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PDF AD7745 Data sheet ( Hoja de datos )
| Número de pieza | AD7745 | |
| Descripción | (AD7745 / AD7746) 24-Bit Capacitance-to-Digital Converter | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD7745 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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24-Bit Capacitance-to-Digital Converter
with Temperature Sensor
AD7745/AD7746
FEATURES
GENERAL DESCRIPTION
Capacitance-to-digital converter
New standard in single chip solutions
Interfaces to single or differential floating sensors
Resolution down to 4 aF (that is, up to 21 ENOB)
Accuracy: 4 fF
Linearity: 0.01%
Common-mode (not changing) capacitance up to 17 pF
Full-scale (changing) capacitance range: ±4 pF
Tolerant of parasitic capacitance to ground up to 60 pF
Update rate: 10 Hz to 90 Hz
Simultaneous 50 Hz and 60 Hz rejection at 16 Hz
The AD7745/AD7746 are a high resolution, Σ-Δ capacitance-to-
digital converter (CDC). The capacitance to be measured is
connected directly to the device inputs. The architecture fea-
tures inherent high resolution (24-bit no missing codes, up to
21-bit effective resolution), high linearity (±0.01%), and high
accuracy (±4 fF factory calibrated). The AD7745/AD7746
capacitance input range is ±4 pF (changing), while it can accept
up to 17 pF common-mode capacitance (not changing), which
can be balanced by a programmable on-chip, digital-to-
capacitance converter (CAPDAC).
Temperature sensor on-chip
Resolution: 0.1°C, accuracy: ±2°C
Voltage input channel
Internal clock oscillator
2-wire serial interface (I2C®-compatible)
Power
2.7 V to 5.25 V single-supply operation
0.7 mA current consumption
Operating temperature: –40°C to +125°C
16-lead TSSOP package
The AD7745 has one capacitance input channel, while the
AD7746 has two channels. Each channel can be configured as
single-ended or differential. The AD7745/AD7746 are designed
for floating capacitive sensors. For capacitive sensors with one
plate connected to ground, the AD7747 is recommended.
The parts have an on-chip temperature sensor with a resolution
of 0.1°C and accuracy of ±2°C. The on-chip voltage reference
and the on-chip clock generator eliminate the need for any
external components in capacitive sensor applications. The
APPLICATIONS
parts have a standard voltage input, which together with the
differential reference input allows easy interface to an external
Automotive, industrial, and medical systems for
Pressure measurement
Position sensing
Level sensing
Flowmeters
Humidity sensing
Impurity detection
temperature sensor, such as an RTD, thermistor, or diode.
The AD7745/AD7746 have a 2-wire, I2C-compatible serial
interface. Both parts can operate with a single power supply
from 2.7 V to 5.25 V. They are specified over the automotive
temperature range of –40°C to +125°C and are housed in a
16-lead TSSOP package.
FUNCTIONAL BLOCK DIAGRAMS
VDD
VDD
VIN(+)
VIN(–)
CIN1(+)
CIN1(–)
TEMP
SENSOR
CLOCK
GENERATOR
AD7745
MUX
24-BIT Σ-∆
MODULATOR
DIGITAL
FILTER
I2C
SERIAL
INTERFACE
SDA
SCL
CAP DAC
CONTROL LOGIC
CALIBRATION
RDY
VIN(+)
VIN(–)
CIN1(+)
CIN1(–)
CIN2(+)
CIN2(–)
TEMP
SENSOR
CLOCK
GENERATOR
AD7746
MUX
24-BIT Σ-∆
MODULATOR
DIGITAL
FILTER
I2C
SERIAL
INTERFACE
SDA
SCL
CAP DAC
CONTROL LOGIC
CALIBRATION
RDY
EXCA
EXCB
CAP DAC
EXCITATION
VOLTAGE
REFERENCE
EXC1
EXC2
CAP DAC
EXCITATION
VOLTAGE
REFERENCE
REFIN(+) REFIN(–)
Figure 1.
GND
REFIN(+) REFIN(–)
Figure 2.
GND
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. Trademarks and
registered trademarks are the property of their respective owners.
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 © 2005 Analog Devices, Inc. All rights reserved.
