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CapTouch Programmable Controller for Single-Electrode Capacitance Sensors
AD7147A
SWITCH MATRIX
06663-001
FEATURES
Programmable capacitance-to-digital converter (CDC) Femtofarad (fF) resolution 13 capacitance sensor inputs 9 ms update rate, all 13 sensor inputs No external RC components required Automatic conversion sequencer
On-chip automatic calibration logic Automatic compensation for environmental changes Automatic adaptive threshold and sensitivity levels
Register map is compatible with the AD714x On-chip RAM to store calibration data Serial peripheral interface (SPI) (AD7147A) I2C-compatible serial interface (AD7147A-1) Separate VDRIVE level for serial interface Interrupt output and general-purpose input/output (GPIO) 25-ball, 2.3 mm × 2.1 mm WLCSP 2.6 V to 3.6 V supply voltage Low operating current
Full power mode: 1 mA Low power mode: 28.96 μA
APPLICATIONS
Cell phones Personal music and multimedia players Smart handheld devices Television, A/V, and remote controls Gaming consoles Digital still cameras
GENERAL DESCRIPTION
The AD7147A 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 AD7147A 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 and may require two PCB layers.
CIN0 D3 CIN1 A3 CIN2 B3 CIN3 A4 CIN4 C3 CIN5 A5 CIN6 B4 CIN7 B5 CIN8 C4 CIN9 C5 CIN10 D4 CIN11 D5 CIN12 E5
FUNCTIONAL BLOCK DIAGRAM
ACSHIELD VCC GND
E4 D2 E2
BIAS
E3
POWER-ON RESET LOGIC
EXCITATION SOURCE
AD7147A
CALIBRATION RAM
16-BIT Σ-Δ CDC
CALIBRATION ENGINE
CONTROL AND DATA REGISTERS
VDRIVE C2
SERIAL INTERFACE AND CONTROL LOGIC
INTERRUPT AND GPIO
LOGIC
B2 TP A2 GPIO
E1 D1 C1 B1
A1
SDO SDI SCLK CS
(SDA) (ADD0)
(ADD1)
INT
NOTES 1. PIN NAMES IN PARENTHESES ARE FOR THE AD7147A-1.
Figure 1.
The AD7147A is designed for single electrode capacitance sensors (grounded sensors). There is an active shield output to minimize noise pickup in the sensor.
The AD7147A 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 AD7147A has an SPI-compatible serial interface, and the AD7147A-1 has an I2C®-compatible serial interface. Both parts have an interrupt output, as well as a GPIO. There is a VDRIVE pin to set the voltage level for the seri.