16-Bit, 2.5 MSPS, PulSAR 15.5 mW ADC in LFCSP Data Sheet AD7985 FEATURES APPLICATION DIAGRAM 1.8V 16-bit resolution with no missing codes TO 5V 2.5V 2.7V Throughput: 2.5 MSPS (TURBO high), 2.0 MSPS (TURBO low) Low power dissipation BVDD VIO AVDD, 15.5 mW at 2.5 MSPS, with external reference DVDD 0V VIO TURBO 28 mW at 2.5 MSPS, with internal reference TO IN+ 3- OR 4-WIRE SDI V REF AD7985 INL: 0.7 LSB typical, 1.5 LSB maximum INTERFACE: SCK IN SPI, CS, SNR SDO DAISY CHAIN CNV (TURBO = LOW) GND REF 88.5 dB, with on-chip reference 90 dB, with external reference 10F 4.096 V internal reference: typical drift of 10 ppm/C Pseudo differential analog input voltage range NOTES 0 V to V with V up to 5.0 V REF REF 1. GND REFERS TO REFGND, AGND, AND DGND. Allows use of any input range Figure 1. No pipeline delay GENERAL DESCRIPTION Logic interface: 1.8 V/2.5 V/2.7 V 1 Proprietary serial interface SPI-/QSPI-/MICROWIRE-/DSP- The AD7985 is a 16-bit, 2.5 MSPS successive approximation 1 compatible analog-to-digital converter (SAR ADC). It contains a low power, Ability to daisy-chain multiple ADCs with busy indicator high speed, 16-bit sampling ADC, an internal conversion clock, 20-lead, 4 mm 4 mm LFCSP an internal reference (and buffer), error correction circuits, and a versatile serial interface port. On the rising edge of CNV, the APPLICATIONS AD7985 samples an analog input, IN+, between 0 V and REF Battery-powered equipment with respect to a ground sense, IN. The AD7985 features a Communications very high sampling rate turbo mode (TURBO is high) and a ATE reduced power normal mode (TURBO is low) for low power Data acquisition systems applications where the power is scaled with the throughput. Medical instruments In normal mode (TURBO is low), the SPI-compatible serial inter- face also features the ability, using the SDI input, to daisy-chain several ADCs on a single 3-wire bus and provide an optional busy indicator. It is compatible with 1.8 V, 2.5 V, and 2.7 V supplies using the separate VIO supply. The AD7985 is available in a 20-lead LFCSP with operation specified from 40C to +85C. 1 Protected by U. S. Patent 6,703,961. 1 Table 1. MSOP, LFCSP, 14-/16-/18-Bit PulSAR ADCs Type 100 kSPS 250 kSPS 400 kSPS to 500 kSPS 1000 kSPS ADC Driver 2 2 14-Bit AD7940 AD7942 AD7946 2 2 2 16-Bit AD7680 AD7685 AD7686 AD7980 ADA4941-1 2 2 2 AD7683 AD7687 AD7688 AD7983 ADA4841-1 2 3 AD7684 AD7694 AD7693 AD7985 AD8021 2 2 2 18-Bit AD7691 AD7690 AD7982 ADA4941-1 2 AD7984 ADA4841-1 3 AD7986 AD8021 1 See www.analog.com for the latest selection of PulSAR ADCs and ADC drivers. 2 Pin for pin compatible with all other devices marked with this endnote. 3 The AD7985 and AD7986 are pin for pin compatible. Rev. C Document Feedback 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 20092016 Analog Devices, Inc. All rights reserved. license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Technical Support www.analog.com Trademarks and registered trademarks are the property of their respective owners. 07947-001AD7985 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Analog Inputs ............................................................................. 15 Applications ....................................................................................... 1 Driver Amplifier Choice ........................................................... 15 Application Diagram ........................................................................ 1 Voltage Reference Input ............................................................ 16 General Description ......................................................................... 1 Power Supply ............................................................................... 16 Revision History ............................................................................... 2 Digital Interface .............................................................................. 17 Specif icat ions ..................................................................................... 3 Data Reading Options ............................................................... 18 Timing Specifications .................................................................. 5 CS Mode, 3-Wire Without Busy Indicator ............................. 19 Absolute Maximum Ratings ............................................................ 6 CS Mode, 3-Wire with Busy Indicator .................................... 20 ESD Caution .................................................................................. 6 CS Mode, 4-Wire Without Busy Indicator ............................. 21 Pin Configuration and Function Descriptions ............................. 7 CS Mode, 4-Wire with Busy Indicator .................................... 22 Typical Performance Characteristics ............................................. 9 Chain Mode Without Busy Indicator ...................................... 23 Terminology .................................................................................... 12 Chain Mode with Busy Indicator ............................................. 24 Theory of Operation ...................................................................... 13 Applications Information .............................................................. 25 Circuit Information .................................................................... 13 Layout .......................................................................................... 25 Converter Operation .................................................................. 13 Evaluating the AD7985 Performance ...................................... 25 Conversion Modes of Operation .............................................. 13 Outline Dimensions ....................................................................... 27 Typical Connection Diagram ................................................... 14 Ordering Guide .......................................................................... 27 REVISION HISTORY 3/16Rev. B to Rev. C 7/14Rev. A to Rev. B Changes to Table 1 ............................................................................ 1 Added Patent Endnote ...................................................................... 1 Change to Endnote 3, Table 1 ......................................................... 3 Changes to Figure 21 ...................................................................... 13 Change to Signal-to-Noise-and-Distortion Ratio Parameter, Changes to Data Reading Options Section ................................. 18 Table 2 ................................................................................................ 3 Updated Outline Dimensions ....................................................... 27 Deleted Endnote 4, Table 2 .............................................................. 3 Changes to Figure 4 .......................................................................... 7 8/10Rev. 0 to Rev. A Changes to Figure 23 ...................................................................... 14 Change to Table 4, Conversion Time: CNV Rising Edge to Data Available ................................................................................ 5 Changes to Driver Amplifier Choice Section ............................. 15 Change to Reference Decoupling Section ................................... 16 Changes to Reading During Conversion, Fast Host (Turbo or 9/09Revision 0: Initial Version Normal Mode) Section and Split-Reading, Any Speed Host (Turbo or Normal Mode) Section ................................................ 18 Changes to Figure 31 ...................................................................... 21 Updated Outline Dimensions ....................................................... 27 Changes to Ordering Guide .......................................................... 27 Rev. C Page 2 of 28