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In This Issue

2Editors Notes; New Product Introductions

3 PLC Evaluation Board Simplifies Design of Industrial Process-Control Systems

11Skin Impedance Analysis Aids Active and Passive Transdermal Delivery

13AccelerometersFantasy and Reality

15Digital Isolator Simplifies USB Isolation in Medical and Industrial Applications

19Automated Calibration Technique Reduces DAC Offset to Less Than 1 mV

21Rules of the Road for High-Speed Differential ADC Drivers

Volume 43, Number 2, 2009 A forum for the exchange of circuits, systems, and software for real-world signal processing


2/322 ISSN 0161-3626 Analog Devices, Inc. 2010

Editors Notes

IN THIS ISSUE

PLC Evaluation Board Simplifes Design o Industrial Process-

Control Systems

The applications or industrial process-control systems

range rom simple traic control to complex electrical

power grids, rom environmental control systems to oil-

reiner y process control. The intelligence o these systems

lies in their measurement and control units. The two most

common computer-based systems to control machines

and processes are programmable logic control lers and

distributed control systems. Page 3.

Skin Impedance Analysis Aids Active and Passive Transdermal

Delivery

Pharmaceut ical i rms are developing a l ternat ives to

injections. Transdermal methods, which eature noninvasive

delivery o medication through a patients skin, overcome

the protective bar rier in one o two ways: passive absorption

and active penetration. Skin impedance analysis acilitates

proper dosing. Page 11.

AccelerometersFantasy and Reality

High sensitivity, small size, low cost, rugged packaging, and theability to measure both static and dynamic acceleration have

made numerous new applications o surace micromachined

accelerometers possible. Many o these were not anticipated

because they were not thought o as classic accelerometer

applications. New applications are limited only by the

imagination o designers. Page 13.

Digital Isolator Simplifes USB Isolation in Medical and

Industrial Applications

Despite its low speed and point-to-point nature, RS-232 was

tolerated in medical and industrial applications because it

was universally available, well supported, and allowed easy

implementation o the required isolation. The ADuM4160

digital isolator allows simple, inexpensive isolation o ull-and low-speed USB peripheralsincluding the D+ and

D linesincreasing the useulness o USB in medical and

industrial applications. Page 15.

Automated Calibration Technique Reduces DAC Oset to Less

Than 1 mV

The AD5360 16-bit, 16-channel DAC is actory tr immed, but

an oset o several millivolts can still exist. This idea shows

how a simple sotware algorithm can reduce an unknown

oset to less than 1 mV. This technique can be used or actory

calibration, or or oset correction at any point in the DACs

lie cycle. Page 19.

Rules o the Road or High-Speed Dierential ADC DriversMost modern high-perormance ADCs use dierential inputs

to reject common-mode noise and intererence, increase

dynamic range by a actor o two, and improve overall

perormance. ADC driverscircuits oten speciical ly

designed to provide dierential signalsperorm many

important unctions including amplitude scaling, single-

ended-to-dierential conversion, buering, common-mode

oset adjustment, and iltering. Page 21.

Dan Sheingold[[email protected]]

Scott Wayne [[email protected]]

Analog Dialogue, www.analog.com/analogdialogue, the technical magazine oAnalog Devices, discusses products, applications, technology, and techniquesor analog, digital, and mixed-signal processing. Published continuouslyor 43 yearsstarting in 1967it is currently available in two versions.Monthly editions oer technical articles; timely inormation including recentapplication notes, new-product bries, pre-release products, webinars andtutorials, and published articles; and potpourri, a universe o links to importantand relevant inormation on the Analog Devices website, www.analog.com.Printable quarterly issues eature collections o monthly articles. For historybus, the Analog Dialogue archive includes all regular editions, starting withVolume 1, Number 1 (1967), and three special anniversary issues. I you wishto subscribe, please go to www.analog.com/analogdialogue/subscribe.html .Your comments are always welcome; please send messages [email protected] toDan Sheingold, Editor [[email protected]]or Scott Wayne, Publisher and Managing Editor [[email protected]].

PRODUCT INTRODUCTIONS: VOLUME 43, NUMBER 2Data sheets or all ADI products can be ound by entering the part

number in the search box at www.analog.com.

