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PDF AD7151 Data sheet ( Hoja de datos )
| Número de pieza | AD7151 | |
| Descripción | Capacitance Converter | |
| Fabricantes | Analog Devices | |
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Ultra-Low Power, 1-Channel, Capacitance
Converter for Proximity Sensing
AD7151
FEATURES
Ultra-low power
2.7 V to 3.6 V, 70 μA
Response time: 10 ms
Adaptive environmental compensation
1 capacitance input channel
Sensor capacitance (CSENS) 0 pF up to 13 pF
Sensitivity to 1 fF
EMC tested
2 modes of operation
Standalone with fixed settings
Interfaced to a microcontroller for user-defined settings
Proximity detection output flag
2-wire serial interface (I2C compatible)
Operating temperature
−40°C to +85°C
10-lead MSOP package
APPLICATIONS
Proximity sensing
Contactless switching
Position detection
Level detection
GENERAL DESCRIPTION
The AD7151 delivers a complete signal processing solution for
capacitive proximity sensors, featuring an ultra-low power
converter with fast response time. The AD7150 is a 2-channel
alternative to the AD7151.
The AD7151 uses Analog Devices, Inc., capacitance-to-digital
converter (CDC) technology, which combines features
important for interfacing to real sensors, such as high input
sensitivity and high tolerance of both input parasitic ground
capacitance and leakage current.
The integrated adaptive threshold algorithm compensates for
any variations in the sensor capacitance due to environmental
factors like humidity and temperature or due to changes in the
dielectric material over time.
By default, the AD7151 operates in standalone mode using the
fixed power-up settings and indicates detection on a digital
output. Alternatively, the AD7151 can be interfaced to a
microcontroller via the serial interface, the internal registers can
be programmed with user-defined settings, and the data and
status can be read from the part.
The AD7151 operates with a 2.7 V to 3.6 V power supply. It is
specified over the temperature range of −40°C to +85°C.
CSENS
FUNCTIONAL BLOCK DIAGRAM
VDD
CIN
Σ-Δ CDC
DIGITAL
FILTER
AD7151
SERIAL
INTERFACE
EXC
EXCITATION
THRESHOLD
SCL
SDA
OUT
GND
Figure 1.
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.
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  
AD7151
Parameter
Min Typ Max Unit1
POWER REQUIREMENTS
VDD-to-GND Voltage
2.7
3.6 V
IDD Current4
IDD Current Power-Down Mode4
70 80 μA
1 5 μA
3 10 μA
Test Conditions/Comments
VDD = 3.3 V, nominal
Temperature ≤ 25°C
Temperature = 85°C
1 Capacitance units: one picofarad (1 pF) = 1 × 10−12 farad (F); one femtofarad (1 fF) = 10−15 farad (F).
2 The CAPDAC can be used to shift (offset) the input range. The total capacitance of the sensor can, therefore, be up to the sum of the CAPDAC value and the conversion
input range. With the autoCAPDAC feature, the CAPDAC is adjusted automatically when the CDC input value is lower than 25% or higher than 75% of the CDC
nominal input range.
3 Specification is not production tested but is supported by characterization data at initial product release.
4 Digital inputs equal to VDD or GND.
TIMING SPECIFICATIONS
VDD = 2.7 V to 3.6 V; GND = 0 V; Input Logic 0 = 0 V; Input Logic 1 = VDD; –40°C to +85°C, unless otherwise noted.
Table 2.
Parameter
CONVERTER
Conversion Time
Wake-Up Time from Power-Down Mode1, 2
Power-Up Time1, 3
Reset Time1, 4
SERIAL INTERFACE5, 6
SCL Frequency
SCL High Pulse Width, tHIGH
SCL Low Pulse Width, tLOW
SCL, SDA Rise Time, tR
SCL, SDA Fall Time, tF
Hold Time (Start Condition), tHD;STA
Setup Time (Start Condition), tSU;STA
Data Setup Time, tSU;DAT
Setup Time (Stop Condition), tSU;STO
Data Hold Time (Master), tHD;DAT
Bus-Free Time (Between Stop and Start Condition), tBUF
Min Typ Max
10
0.3
2
2
0 400
0.6
1.3
0.3
0.3
0.6
0.6
0.1
0.6
10
1.3
Unit
ms
ms
ms
ms
kHz
μs
μs
μs
μs
μs
μs
μs
μs
ns
μs
Test Conditions/Comments
See Figure 2.
