AD7148:  CapTouch™ Programmable Controller for Single-Electrode Capacitance Sensors

The AD7148 CapTouch™ Programmable 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 ultra thin applications.

The AD7148 is an integrated capacitance-to-digital converter (CDC) with on-chip environmental calibration. The CDC has 8 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. 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 minor software to run on the host processor.

The AD7148 is designed for single electrode capacitance sensors (grounded sensors.) There is an active shield output to minimize noise pick-up in the sensor. For floating, or two electrode sensors, use the AD7143.

The AD7148 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 active. This ensures that there are no false or non-registering touches on the external sensors due to a changing environment.

The AD7148 has an I²C-compatible serial interface, as well as interrupt output. There is a V_DRIVE pin to set the voltage level for the serial interface independently from V_CC.

The AD7148 is available in a 16-lead, 4 mm × 4 mm LFCSP and operates from a 2.6 V to 3.6 V supply. The operating current consumption in low power mode is typically 26 μA.

Applications

• Cell Phones
• Personal Music and Multimedia Players
• Smart Hand-held Devices
• Television, A/V and Remote Controls
• Gaming Consoles
• Digital Still Cameras