AprilDAC, current-output, 14-bit, 2500-MSPS ...............................AD9739Multiplexer, iCMOS, 4:1, 1- ............................................ADG1604Switch, iCMOS, dual SPDT, 1- ........................................ADG1636Switches, iCMOS, quad SPST, 1- ....ADG14611/ADG1612/ADG1613

MayAccelerometer, gyroscope, and magnetometer, 3-axis ....... ADIS16405

Buer, clock, ultraast, 2-input, 12-output .........................ADCLK954Comparator, voltage, very ast, LVDS ....................................AD8465Controller, touch-screen, low-voltage ......................................AD7889DACs, current-output, 12-/16-bit ..............................AD5410/AD5420DAC, voltage-output, quad, 12-bit ........................................ AD5724REnergy Meters, single-phase ...............................ADE5566/ADE5569Gyroscope, yaw-rate ......................................................... ADXRS622

JuneAccelerometer, gyroscope, and magnetometer, 3-axis ....... ADIS16400Amplifer, audio, Class-D, 2 2-W ......................................SSM2356Amplifer, dierence, unity-gain, wide supply range ................AD8276Amplifer, instrumentation, micropower .................................AD8236Amplifer, operational, dual, wideband .............................ADA4692-2Amplifers, RF/IF, ultralow-distortion ................. ADL5561/ADL5562Amplifer, variable-gain, 1 MHz to 1.2 GHz .........................ADL5331Amplifer, variable-gain, quad, 235-MHz ................................AD8264ADC, pipelined, quad, 12-bit, 170-MSPS/210-MSPS ..............AD9639ADC, -, 24-bit, 4.8-kHz ......................................................AD7192ADC, -, 24-bit programmable gain, data rate .......................AD7191ADC, successive-approximation, 18-bit, 2-MSPS .....................AD7986ADC, successive-approximation, dual, 14-bit, 4.2-MSPS ..........AD7357ADCs, pipelined, dual, 14-/16-bit, 125-MSPS ........... AD9258/AD9268ADCs, -, 24-/20-bit, pin-programmable ................ AD7780/AD7781Buer, clock anout, 6 LVPECL outputs ...........................ADCLK946Buer, clock anout, 12 LVDS/24 CMOS outputs ............. ADCLK854Controller, digital, isolated power supplies ........................... ADP1043Converter, dc-to-dc, step-down, 600 mA ............................. ADP2109Converter, dc-to-dc, synchronous, step-down, 600 mA ......... ADP2121Converters, dc-to-dc, step-up, 650 kHz/1300 kHz .. ADP1612/ADP1613DAC, RF, 14-bit, 2400-MSPS, 4-channel QAM .......................AD9789DACs, current- and voltage output, 12-/16-bit ........... AD5412/AD5422Detector, rms power, 50-dB, 50 Hz to 6 GHz .........................AD8363

Driver, 7-channel LED ....................................................... ADP8860Drivers, dierential ADC, single and dual ......ADA4950-1/ADA4950-2Generator, multiservice clock .................................................AD9551Generator/synchronizer, network clock ................................. AD9548Isolators, digital, 4-channel, 5-kV ........................................................

.................................................ADuM4400/ADuM4401/ADuM4402Microcontroller, precision analog, two 24-bit ADCs .......... ADuC7060Potentiometers, digital, 256-/1024-position .............. AD5291/AD5292Potentiometer, digital, 1024-position .....................................AD5293Processor, digital audio, exible routing matrix ..................ADAU1446Processors, embedded, Blackfn .........ADSP-BF52x/ADSP-BF52xCPower Management Unit, imaging ..................................... ADP5020Sensor, impact, programmable .......................................... ADIS16240Sensors, temperature, 16-bit ................................ADT7310/ADT7410Tuner, mobile TV, ISDB-T ..............................................ADMTV202
mailto:[email protected]:[email protected]://www.analog.com/analogdialoguehttp://www.analog.com/http://www.analog.com/analogdialogue/subscribe.htmlmailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://www.analog.com/analogdialogue/subscribe.htmlhttp://www.analog.com/http://www.analog.com/analogdialoguemailto:[email protected]:[email protected]


3/32Analog Dialogue Volume 43 Number 2 3

PLC Evaluation BoardSimplifes Design o IndustrialProcess-Control SystemsBy Colm Slattery, Derrick Hartmann, and Li Ke

Introduction

The applications or industrial process-control systems are diverse,

ranging rom simple trafc control to complex electrical powergrids, rom envi ronmental control systems to oil-refnery process

control. The intelligence o these automated systems lies in their

measurement and control units. The two most common computer-

based systems to control machines and processes, dealing with the

various analog and digital inputs and outputs, are programmable

logic controllers1 (PLCs) and distributed control systems2 (DCSs).

These systems comprise power supplies, central processor units

(CPUs), and a variety o analog-input, analog-output, digital-

input, and digital-output modules.

The standard communications protocols have existed or many

years; the ranges o analog variables are dominated by 4 mA

to 20 mA, 0 V to 5 V, 0 V to 10 V, 5 V, and 10 V. Therehas been much discussion about wireless solutions or next-

generation systems, but designers still claim that 4 mA to 20 mAcommunications and control loops will continue to be used or

many years. The criteria or the next generation o these systems

will include higher perormance, smaller size, better system

diagnostics, higher levels o protection, and lower costall actors

that will help manuacturers dierentiate their equipment rom

that o their competitors.

We will discuss the key perormance requirements o process-

control systems and the analog input/output modules they

containand will introduce an industrial process-control

evaluation system that integrates these building blocks using the

latest integrated-circuit technology. We also look at the challenges

o designing a robust system that will withstand the electrical ast

transients (EFTs), electrostatic discharges (ESDs), and voltage

surges ound in industrial environmentsand present test data

that verifes design robustness.

