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PDF AD7148 Data sheet ( Hoja de datos )
| Número de pieza | AD7148 | |
| Descripción | Programmable Touch Controller | |
| Fabricantes | Analog Devices | |
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Programmable Touch Controller for
Single Electrode Capacitance Sensors
AD7148
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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
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.
CIN0 13
CIN1 14
CIN2 15
CIN3 16
CIN4 1
CIN5 2
CIN6 3
CIN7 4
FUNCTIONAL BLOCK DIAGRAM
ACSHIELD VCC
58
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
VDRIVE
10
SDA
11
SCLK
Figure 1.
12
INT
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.
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  
AD7148
I2C TIMING SPECIFICATIONS (AD7148-1)
TA = −40°C to +85°C, VDRIVE = 1.65 V to 3.6 V, 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.
www.daPtaarsahmeeet4teur.c1om
fSCLK
t1
t2
t3
t4
t5
t6
t7
t8
tR
tF
Limit
400
0.6
1.3
0.6
100
300
0.6
0.6
1.3
300
300
Unit
kHz max
μs min
μs min
μs min
ns min
ns min
μs min
μs min
μs min
ns max
ns max
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
1 Guaranteed by design, not production tested.
I2C Timing Diagram
SCLK
t2 tR
t1
t5
SDA
t8
STOP START
tF
t3
t4
t1
t7
START
Figure 2. I2C Detailed Timing Diagram
t6
STOP
Rev. 0 | Page 5 of 56
5 Page 
Registering a Sensor Activation
When a user approaches a sensor, the total capacitance associated
with that sensor changes and is measured by the AD7148. When
the capacitance changes to such an extent that a set threshold
is exceeded, the AD7148 registers this as a sensor activation.
www.datasheet4u.com
On-chip threshold limits are used to determine when sensor acti-
vation occurs. Figure 17 shows the change in CDC_RESULT_Sx
that occurs when a user activates a sensor. The sensor is deemed
to be active only when the value of CDC_RESULT_Sx is either
greater than the value of STAGEx_HIGH_THRESHOLD or less
than the value of STAGEx_LOW_THRESHOLD.
SENSOR ACTIVE (A)
CDC_RESULT_Sx
STAGEx_HIGH_THRESHOLD
AMBIENT OR
NO-TOUCH VALUE
STAGEx_LOW_THRESHOLD
SENSOR ACTIVE (B)
Figure 17. Sensor Activation Thresholds
In Figure 17, two different sensor activations are shown. Sensor
Activate (A) occurs when a sensor is connected to the positive
input of the converter. In this case, when a user activates the
sensor, there is an increase in the CDC code, and the value of
CDC_RESULT_Sx exceeds the value of STAGEx_HIGH_
THRESHOLD. Sensor Active (B) occurs when the sensor is
connected to the negative input of the converter. In this case, when
a user activates the sensor, there is a decrease in the CDC code,
and the value of CDC_RESULT_Sx becomes less than the value of
STAGEx_LOW_THRESHOLD.
For each conversion stage, the STAGEx_HIGH_THRESHOLD
and the STAGEx_LOW_THRESHOLD registers are in Register
Bank 3. The values in these registers are updated automatically
by the AD7148 due to its environmental calibration and adaptive
threshold logic.
At power-up, the values in the STAGEx_HIGH_THRESHOLD
and STAGEx_LOW_THRESHOLD registers are the same as those
in the STAGEx_OFFSET_HIGH and STAGEx_OFFSET_LOW
registers in Register Bank 2. The user must program the STAGEx_
OFFSET_HIGH and STAGEx_OFFSET_LOW registers on device
power-up. See the Environmental Calibration section for more
information.
Complete Solution for Capacitance Sensing
Analog Devices, Inc., provides a complete solution for capacitance
sensing. The two main elements of the solution are the sensor PCB
and the AD7148.
If the application requires high resolution sensors such as scroll
bars or wheels, software is required that runs on the host processor.
No position algorithm is required for button sensors.
AD7148
The memory requirements for the host depend on the sensor
and are typically 10 kB of code and 600 bytes of data memory,
depending on the sensor type.
SENSOR PCB
SPI OR I2C
AD7148
HOST PROCESSOR
1 MIPS
10kB ROM
600 BYTES RAM
Figure 18. Three-Part Capacitance Sensing Solution
Analog Devices supplies the sensor PCB footprint design libraries
to the customer and supplies any necessary software on an open-
source basis.
BIAS PIN
The BIAS pin (Pin 6) is connected internally to the bias node in
the AD7148. To ensure correct operation of the AD7148, connect
a 10 nF capacitor between the BIAS pin and ground. The voltage at
the BIAS pin is VCC/2.
OPERATING MODES
The AD7148 has three operating modes. Full power mode, in
which the device is always fully powered, is suited for applications
where power is not a concern (for example, game consoles that
have an ac power supply). Low power mode, in which the part
automatically powers down, is tailored to give significant power
savings over full power mode and is suited for mobile applications
where power must be conserved. In shutdown mode, the part
shuts down completely.
The POWER_MODE bits of the PWR_CONTROL register
(Address 0x000[1:0]) set the operating mode on the AD7148.
Table 7 shows the POWER_MODE settings for each operating
mode. To put the AD7148 into shutdown mode, set the
POWER_MODE bits to either 01 or 11.
Table 7. POWER_MODE Settings
POWER_MODE Bits
Operating Mode
00 Full power mode
01 Shutdown mode
10 Low power mode
11 Shutdown mode
The power-on default setting of the POWER_MODE bits is 00,
full power mode.
Full Power Mode
In full power mode, all sections of the AD7148 remain fully
powered and converting at all times. While a sensor is being
touched, the AD7148 processes the sensor data. If no sensor is
touched, the AD7148 measures the ambient capacitance level
and uses this data for the on-chip compensation routines. In full
power mode, the AD7148 converts at a constant rate. See the CDC
Conversion Sequence Time section for more information.
Rev. 0 | Page 11 of 56
11 Page | ||
| Páginas | Total 56 Páginas | |
| PDF Descargar | [ Datasheet AD7148.PDF ] | |
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