3 V/5 V, 10 V Input Range, 1 mW 3-Channel 16-Bit, Sigma-Delta ADC AD7707 FEATURES FUNCTIONAL BLOCK DIAGRAM DV AV DD DD REF IN() REF IN(+) Charge balancing ADC AD7707 16 bits, no missing codes 0.003% nonlinearity CHARGE BALANCING High level (10 V) and low level (10 mV) input channels A/D CONVERTER AIN1 True bipolar 100 mV capability on low level input AIN2 - BUF PGA MUX MODULATOR LOCOM Channels without requiring charge pumps 30k A = 1 128 Programmable gain front end AIN3 DIGITAL FILTER 5k Gains from 1 to 128 VBIAS 5k 3-wire serial interface SPI, QSPI, MICROWIRE and DSP compatible 15k HICOM Schmitt trigger input on SCLK SERIAL INTERFACE 30k Ability to buffer the analog input REGISTER BANK SCLK 2.7 V to 3.3 V or 4.75 V to 5.25 V operation CS Power dissipation 1 mW at 3 V MCLK IN DIN CLOCK Standby current 8 A maximum GENERATION MCLK OUT DOUT 20-lead SOIC and TSSOP packages GENERAL DESCRIPTION AGND DGND DRDY RESET Figure 1. The AD7707 is a complete analog front end for low frequency measurement applications. This 3-channel device can accept for 3-wire operation. Gain settings, signal polarity and update either low level input signals directly from a transducer or high rate selection can be configured in software using the input level (10 V) signals and produce a serial digital output. It employs serial port. The part contains self-calibration and system calibra- a - conversion technique to realize up to 16 bits of no missing tion options to eliminate gain and offset errors on the part itself codes performance. The selected input signal is applied to a or in the system. proprietary programmable gain front end based around an analog CMOS construction ensures very low power dissipation, and the modulator. The modulator output is processed by an on-chip power-down mode reduces the standby power consumption to digital filter. The first notch of this digital filter can be pro- 20 W typical. This part is available in a 20-lead wide body (0.3 grammed via an on-chip control register allowing adjustment inch) small outline (SOIC) package and a low profile 20-lead TSSOP. of the filter cutoff and output update rate. PRODUCT HIGHLIGHTS The AD7707 operates from a single 2.7 V to 3.3 V or 4.75 V to 5.25 V supply. The AD7707 features two low level pseudo differen- 1. The AD7707 consumes less than 1 mW at 3 V supplies and tial analog input channels, one high level input channel and a 1 MHz master clock, making it ideal for use in low power differential reference input. Input signal ranges of 0 mV to 20 mV systems. Standby current is less than 8 A. through 0 V to 2.5 V can be accommodated on both low level input 2. On-chip thin-film resistors allow 10 V, 5 V, 0 V to 10 V, channels when operating with a VDD of 5 V and a reference of and 0 V to 5 V high level input signals to be directly accom- 2.5 V. They can also handle bipolar input signal ranges of 20 mV modated on the analog inputs without requiring split supplies through 2.5 V, which are referenced to the LCOM input. The or charge-pumps. AD7707, with a 3 V supply and a 1.225 V reference, can handle 3. The low level input channels allow the AD7707 to accept unipolar input signal ranges of 0 mV to 10 mV through 0 V to input signals directly from a strain gage or transducer 1.225 V. Its bipolar input signal ranges are 10 mV through 1.225 V. removing a considerable amount of signal conditioning. 4. The part features excellent static performance specifications The high level input channel can accept input signal ranges of 10 V, with 16 bits, no missing codes, 0.003% accuracy, and low 5 V, 0 V to 10 V and 0 V to 5 V. The AD7707 thus performs all rms noise. Endpoint errors and the effects of temperature signal conditioning and conversion for a 3-channel system. drift are eliminated by on-chip calibration options, which The AD7707 is ideal for use in smart, microcontroller or DSP- remove zero-scale and full-scale errors. based systems. It features a serial interface that can be configured Rev. B 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 20002010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 08691-001AD7707 TABLE OF CONTENTS Features .............................................................................................. 1 Span and Offset Limits on the Low Level Input Channels, AIN1 and AIN2 .......................................................................... 31 General Description ......................................................................... 1 Span and Offset Limits on the High Level Input Channel Functional Block Diagram .............................................................. 1 AIN3 ............................................................................................. 31 Product Highlights ........................................................................... 1 Power-Up and Calibration ........................................................ 32 Revision History ............................................................................... 3 Using the AD7707 .......................................................................... 33 Specif icat ions ..................................................................................... 4 Clocking and Oscillator Circuit ............................................... 33 Timing Characteristics ................................................................ 8 System Synchronization ............................................................ 33 Absolute Maximum Ratings ............................................................ 9 Reset Input .................................................................................. 34 ESD Caution .................................................................................. 9 Standby Mode ............................................................................. 34 Pin Configuration and Function Descriptions ........................... 10 Accuracy ...................................................................................... 34 Typical Performance Characteristics ........................................... 12 Drift Considerations .................................................................. 34 OV tput Noise .................................................................................. 14 Power Supplies ................................................................................ 35 Output Noise For Low Level Input Channels Supply Current ............................................................................ 35 (5 V Operation) .......................................................................... 14 Grounding and Layout .............................................................. 35 Output Noise For Low Level Input Channels (3 V Operation) .......................................................................... 15 Digital Interface .............................................................................. 36 Output Noise For High Level Input Channel AIN3 Configuring the AD7707 ............................................................... 37 (5 V Operation) .......................................................................... 16 Microcomputer/Microprocessor Interfacing .............................. 39 Output Noise For High Level Input Channel AIN3 AD7707 to 68HC11 Interface .................................................. 39 (3 V Operation) .......................................................................... 17 AD7707 to 8XC51 Interface ..................................................... 40 On-Chip Registers .......................................................................... 18 Code For Setting Up the AD7707 ................................................ 41 Communications Register (RS2, RS1, RS0 = 0, 0, 0) ............. 18 C Code for Interfacing AD7707 to 68HC11 ........................... 41 Calibration Sequences .................................................................... 23 Applications Information .............................................................. 43 Circuit Description ......................................................................... 24 Data Acquisition ......................................................................... 43 Analog Input ................................................................................... 25 Smart Valve/Actuator Control .................................................. 43 Analog Input Ranges .................................................................. 25 Pressure Measurement ............................................................... 45 Input Sample Rate ...................................................................... 26 Thermocouple Measurement ................................................... 45 Bipolar/Unipolar Inputs ............................................................ 26 RTD Measurement ..................................................................... 45 Reference Input ............................................................................... 27 Chart Recorders .......................................................................... 46 Digital Filtering ............................................................................... 28 Accommodating Various High Level Input Ranges .............. 46 Filter Characteristics .................................................................. 28 Typical Input Currents ............................................................... 46 Postfiltering ................................................................................. 29 Output Noise For High Level Input Channel, AIN3 ................. 47 Analog Filtering .......................................................................... 29 5 V Operation ............................................................................. 47 Calibration ....................................................................................... 30 3 V Operation ............................................................................. 48 Self-Calibration ........................................................................... 30 Outline Dimensions ....................................................................... 49 System Calibration ..................................................................... 30 Ordering Guide .......................................................................... 50 Rev. B Page 2 of 52