AD7148 Datasheet, PDF (1/56 Pages) Analog Devices – Programmable Touch Controller for Single Electrode Capacitance Sensors

Programmable Touch Controller for
Single Electrode Capacitance Sensors
AD7148
FEATURES
Programmable capacitance-to-digital converter (CDC)
Femtofarad (fF) resolution
8 capacitance sensor inputs
25 ms update rate, all 8 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 compatible with AD7143
On-chip RAM to store calibration data
I²C-compatible serial interface
Separate VDRIVE level for serial interface
Interrupt output
16-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
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 AD7148 is designed for use with capacitance sensors imple-
menting functions such as buttons, scroll bars, and wheels.
The sensors need only one PCB layer, enabling ultrathin
applications.
The AD7148 is an integrated capacitance-to-digital converter
(CDC) with on-chip environmental calibration. The CDC has
eight 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. 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 minimal software to run on the
host processor.
Rev. 0
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Trademarks and registered trademarks are the property of their respective owners.
CIN0 13
CIN1 14
CIN2 ₁₅
CIN3 ₁₆
CIN4 ₁
CIN5 2
CIN6 3
CIN7 4
FUNCTIONAL BLOCK DIAGRAM
AC_SHIELD V_CC
5
8
GND
7
BIAS
6
AD7148
EXCITATION
SOURCE
POWER-ON
RESET
LOGIC
CALIBRATION
RAM
16-BIT
Σ-Δ
CDC
CALIBRATION
ENGINE
CONTROL
AND
DATA
REGISTERS
SERIAL INTERFACE
AND CONTROL LOGIC
INTERRUPT
AND GPIO
LOGIC
9
10
11
12
V_DRIVE SDA
SCLK
INT
Figure 1.
The AD7148 is designed for single electrode capacitance sensors
(grounded sensors). There is an active shield output to minimize
noise pickup in the sensor. For floating, or two, electrode sensors,
use the AD7143.
The AD7148 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 AD7148 has an I²C®-compatible serial interface, as well as
an interrupt output. There is a VDRIVE pin to set the voltage level
for the serial interface independent of VCC.
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.
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