1 page  
AD7745/AD7746
TIMING SPECIFICATIONS
VDD = 2.7 V to 3.6 V, or 4.75 V to 5.25 V; GND = 0 V; Input Logic 0 = 0 V; Input Logic 1 = VDD; –40°C to +125°C, unless otherwise noted.
Table 2.
Parameter
SERIAL INTERFACE1, 2
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
Set-Up Time (Start Condition), tSU;STA
Data Set-Up Time, tSU;DAT
Data Set-Up Time, tSU;DAT
Set-Up Time (Stop Condition), tSU;STO
Data Hold Time, tHD;DAT (Master)
Bus-Free Time (Between Stop and Start Condition, tBUF)
Min Typ Max
0 400
0.6
1.3
0.3
0.3
0.6
0.6
0.25
0.35
0.6
0
1.3
Unit
kHz
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
Test Conditions/Comments
See Figure 3
After this period, the first clock is generated
Relevant for repeated start condition
VDD ≥ 3.0 V
VDD < 3.0 V
1 Sample tested during initial release to ensure compliance.
2 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 3. Serial Interface Timing Diagram
P
Rev. 0| Page 5 of 28
5 Page 
AD7745/AD7746
OUTPUT NOISE AND RESOLUTION SPECIFICATIONS
The AD7745/AD7746 resolution is limited by noise. The noise
performance varies with the selected conversion time.
Table 5 shows typical noise performance and resolution for the
capacitive channel. These numbers were generated from 1000
Table 6 and Table 7 show typical noise performance and
resolution for the voltage channel. These numbers were
generated from 1000 data samples acquired in continuous
conversion mode with VIN pins shorted to ground.
data samples acquired in continuous conversion mode, at an
RMS noise represents the standard deviation and p-p noise
excitation of 32 kHz, ±VDD/2, and with all CIN and EXC pins
connected only to the evaluation board (no external capacitors.)
represents the difference between minimum and maximum
results in the data. Effective resolution is calculated from rms
noise, and p-p resolution is calculated from p-p noise.
Table 5. Typical Capacitive Input Noise and Resolution vs. Conversion Time
Conversion
Time (ms)
11.0
11.9
20.0
38.0
62.0
77.0
92.0
109.6
Output Data
Rate (Hz)
90.9
83.8
50.0
26.3
16.1
13.0
10.9
9.1
–3dB Frequency
(Hz)
87.2
79.0
43.6
21.8
13.8
10.5
8.9
8.0
RMS Noise
(aF/√Hz)
4.3
3.1
1.8
1.6
1.5
1.5
1.5
1.5
RMS
Noise (aF)
40.0
27.3
12.2
7.3
5.4
4.9
4.4
4.2
P-P
Noise (aF)
212.4
137.7
82.5
50.3
33.7
28.3
27.8
27.3
Effective Resolution
(Bits)
17.6
18.2
19.4
20.1
20.5
20.7
20.8
20.9
P-P Resolution
(Bits)
15.2
15.9
16.6
17.3
17.9
18.1
18.2
18.2
Table 6. Typical Voltage Input Noise and Resolution vs. Conversion Time, Internal Voltage Reference
Conversion
Time (ms)
20.1
32.1
62.1
122.1
Output Data
Rate (Hz)
49.8
31.2
16.1
8.2
–3dB Frequency
(Hz)
26.4
15.9
8.0
4.0
RMS Noise
(µV)
11.4
7.1
4.0
3.0
P-P Noise
(µV)
62
42
28
20
Effective Resolution
(Bits)
17.6
18.3
19.1
19.5
P-P Resolution
(Bits)
15.2
15.7
16.3
16.8
Table 7. Typical Voltage Input Noise and Resolution vs. Conversion Time, External 2.5 V Voltage Reference
Conversion
Time (ms)
20.1
32.1
62.1
122.1
Output Data
Rate (Hz)
49.8
31.2
16.1
8.2
–3dB Frequency
(Hz)
26.4
15.9
8.0
4.0
RMS Noise
(µV)
14.9
6.3
3.3
2.1
P-P Noise
(µV)
95
42
22
15
Effective Resolution
(Bits)
18.3
19.6
20.5
21.1
P-P Resolution
(Bits)
15.6
16.8
17.7
18.3
Rev. 0| Page 11 of 28
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet AD7745.PDF ] | |
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