Ultralow Power, 1.8 V, 3 mm 3 mm, 2-Channel Capacitance Converter AD7156 FEATURES GENERAL DESCRIPTION Ultralow power The AD7156 delivers a complete signal processing solution for Power supply voltage: 1.8 V to 3.6 V capacitive sensors, featuring an ultralow power converter with Operation power supply current: 70 A typical fast response time. Power-down current: 2 A typical The AD7156 uses an Analog Devices, Inc., capacitance-to- Fast response time digital converter (CDC) technology, which combines features Conversion time: 10 ms per channel important for interfacing to real sensors, such as high input Wake-up time from serial interface: 300 s sensitivity and high tolerance of both input parasitic ground Adaptive environmental compensation capacitance and leakage current. 2 capacitance input channels The integrated adaptive threshold algorithm compensates for Sensor capacitance (C ): 0 pF up to 13 pF SENS any variations in the sensor capacitance due to environmental Sensitivity up to 3 fF factors like humidity and temperature or due to changes in the 2 modes of operation dielectric material over time. Standalone with fixed settings Interfaced to a microcontroller for user-defined settings By default, the AD7156 operates in standalone mode using the 2 detection output flags fixed power-up settings and indicates detection on two digital 2 2-wire serial interface (I C-compatible) outputs. Alternatively, the AD7156 can be interfaced to a micro- Operating temperature: 40C to +85C controller via the serial interface, the internal registers can be 10-lead LFCSP package (3 mm 3 mm 0.8 mm) programmed with user-defined settings, and the data and status can be read from the part. APPLICATIONS The AD7156 operates with a 1.8 V to 3.6 V power supply. It is Buttons and switches specified over the temperature range of 40C to +85C. Proximity sensing Contactless switching Position detection Level detection Portable products FUNCTIONAL BLOCK DIAGRAM VDD CIN1 SCL C DIGITAL SERIAL SENS1 - CDC FILTER INTERFACE SDA EXC1 MUX AD7156 THRESHOLD OUT1 CIN2 C SENS2 EXCITATION EXC2 THRESHOLD OUT2 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 2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 07726-001AD7156 TABLE OF CONTENTS Features .............................................................................................. 1 Fixed Threshold Registers ......................................................... 18 Applications ....................................................................................... 1 Sensitivity Registers ................................................................... 18 General Description ......................................................................... 1 Timeout Registers ....................................................................... 18 Functional Block Diagram .............................................................. 1 Setup Registers ............................................................................ 19 Revision History ............................................................................... 2 Configuration Register .............................................................. 20 Specif icat ions ..................................................................................... 3 Power-Down Timer Register .................................................... 21 Timing Specifications .................................................................. 5 CAPDAC Registers .................................................................... 21 Absolute Maximum Ratings ............................................................ 6 Serial Number Register .............................................................. 21 ESD Caution .................................................................................. 6 Chip ID Register ......................................................................... 21 Pin Configuration and Function Descriptions ............................. 7 Serial Interface ................................................................................ 22 Typical Performance Characteristics ............................................. 8 Read Operation........................................................................... 22 Theory of Operation ...................................................................... 11 Write Operation.......................................................................... 22 Capacitance-to-Digital Converter ............................................ 11 AD7156 Reset ............................................................................. 23 CAPDAC ..................................................................................... 11 General Call ................................................................................ 23 Comparator and Threshold Modes .......................................... 12 Hardware Design Considerations ................................................ 24 Adaptive Threshold .................................................................... 12 Overview ..................................................................................... 24 Sensitivity..................................................................................... 12 Parasitic Capacitance to Ground .............................................. 24 Data Average ............................................................................... 13 Parasitic Resistance to Ground ................................................. 24 Hysteresis ..................................................................................... 13 Parasitic Parallel Resistance ...................................................... 24 Timeout ........................................................................................ 13 Parasitic Serial Resistance ......................................................... 25 Auto-DAC Adjustment .............................................................. 14 Input Overvoltage Protection ................................................... 25 Power-Down Timer ................................................................... 14 Input EMC Protection ............................................................... 25 Register Descriptions ..................................................................... 15 Power Supply Decoupling and Filtering .................................. 25 Status Register ............................................................................. 16 Application Examples ................................................................ 26 Data Registers ............................................................................. 17 Outline Dimensions ....................................................................... 27 Average Registers ........................................................................ 18 Ordering Guide .......................................................................... 27 REVISION HISTORY 10/08Revision 0: Initial Version Rev. 0 Page 2 of 28