V to 3.6 V supply. The operating current con-sumption in low power mode is typically 26 μA for 13 sensors.

Applications

• Cell phones
• Personal music and multimedia players
• Smart handheld devices
• Television, A/V, and remote controls
• Gaming consoles
• Digital still cameras