CapTouch™ Programmable Controller for
Single-Electrode Capacitance Sensors
AD7147
FUNCTIONAL BLOCK DIAGRAM
FEATURES
AC
V
GND
10
BIAS
9
SHIELD
CC
Programmable capacitance-to-digital converter (CDC)
Femtofarad resolution
8
11
POWER-ON
RESET LOGIC
13 capacitance sensor inputs
19
20
21
22
23
24
1
CIN0
CIN1
CIN2
CIN3
CIN4
CIN5
CIN6
CIN7
CIN8
CIN9
CIN10
CIN11
CIN12
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
EXCITATION
SOURCE
CALIBRATION
AD7147
RAM
2
3
16-BIT
Σ-Δ
CDC
CALIBRATION
ENGINE
4
5
6
CONTROL
AND DATA
REGISTERS
7
2.6 V to 3.3 V supply voltage
INTERRUPT
AND GPIO
LOGIC
Low operating current
Full power mode: 1 mA
SERIAL INTERFACE
AND CONTROL LOGIC
12
18
GPIO
V
DRIVE
Low power mode: 21.5 μA
13
14
15
16
17
SDO/ SDI/ SCLK CS/
SDA ADD0 ADD1
INT
APPLICATIONS
Cell phones
Figure 1. AD7147 Block Diagram
Personal music and multimedia players
Smart handheld devices
Television, A/V, and remote controls
Gaming consoles
The AD7147 is designed for single-electrode capacitance
sensors (grounded sensors). There is an active shield output to
minimize noise pickup in the sensor.
Digital still cameras
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.
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.
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 con-
sumption in low power mode is typically 26 μA for 13 sensors.
High resolution sensors require minor software to run on the
host processor.
Rev. 0
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