AD7747 Datasheet, PDF (1/20 Pages) Analog Devices – 24-Bit Capacitance-to-Digital Converter with Temperature Sensor

Preliminary Technical Data
24-Bit Capacitance-to-Digital Converter
with Temperature Sensor
AD7747
FEATURES
GENERAL DESCRIPTION
Capacitance-to-digital converter
New standard in single chip solutions
Interfaces to single or differential grounded sensors
Resolution down to 40 aF (that is, up to 18.5-bit ENOB)
Accuracy: 8 fF
Linearity: 0.01%
Common-mode (not changing) capacitance up to 17 pF
Full scale (changing) capacitance range ±8 pF
Update rate: 5 Hz to 45 Hz
Simultaneous 50 Hz and 60 Hz rejection at 8.1 Hz update
Active shield for shielding sensor connection
The AD7747 is a high-resolution, Σ−∆ capacitance-to-digital
converter (CDC). The capacitance to be measured is connected
directly to the device inputs. The architecture features inherent
high resolution (24-bit no missing codes, up to 18 bit effective
resolution), high linearity (±0.01%), and high accuracy (±8 fF
factory calibrated). The AD7747 capacitance input range is
±8 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
1 mA current consumption
Operating temperature: –40°C to +125°C
16-lead TSSOP package
The AD7747 is designed for single ended or differential
capacitive sensors with one plate connected to ground.
For floating (not grounded) capacitive sensors, the AD7745 or
AD7746 are recommended.
The part has 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 part has a
standard voltage input, which together with the differential
reference input allows easy interface to an external temperature
APPLICATIONS
sensor, such as an RTD, thermistor, or diode.
Automotive, industrial, and medical systems for
The AD7747 has a 2-wire, I²C-compatible serial interface. The
Pressure measurement
part can operate with a single power supply 2.7 V to 5.25 V.
Position sensing
It is specified over the automotive temperature range of
Proximity sensing
Level sensing
–40°C to +125°C and are housed in a 16-lead TSSOP package.
Flowmeters
Impurity detection
FUNCTIONAL BLOCK DIAGRAMS
VDD
VIN(+)
VIN(-)
CIN1(+)
TEMP
SENSOR
MUX
CLOCK
GENERATOR
AD7747
24-BIT Σ-∆
MODULATOR
DIGITAL
FILTER
I2C
SERIAL
INTERFACE
SDA
SCL
CIN1(-)
SHLD
EXCITATION
CAP DAC 1
CAP DAC 2
CONTROL LOGIC
CALIBRATION
VOLTAGE
REFERENCE
RDY
REFIN(+) REFIN(-) GND
Figure 1.
Rev. PrC, 28. July 2006
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