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CapTouch™ Programmable Controller for Single-Electrode Capacitance Sensors
AD7147
FEATURES www.datasheet4u.com
Programmable capacitance-to-digital converter (CDC) Femtofarad 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 AD7142 On-chip RAM to store calibration data SPI-compatible (serial-peripheral-interface-compatible) serial interface (AD7147) I2C-compatible serial interface (AD7147-1) Separate VDRIVE level for serial interface Interrupt output and general-purpose input/output (GPIO) 24-lead, 4 mm × 4 mm LFCSP 2.6 V to 3.3 V supply voltage Low operating current Full power mode: 1 mA Low power mode: 21.5 μA
FUNCTIONAL BLOCK DIAGRAM
ACSHIELD VCC
8 11
GND
10
BIAS
9
CIN0 19 CIN1 20 CIN2 21 CIN3 22 CIN4 23 EXCITATION SOURCE
POWER-ON RESET LOGIC
CIN6 1 CIN7 2 CIN8 3 CIN9 4 CIN10 5 CIN11 6 CIN12 7
SWITCH MATRIX
CIN5 24
AD7147
CALIBRATION RAM
16-BIT Σ-Δ CDC
CALIBRATION ENGINE
CONTROL AND DATA REGISTERS
VDRIVE 12
SERIAL INTERFACE AND CONTROL LOGIC
INTERRUPT AND GPIO LOGIC
18 GPIO
APPLICATIONS
Cell phones Personal music and multimedia players Smart handheld devices Television, A/V, and remote controls Gaming consoles Digital still cameras
SDO/ SDI/ SCLK CS/ SDA ADD0 ADD1
INT
Figure 1. AD7147 Block Diagram
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 VDRIVE pin to set the voltage level for the serial interface independent of VCC. 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 consumption in low power mode is typically 26 μA for 13 sensors.
GENERAL DESCRIPTION
The AD7147 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 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 (∑-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.
Rev. 0
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AD7147 TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1
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Capacitance Sensor Behavior Without Calibration............... 23 Capacitance Sensor Behavior with Calibration...................... 24 Slow FIFO.................................................................................... 24 SLOW_FILTER_UPDATE_LVL .............................................. 24 Adaptive Threshold and Sensitivity ............................................. 25 Interrupt Output............................................................................. 27 CDC Conversion-Complete Interrupt .................................... 27 Sensor-Touch Interrupt ............................................................. 27 GPIO INT Output Control ....................................................... 29 Outputs ............................................................................................ 31 ACSHIELD Output .......................................................................... 3.