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PDF AD7143 Data sheet ( Hoja de datos )
| Número de pieza | AD7143 | |
| Descripción | integrated capacitance-to-digital converter | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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FEATURES
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
2.6 V to 3.6 V supply voltage
Low operating current
Full power mode: less than 1 mA
Low power mode: 50 μA
APPLICATIONS
Personal music and multimedia players
Cell phones
Digital still cameras
Smart hand-held devices
Television, A/V, and remote controls
Gaming consoles
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 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.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
Programmable Controller for
Capacitance Touch Sensors
AD7143
FUNCTIONAL BLOCK DIAGRAM
CIN0 15
CIN1 16
CIN2 1
CIN3 2
CIN4 3
CIN5 4
CIN6 5
CIN7 6
AD7143
POWER-ON
RESET
LOGIC
16-BIT
Σ-Δ
CDC
CALIBRA-
TION
ENGINE
CONTROL
AND
DATA
REGISTERS
CALIBRA-
TION
RAM
9 VCC
10 GND
CSHIELD 7
SRC 8
250kHz
EXCITATION
SOURCE
I2C SERIAL INTERFACE
AND CONTROL LOGIC
INTERRUPT
LOGIC
11 12 13
VDRIVE SDA SCLK
14
INT
Figure 1.
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.
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 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).
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2007 Analog Devices, Inc. All rights reserved.
1 page  
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AD7143
I2C TIMING SPECIFICATIONS
TA = −40°C to +85°C, VCC = 2.6 V to 3.6 V, unless otherwise noted. Sample tested at 25°C to ensure compliance. All input signals timed
from a voltage level of 1.6 V.
Table 4. I2C Timing Specifications1
Parameter
Limit
Unit
fSCLK 400 kHz max
t1 0.6 μs min
t2 1.3 μs min
t3 0.6 μs min
t4 100 ns min
t5 300 ns min
t6 0.6 μs min
t7 0.6 μs min
t8 1.3 μs min
tR 300 ns max
tF 300 ns max
1 Guaranteed by design, not production tested.
Description
Start condition hold time, tHD; STA
Clock low period, tLOW
Clock high period, tHIGH
Data setup time, tSU; DAT
Data hold time, tHD; DAT
Stop condition setup time, tSU; STO
Start condition setup time, tSU; STA
Bus free time between stop and start conditions, tBUF
Clock/data rise time
Clock/data fall time
200µA
IOL
TO OUTPUT
PIN CL
50pF
1.6V
200µA
IOH
Figure 2. Load Circuit for Digital Output Timing Specifications
Rev. 0 | Page 5 of 56
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THEORY OF OPERATION
The AD7143 is a capacitance-to-digital converter (CDC) with
on-chip environmental compensation, intended for use in
portable systems requiring high resolution user input. The
internal circuitry consists of a 16-bit, ∑-Δ converter that
converts a capacitive input signal into a digital value. There are
eight input pins, CIN0 to CIN7, on the AD7143. A switch
matrix routes the input signals to the CDC. The result of each
capacitance-to-digital conversion is stored in on-chip registers.
The host subsequently reads the results over the serial interface.
The AD7143 has an I2C interface, ensuring that the parts are
compatible with a wide range of host processors.
The AD7143 interfaces with up to eight external capacitance
sensors. These sensors can be arranged as buttons, scroll bars,
wheels, or as a combination of sensor types. The external
sensors consist of electrodes on a single or multiple layer PCB
that interface directly to the AD7143.
The AD7143 can be set up to implement any set of input
sensors by programming the on-chip registers. The registers can
also be programmed to control features such as averaging,
offsets, and gains for each of the external sensors. There is a
sequencer on-chip to control how each of the capacitance
inputs is polled.
The AD7143 has on-chip digital logic and 528 words of RAM
used for environmental compensation. The effects of humidity,
temperature, and other environmental factors can effect the
operation of capacitance sensors. Transparent to the user, the
AD7143 performs continuous calibration to compensate for
these effects, allowing the AD7143 to give error-free results at
all times.
The AD7143 requires some minor companion software that
runs on the host or other microcontroller to implement high
resolution sensor functions, such as a scroll bar or wheel.
However, no host software is required to implement buttons,
including 8-way button functionality. Button sensors are
implemented completely in digital logic on-chip with the status
of each button reported in interrupt status registers.
The AD7143 can be programmed to operate in either full power
mode, or in low power automatic wake-up mode. The
automatic wake-up mode is particularly suited for portable
devices that require low power operation giving the user
significant power savings coupled with full functionality.
The AD7143 has an interrupt output, INT, to indicate when
new data has been placed into the registers. INT is used to
interrupt the host on sensor activation.
AD7143
The AD7143 operates from a 2.6 V to 3.6 V supply, and is
available in a 16-lead, 4 mm × 4 mm LFCSP_VQ.
CAPACITANCE SENSING THEORY
The AD7143 uses a method of sensing capacitance known as
the shunt method. Using this method, an excitation source is
connected to a transmitter generating an electric field to a
receiver. The field lines measured at the receiver are translated
into the digital domain by a ∑-Δ converter. When a finger, or
other grounded object, interferes with the electric field, some of
the field lines are shunted to ground and do not reach the
receiver (see Figure 17). Therefore, the total capacitance
measured at the receiver decreases when an object comes close
to the induced field.
PLASTIC COVER
Rx
PCB LAYER
Tx
Σ-Δ
ADC
AD7143
16-BIT
DATA
EXCITATION
SIGNAL
250kHz
Figure 17. Single Layer Sensing Capacitance Method
In practice, the excitation source and ∑-Δ ADC are implemented
on the AD7143, while the transmitter and receiver are constructed
on a PCB that comprises the external sensor.
Registering a Sensor Activation
When a sensor is approached, the total capacitance associated
with that sensor, measured by the AD7143, changes. When the
capacitance changes to such an extent that a set threshold is
exceeded, the AD7143 registers this as a sensor touch and then
automatically updates the internal interrupt status registers.
Preprogrammed threshold levels are used to determine if a
change in capacitance is due to a button being activated. If the
capacitance exceeds one of the threshold limits, the AD7143
registers this as a true button activation. The same threshold
principle is used to determine if other types of sensors, such as
sliders or scroll wheels, are activated.
Rev. 0 | Page 11 of 56
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet AD7143.PDF ] | |
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