24-Bit Capacitance-to-Digital Converter with Temperature Sensor AD7747 FEATURES GENERAL DESCRIPTION Capacitance-to-digital converter The AD7747 is a high-resolution, - capacitance-to-digital New standard in single chip solutions converter (CDC). The capacitance to be measured is connected Interfaces to single or differential grounded sensors directly to the device inputs. The architecture features inherent Resolution down to 20 aF (that is, up to 19.5-bit ENOB) high resolution (24-bit no missing codes, up to 19.5-bit effective Accuracy: 10 fF resolution), high linearity (0.01%), and high accuracy (10 fF Linearity: 0.01% factory calibrated). The AD7747 capacitance input range is Common-mode (not changing) capacitance up to 17 pF 8 pF (changing), and it can accept up to 17 pF common-mode Full-scale (changing) capacitance range 8 pF capacitance (not changing), which can be balanced by a program- Update rate: 5 Hz to 45 Hz mable on-chip digital-to-capacitance converter (CAPDAC). Simultaneous 50 Hz and 60 Hz rejection at 8.1 Hz update The AD7747 is designed for single-ended or differential Active shield for shielding sensor connection capacitive sensors with one plate connected to ground. For Temperature sensor on-chip floating (not grounded) capacitive sensors, the AD7745 or Resolution: 0.1C, accuracy: 2C AD7746 are recommended. Voltage input channel The part has an on-chip temperature sensor with a resolution of Internal clock oscillator 2 0.1C and accuracy of 2C. The on-chip voltage reference and 2-wire serial interface (I C compatible) the on-chip clock generator eliminate the need for any external Power components in capacitive sensor applications. The part has a 2.7 V to 5.25 V single-supply operation standard voltage input that, together with the differential reference 0.7 mA current consumption input, allows easy interface to an external temperature sensor, Operating temperature: 40C to +125C such as an RTD, thermistor, or diode. 16-lead TSSOP package 2 The AD7747 has a 2-wire, I C-compatible serial interface. The APPLICATIONS part can operate with a single power supply of 2.7 V to 5.25 V. Automotive, industrial, and medical systems for It is specified over the automotive temperature range of Pressure measurement 40C to +125C and is housed in a 16-lead TSSOP package. Position sensing Proximity sensing Level sensing Flow metering Impurity detection FUNCTIONAL BLOCK DIAGRAM VDD TEMP SENSOR CLOCK AD7747 GENERATOR VIN(+) 2 VIN() SDA I C 24-BIT - DIGITAL MUX SERIAL GENERATOR FILTER INTERFACE SCL CIN1(+) CONTROL LOGIC RDY CIN1() CALIBRATION SHLD VOLTAGE CAP DAC 1 REFERENCE EXCITATION CAP DAC 2 REFIN(+) REFIN() 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 One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 05469-001AD7747 TABLE OF CONTENTS Features .............................................................................................. 1 Cap DAC A Register .................................................................. 19 Applications....................................................................................... 1 Cap DAC B Register................................................................... 19 General Description ......................................................................... 1 Cap Offset Calibration Register ............................................... 20 Functional Block Diagram .............................................................. 1 Cap Gain Calibration Register.................................................. 20 Revision History ............................................................................... 2 Volt Gain Calibration Register ................................................. 20 Specifications..................................................................................... 3 Circuit Description......................................................................... 21 Timing Specifications .................................................................. 5 Overview ..................................................................................... 21 Absolute Maximum Ratings............................................................ 6 Capacitance-to-Digital Converter............................................ 21 ESD Caution.................................................................................. 6 Active AC Shield Concept......................................................... 21 Pin Configuration and Function Descriptions............................. 7 CAPDAC ..................................................................................... 21 Typical Performance Characteristics ............................................. 8 Single-Ended Capacitive Configuration ................................. 22 Output Noise and Resolution Specifications .............................. 11 Differential Capacitive Configuration..................................... 22 Serial Interface ................................................................................ 12 Parasitic Capacitance ................................................................. 23 Read Operation........................................................................... 12 Parasitic Resistance .................................................................... 23 Write Operation.......................................................................... 12 Parasitic Serial Resistance ......................................................... 23 AD7747 Reset.............................................................................. 13 Capacitive Gain Calibration ..................................................... 23 General Call................................................................................. 13 Capacitive System Offset Calibration...................................... 24 Register Descriptions ..................................................................... 14 Internal Temperature Sensor .................................................... 24 Status Register............................................................................. 15 External Temperature Sensor ................................................... 24 Cap Data Register....................................................................... 15 Voltage Input............................................................................... 25 VT Data Register ........................................................................ 15 V Monitor ................................................................................ 25 DD Cap Setup Register ..................................................................... 16 Typical Application Diagram.................................................... 26 VT Setup Register....................................................................... 16 Outline Dimensions....................................................................... 27 EXC Setup Register .................................................................... 17 Ordering Guide .......................................................................... 27 Configuration Register .............................................................. 18 REVISION HISTORY 1/07Revision 0: Initial Version Rev. 0 Page 2 of 28