AD7747ARUZ Datasheet, PDF (1/28 Pages) Analog Devices – 24-Bit Capacitance-to-Digital Converter with Temperature Sensor

24-Bit Capacitance-to-Digital Converter
with Temperature Sensor
AD7747
FEATURES
Capacitance-to-digital converter
New standard in single chip solutions
Interfaces to single or differential grounded sensors
Resolution down to 20 aF (that is, up to 19.5-bit ENOB)
Accuracy: 10 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
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
APPLICATIONS
Automotive, industrial, and medical systems for
Pressure measurement
Position sensing
Proximity sensing
Level sensing
Flow metering
Impurity detection
GENERAL DESCRIPTION
The AD7747 is a high-resolution, Σ-Δ 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 19.5-bit effective
resolution), high linearity (±0.01%), and high accuracy (±10 fF
factory calibrated). The AD7747 capacitance input range is
±8 pF (changing), and it can accept up to 17 pF common-mode
capacitance (not changing), which can be balanced by a program-
mable on-chip digital-to-capacitance converter (CAPDAC).
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 that, together with the differential reference
input, allows easy interface to an external temperature sensor,
such as an RTD, thermistor, or diode.
The AD7747 has a 2-wire, I²C-compatible serial interface. The
part can operate with a single power supply of 2.7 V to 5.25 V.
It is specified over the automotive temperature range of
−40°C to +125°C and is housed in a 16-lead TSSOP package.
FUNCTIONAL BLOCK DIAGRAM
VDD
VIN(+)
TEMP
SENSOR
CLOCK
GENERATOR
AD7747
VIN(–)
CIN1(+)
CIN1(–)
MUX
24-BIT Σ-Δ
GENERATOR
DIGITAL
FILTER
I²C
SERIAL
INTERFACE
CONTROL LOGIC
CALIBRATION
SDA
SCL
RDY
SHLD
EXCITATION
CAP DAC 1
CAP DAC 2
VOLTAGE
REFERENCE
REFIN(+) REFIN(–)
GND
Figure 1.
Rev. 0
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