24-Bit Capacitance-to-Digital Converter
with Temperature Sensor
AD7747
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 ©2007 Analog Devices, Inc. All rights reserved.
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 (I
2
C® 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- 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, I
2
C-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
VIN(+)
DD
CIN1(+)
VIN(–)
SHLD
GND
SDA
SCL
RDY
CIN1(–)
REFIN(+) REFIN(–)
TEMP
SENSOR
24-BIT Σ-Δ
GENERATOR
DIGITAL
FILTER
I
2
C
SERIAL
INTERFACE
EXCITATION
CONTROL LOGIC
CALIBRATION
VOLTAGE
REFERENCE
CAP DAC 1
CAP DAC 2
CLOCK
GENERATOR
MUX
AD7747
05469-001
Figure 1.
