ADC. AD7985 Datasheet

AD7985 Datasheet PDF


Part

AD7985

Description

PulSAR 15.5 mW ADC

Manufacture

Analog Devices

Page 28 Pages
Datasheet
Download AD7985 Datasheet


AD7985 Datasheet
Data Sheet
16-Bit, 2.5 MSPS, PulSAR
15.5 mW ADC in LFCSP
AD7985
FEATURES
16-bit resolution with no missing codes
Throughput: 2.5 MSPS (TURBO high), 2.0 MSPS (TURBO low)
Low power dissipation
15.5 mW at 2.5 MSPS, with external reference
28 mW at 2.5 MSPS, with internal reference
INL: ±0.7 LSB typical, ±1.5 LSB maximum
SNR
88.5 dB, with on-chip reference
90 dB, with external reference
4.096 V internal reference: typical drift of ±10 ppm/°C
Pseudo differential analog input voltage range
0 V to VREF with VREF up to 5.0 V
Allows use of any input range
No pipeline delay
Logic interface: 1.8 V/2.5 V/2.7 V
Proprietary serial interface SPI-/QSPI™-/MICROWIRE™-/DSP-
compatible1
Ability to daisy-chain multiple ADCs with busy indicator
20-lead, 4 mm × 4 mm LFCSP
APPLICATIONS
Battery-powered equipment
Communications
ATE
Data acquisition systems
Medical instruments
0V
TO
VREF
APPLICATION DIAGRAM
1.8V
TO
5V 2.5V 2.7V
BVDD AVDD, VIO
DVDD TURBO
IN+ SDI
AD7985
IN–
SCK
SDO
GND REF
CNV
10µF
VIO
3- OR 4-WIRE
INTERFACE:
SPI, CS,
DAISY CHAIN
(TURBO = LOW)
NOTES
1. GND REFERS TO REFGND, AGND, AND DGND.
Figure 1.
GENERAL DESCRIPTION
The AD79851 is a 16-bit, 2.5 MSPS successive approximation
analog-to-digital converter (SAR ADC). It contains a low power,
high speed, 16-bit sampling ADC, an internal conversion clock,
an internal reference (and buffer), error correction circuits, and
a versatile serial interface port. On the rising edge of CNV, the
AD7985 samples an analog input, IN+, between 0 V and REF
with respect to a ground sense, IN−. The AD7985 features a
very high sampling rate turbo mode (TURBO is high) and a
reduced power normal mode (TURBO is low) for low power
applications where the power is scaled with the throughput.
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 −40°C to +85°C.
Table 1. MSOP, LFCSP, 14-/16-/18-Bit PulSAR® ADCs1
Type
100 kSPS
250 kSPS
14-Bit
AD7940
AD79422
16-Bit
AD7680
AD76852
AD7683
AD76872
AD7684
AD7694
18-Bit
AD76912
1 Protected by U. S. Patent 6,703,961.
400 kSPS to 500 kSPS
AD79462
AD76862
AD76882
AD76932
AD76902
≥1000 kSPS
AD79802
AD79832
AD79853
AD79822
AD79842
AD79863
ADC Driver
ADA4941-1
ADA4841-1
AD8021
ADA4941-1
ADA4841-1
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
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rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
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Tel: 781.329.4700 ©2009–2016 Analog Devices, Inc. All rights reserved.
Technical Support
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AD7985 Datasheet
AD7985
TABLE OF CONTENTS
Features .............................................................................................. 1 
Applications....................................................................................... 1 
Application Diagram........................................................................ 1 
General Description ......................................................................... 1 
Revision History ............................................................................... 2 
Specifications..................................................................................... 3 
Timing Specifications .................................................................. 5 
Absolute Maximum Ratings............................................................ 6 
ESD Caution.................................................................................. 6 
Pin Configuration and Function Descriptions............................. 7 
Typical Performance Characteristics ............................................. 9 
Terminology .................................................................................... 12 
Theory of Operation ...................................................................... 13 
Circuit Information.................................................................... 13 
Converter Operation.................................................................. 13 
Conversion Modes of Operation.............................................. 13 
Typical Connection Diagram ................................................... 14 
REVISION HISTORY
3/16—Rev. B to Rev. C
Changes to Table 1............................................................................ 1
Change to Endnote 3, Table 1 ......................................................... 3
Change to Signal-to-Noise-and-Distortion Ratio Parameter,
Table 2 ................................................................................................ 3
Deleted Endnote 4, Table 2.............................................................. 3
Changes to Figure 4.......................................................................... 7
Changes to Figure 23...................................................................... 14
Changes to Driver Amplifier Choice Section ............................. 15
Change to Reference Decoupling Section ................................... 16
Changes to Reading During Conversion, Fast Host (Turbo or
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
Data Sheet
Analog Inputs ............................................................................. 15 
Driver Amplifier Choice ........................................................... 15 
Voltage Reference Input ............................................................ 16 
Power Supply............................................................................... 16 
Digital Interface .............................................................................. 17 
Data Reading Options ............................................................... 18 
CS Mode, 3-Wire Without Busy Indicator ............................. 19 
CS Mode, 3-Wire with Busy Indicator .................................... 20 
CS Mode, 4-Wire Without Busy Indicator ............................. 21 
CS Mode, 4-Wire with Busy Indicator .................................... 22 
Chain Mode Without Busy Indicator ...................................... 23 
Chain Mode with Busy Indicator ............................................. 24 
Applications Information .............................................................. 25 
Layout .......................................................................................... 25 
Evaluating the AD7985 Performance ...................................... 25 
Outline Dimensions ....................................................................... 27 
Ordering Guide .......................................................................... 27 
7/14—Rev. A to Rev. B
Added Patent Endnote......................................................................1
Changes to Figure 21...................................................................... 13
Changes to Data Reading Options Section................................. 18
Updated Outline Dimensions....................................................... 27
8/10—Rev. 0 to Rev. A
Change to Table 4, Conversion Time: CNV Rising Edge
to Data Available................................................................................5
9/09—Revision 0: Initial Version
Rev. C | Page 2 of 28


Features Datasheet pdf 16-Bit, 2.5 MSPS, PulSAR 15.5 mW ADC in LFCSP AD7985 FEATURES 16-bit resolution with no missing codes Throughput: 2.5 MSPS (TURBO high), 2.0 MSPS (TURBO low) Low power dissipation 15.5 mW at 2.5 M SPS, with external reference 28 mW at 2 .5 MSPS, with internal reference INL: 0.7 LSB typical, ±1.5 LSB maximum SNR 88.5 dB, with on-chip reference 90 dB, with external reference 4.096 V intern al reference: typical drift of ±10 ppm /°C Pseudo differential analog input v oltage range 0 V to VREF with VREF up t o 5.0 V Allows use of any input range N o pipeline delay Logic interface: 1.8 V /2.5 V/2.7 V Serial interface: SPI-/QSP I™-/MICROWIRE™-/DSP-compatible Abil ity to daisy-chain multiple ADCs with b usy indicator 20-lead, 4 mm × 4 mm LFC SP (QFN) APPLICATION DIAGRAM 5V 2.5V 1 .8V TO 2.7V 0V TO VREF IN+ IN– VIO BVDD AVDD, DVDD TURBO VIO 3- OR 4-WIR E INTERFACE: SPI, CS, DAISY CHAIN (TURB O = LOW) AD7985 GND REF 10µF SDI SCK SDO CNV NOTES 1. GND REFERS TO REFGND, AGND, AND DGND. Figure 1. GENERA.
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