Programmable Controller for
Capacitance Touch Sensors
AD7143
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Programmable capacitance-to-digital converter
25 ms update rate (@ maximum sequence length)
Better than 1 fF resolution
8 capacitance sensor input channels
No external RC tuning components required
Automatic conversion sequencer
On-chip automatic calibration logic
Automatic compensation for environmental changes
Automatic adaptive threshold and sensitivity levels
On-chip RAM to store calibration data
I2C®-compatible serial interface
Separate VDRIVE level for serial interface
Interrupt output for host controller
16-lead, 4 mm x 4 mm LFCSP-VQ
POWER-ON
RESET
AD7143
15
16
1
CIN0
CIN1
CIN2
CIN3
CIN4
CIN5
CIN6
CIN7
LOGIC
CALIBRA-
TION
ENGINE
16-BIT
Σ-Δ
CDC
2
3
4
5
CALIBRA-
TION
9
VCC
GND
6
CONTROL
AND
RAM
10
DATA
REGISTERS
250kHz
7
8
CSHIELD
SRC
EXCITATION
SOURCE
INTERRUPT
LOGIC
2
I C SERIAL INTERFACE
AND CONTROL LOGIC
2.6 V to 3.6 V supply voltage
Low operating current
11
12
13
14
Full power mode: less than 1 mA
VDRIVE SDA SCLK
INT
Low power mode: 50 μA
Figure 1.
APPLICATIONS
Personal music and multimedia players
Cell phones
Digital still cameras
Smart hand-held devices
Television, A/V, and remote controls
Gaming consoles
The AD7143 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 touched. This ensures that there are no false or
nonregistering touches on the external sensors due to a
changing environment.
GENERAL DESCRIPTION
The AD7143 is an integrated capacitance-to-digital converter
(CDC) with on-chip environmental calibration for use in
systems requiring a novel user input method. The AD7143
interfaces to external capacitance sensors implementing
functions, such as capacitive buttons, scroll bars, and
scroll wheels.
The AD7143 has an I2C-compatible serial interface and a
separate VDRIVE pin for I2C serial interface operating voltages
between 1.65 V and 3.6 V.
The CDC has eight inputs channeled through a switch matrix to
a 16-bit, 250 kHz sigma-delta (∑-Δ) capacitance-to-digital
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 software to run on the host processor.
The AD7143 is available in a 16-lead, 4 mm × 4 mm LFCSP-VQ
and operates from a 2.6 V to 3.6 V supply. The operating
current consumption is less than 1 mA, falling to 50 μA in low
power mode (conversion interval of 400 ms).
Rev. 0
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