3 V/5 V, 1 mW, 2-/3-Channel, 16-Bit, Sigma-Delta ADCs AD7705/AD7706 FEATURES FUNCTIONAL BLOCK DIAGRAM V AD7705: 2 fully differential input channel ADCs DD REF IN() REF IN(+) AD7706: 3 pseudo differential input channel ADCs AD7705/AD7706 16 bits no missing codes CHARGE BALANCING 0.003% nonlinearity A/D CONVERTER Programmable gain front end: gains from 1 to 128 ANALOG - PGA INPUT MAX BUFFER MODULATOR 3-wire serial interface CHANNELS SPI-, QSPI-, MICROWIRE-, and DSP-compatible A = 1 128 Schmitt-trigger input on SCLK DIGITAL FILTER Ability to buffer the analog input 2.7 V to 3.3 V or 4.75 V to 5.25 V operation Power dissipation 1 mW maximum 3 V SERIAL INTERFACE Standby current 8 A maximum REGISTER BANK 16-lead PDIP, 16-lead SOIC, and 16-lead TSSOP packages MCLK IN SCLK CLOCK GENERATION MCLK OUT CS GENERAL DESCRIPTION DIN The AD7705/AD7706 are complete analog front ends for low DOUT frequency measurement applications. These 2-/3-channel devices can accept low level input signals directly from a transducer and GND DRDY RESET produce serial digital output. The devices employ a - Figure 1. conversion technique to realize up to 16 bits of no missing codes performance. The selected input signal is applied to a The AD7705/AD7706 devices, with a 3 V supply and a 1.225 V proprietary, programmable-gain front end based around an reference, can handle unipolar input signal ranges of 0 mV to analog modulator. The modulator output is processed by an on- 10 mV through 0 V to 1.225 V. The devices can accept bipolar chip digital filter. The first notch of this digital filter can be pro- input ranges of 10 mV through 1.225 V. Therefore, the grammed via an on-chip control register, allowing adjustment of AD7705/AD7706 devices perform all signal conditioning and the filter cutoff and output update rate. conversion for a 2-channel or 3-channel system. The AD7705/AD7706 devices operate from a single 2.7 V to The AD7705/AD7706 are ideal for use in smart, microcontroller, 3.3 V or 4.75 V to 5.25 V supply. The AD7705 features two fully or DSP-based systems. The devices feature a serial interface that differential analog input channels the AD7706 features three can be configured for 3-wire operation. Gain settings, signal pseudo differential input channels. polarity, and update rate selection can be configured in software using the input serial port. The parts contains self-calibration and Both devices feature a differential reference input. Input signal system calibration options to eliminate gain and offset errors on ranges of 0 mV to 20 mV through 0 V to 2.5 V can be the part itself or in the system. CMOS construction ensures very incorporated on both devices when operating with a V of 5 V DD low power dissipation, and the power-down mode reduces the and a reference of 2.5 V. They can also handle bipolar input standby power consumption to 20 W typ. signal ranges of 20 mV through 2.5 V, which are referenced to the AIN() inputs on the AD7705 and to the COMMON input These parts are available in a 16-lead, wide body (0.3 inch), on the AD7706. plastic dual in-line package (DIP) a 16-lead, wide body (0.3 inch), standard small outline (SOIC) package and a low profile, 16-lead, thin shrink small outline package (TSSOP). Rev. C 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 2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 01166-001AD7705/AD7706 TABLE OF CONTENTS Features .............................................................................................. 1 Reference Input........................................................................... 23 General Description ......................................................................... 1 Digital Filtering........................................................................... 23 Functional Block Diagram .............................................................. 1 Analog Filtering.......................................................................... 25 Revision History ............................................................................... 3 Calibration................................................................................... 25 Product Highlights ........................................................................... 4 Theory of Operation ...................................................................... 28 Specifications..................................................................................... 5 Clocking and Oscillator Circuit ............................................... 28 Timing Characteristics ................................................................ 8 System Synchronization ............................................................ 28 Absolute Maximum Ratings............................................................ 9 RESET Input ............................................................................... 29 ESD Caution.................................................................................. 9 Standby Mode ............................................................................. 29 Pin Configurations and Function Descriptions ......................... 10 Accuracy...................................................................................... 29 Output Noise (5 V Operation)...................................................... 12 Drift Considerations .................................................................. 29 Output Noise (3 V Operation)...................................................... 13 Power Supplies............................................................................ 30 Typical Performance Characteristics ........................................... 14 Supply Current............................................................................ 30 On-Chip Registers.......................................................................... 16 Grounding and Layout .............................................................. 30 Communication Register (RS2, RS1, RS0 = 0, 0, 0)............... 16 Evaluating the Performance...................................................... 31 Setup Register (RS2, RS1, RS0 = 0, 0, 1) Power-On/Reset Digital Interface.......................................................................... 31 Status: 01 Hexadecimal.............................................................. 17 Configuring the AD7705/AD7706 .......................................... 33 Clock Register (RS2, RS1, RS0 = 0, 1, 0) Power-On/Reset Microcomputer/Microprocessor Interfacing ......................... 34 Status: 05 Hexadecimal.............................................................. 19 Code For Setting Up the AD7705/AD7706............................ 35 Data Register (RS2, RS1, RS0 = 0, 1, 1) ................................... 20 Applications..................................................................................... 38 Test Register (RS2, RS1, RS0 = 1, 0, 0) Power-On/Reset Status: 00 Hexadecimal.............................................................. 20 Pressure Measurement............................................................... 38 Zero-Scale Calibration Register (RS2, RS1, RS0 = 1, 1, 0) Temperature Measurement ....................................................... 39 Power-On/Reset Status: 1F4000 Hexadecimal........................... 20 Smart Transmitters..................................................................... 40 Full-Scale Calibration Register (RS2, RS1, RS0 = 1, 1, 1) Power-On/Reset Status: 5761AB HexaDecimal......................... 20 Battery Monitoring .................................................................... 41 Circuit Description......................................................................... 21 Outline Dimensions....................................................................... 42 Analog Input ............................................................................... 22 Ordering Guide .......................................................................... 43 Bipolar/Unipolar Input.............................................................. 22 Rev. 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