After this period, the first clock is generated.
Relevant for repeated start condition.
1 Specification is not production tested but is supported by characterization data at initial product release.
2 Wake-up time is the maximum delay between the last SCL edge writing the configuration register and the start of conversion.
3 Power-up time is the maximum delay between the VDD crossing the minimum level (2.7 V) and either the start of conversion or when ready to receive a serial interface
command.
4 Reset time is the maximum delay between the last SCL edge writing the reset command and either the start of conversion or when ready to receive a serial interface
command.
5 Sample tested during initial release to ensure compliance.
6 All input signals are specified with input rise/fall times = 3 ns, measured between the 10% and 90% points. Timing reference points at 50% for inputs and outputs.
Output load = 10 pF.
tLOW tR
tF
tHD;STA
SCL
tHD;STA
tHD;DAT
tHIGH
tSU;DAT
tSU;STA
tSU;STO
SDA
tBUF
PS
S
Figure 2. Serial Interface Timing Diagram
P
Rev. 0 | Page 4 of 28
5 Page 
AD7151
ARCHITECTURE AND MAIN FEATURES
3.3V
VDD
CLOCK
GENERATOR
POWER-DOWN
TIMER
POWER SUPPLY
MONITOR
SCL
CIN
Σ-Δ CDC
DIGITAL
FILTER
SERIAL
INTERFACE
PROGRAMMING
SDA INTERFACE
CX
EXC
CAPDAC
EXCITATION
THRESHOLD
AD7151
OUT
DIGITAL
OUTPUT
GND
Figure 20. AD7151 Block Diagram
The AD7151 core is a high performance capacitance-to-digital
converter (CDC) that allows the part to be interfaced directly to
a capacitive sensor.
The comparator compares the CDC result with thresholds, either
fixed or dynamically adjusted by the on-chip adaptive threshold
algorithm engine. Thus, the output indicates a defined change in
the input sensor capacitance.
The AD7151 also integrates an excitation source and CAPDAC
for the capacitive inputs, an input multiplexer, a complete clock
generator, a power-down timer, a power supply monitor, control
logic, and an I2C®-compatible serial interface for configuring the
part and accessing the internal CDC data and status, if required
in the system (see Figure 20).
CAPACITANCE-TO-DIGITAL CONVERTER
Figure 21 shows the CDC simplified functional diagram. The
converter consists of a second-order sigma delta (Σ-Δ), charge
balancing modulator and a third-order digital filter. The
measured capacitance CX is connected between an excitation
source and the Σ-Δ modulator input. The excitation signal is
applied on the CX during the conversion, and the modulator
continuously samples the charge going through the CX. The
digital filter processes the modulator output, which is a stream
of 0s and 1s containing the information in 0 and 1 density. The
data is processed by the adaptive threshold engine and output
comparators; the data can be also read through the serial interface.
The AD7151 is designed for floating capacitive sensors.
Therefore, both CX plates have to be isolated from ground or
any other fixed potential node in the system.
The AD7151 features slew rate limiting on the excitation voltage
output, which decreases the energy of higher harmonics on the
excitation signal and dramatically improves the system
electromagnetic compatibility (EMC).
CIN
CX
0pF TO 4pF
EXC
CAPACITANCE TO DIGITAL CONVERTER
(CDC)
CLOCK
GENERATOR
Σ-Δ
MODULATOR
0x000 TO 0xFFF
DATA
DIGITAL
FILTER
EXCITATION
Figure 21. CDC Simplified Block Diagram
CAPDAC
The AD7151 CDC core maximum full-scale input range is 4 pF.
However, the part can accept a higher capacitance on the input,
and the offset (nonchanging component) capacitance of up to 10
pF can be balanced by a programmable on-chip CAPDAC.
CIN
CSENS
10pF TO 14pF
EXC
CAPDAC
10pF
0x000 TO 0xFFF
DATA
0pF TO 4pF
CDC
Figure 22. Using CAPDAC
The CAPDAC can be understood as a negative capacitance
connected internally to the CIN pin. The CAPDAC has a 6-bit
resolution and a monotonic transfer function. Figure 22 shows
how to use the CAPDAC to shift the CDC 4 pF input range to
measure capacitance between 10 pF and 14 pF.
Rev. 0 | Page 10 of 28
11 Page | ||
| Páginas | Total 29 Páginas | |
| PDF Descargar | [ Datasheet AD7151.PDF ] | |
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