PLC Overview with Application Example

Figure 1 shows a basic process-control system building block.

A process variable, such as ow rate or gas concentration, is

monitored via the input module. The inormation is processed by

the central control unit; and some action is taken by the output

module, which, or example, drives an actuator.

ACTUATORS

INPUT

MODULE(S)

CENTRAL

CONTROL UNIT

OUTPUT

MODULE(S)

SENSORS

PLCPROGRAM

Figure 1. Typical top-level PLC system.

Figure 2 shows a typical industrial subsystem o this type. Here a

CO2 gas sensor determines the concentration o gas accumulated in

a protected area and transmits the inormation to a central control

point. The control unit consists o an analog input module that

conditions the 4 mA to 20 mA signal rom the sensor, a central

processing unit, and an analog output module that controls the

required system variable. The current loop can handle large

capacitive loadsoten ound on hundreds-o-meters long

communications paths experienced in some industrial systems

The output o the sensor element, representing gas concentration

levels, is transormed into a standard 4 mA to 20 mA signal, which

is transmitted over the current loop. This simplifed example

shows a single 4 mA to 20 mA sensor output connected to a single-

channel input module and a single 0 V to 10 V output. In practice

most modules have multiple channels and confgurable ranges.

The resolution o input/output modules typically ranges rom

12- to 16 bits, with 0.1% accuracy over the industrial temperature

range. Input ranges can be as small as 10 mV or bridge transducerand as large as 10 V or actuator controllersor 4 mA to 20 mAcurrents in process-control systems. Analog output voltage and

current ranges typically include 5 V, 10 V, 0 V to 5 V, 0 V to 10 V4 mA to 20 mA, and 0 mA to 20 mA. Settling-time requirements

or digital-to-analog converters (DACs) vary rom 10 s to 10 msdepending on the application and the circuit load.

0V TO 10V

4mA TO 20mA

CPU

OUTPUT MODULE

INPUT MODULE

RACK

GAS

SENSOR

Figure 2. Gas sensor.

The 4 mA to 20 mA range is mapped to represent the normal gas

detection range; current values outside this range can be used to

provide ault-diagnostic inormation, as shown in Table 1.

Table 1. Assigning Currents Outside

the 4 mA to 20 mA Output Range

Current Output (mA) Status

0.0 Unit ault0.8 Unit warm-up

1.2 Zero drit ault

1.6 Calibration ault

2.0 Unit spanning

2.2 Unit zeroing

4 to 20 Normal measuring mode

4.0 Zero gas level

5.6 10% ull scale

8.0 25% ull scale

12 50% ull scale

16 75% ull scale

20 Full scale

>20 Overrange

PLC Evaluation System

The PLC evaluation system3 described here integrates all the stages

needed to generate a complete input/output design. It contains our

ully isolated ADC channels, an ARM7 microprocessor with

RS-232 interace, and our ully isolated DAC output channels

The board is powered by a dc supply. Hardware-confgurable

input ranges include 0 V to 5 V, 0 V to 10 V, 5 V, 10 V, 4 mAto 20 mA, 0 mA to 20 mA, 20 mA, as well as thermocouple andRTD. Sotware-programmable output ranges include 0 V to 5 V

0 V to 10 V, 5 V, 10 V, 4 mA to 20 mA, 0 mA to 20 mA, and0 mA to 24 mA.
http://en.wikipedia.org/wiki/Programmable_logic_controllerhttp://en.wikipedia.org/wiki/Programmable_logic_controllerhttp://en.wikipedia.org/wiki/Distributed_control_systemhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://en.wikipedia.org/wiki/Distributed_control_systemhttp://en.wikipedia.org/wiki/Programmable_logic_controllerhttp://en.wikipedia.org/wiki/Programmable_logic_controller


4/324 Analog Dialogue Volume 43 Number 2

ANALOG SIGNALS

SENSOR INPUTS

RTDTCGAS

VOLTAGE INPUTS(FLOW, PRESSURE)

0V TO 5V, 0V TO 10V5V, 10V

CURRENT INPUTS(COMMUNICATIONS)

0mA TO 24mA4mA TO 20mA

ANALOG OUTPUTS

VOLTAGE OUTPUTS

0V TO 5V, 0V TO 10V5V, 10V

CURRENT OUTPUTS

0mA TO 24mA4mA TO 20mA

ANALOG INPUT/OUTPUT MODULE

PLC MODULEBOARD

Figure 3. Analog input/output module.

Output Module: Table 2 highlights some key specifcations o

PLC output modules. Since the true system accuracy lies within

the measurement channel (ADC), the control mechanism (DAC)

requires only enough resolution to tune the output. For high-end

systems, 16-bit resolution is required. This requirement is actually

quite easy to satisy using standard digital-to-analog architectures.

Accuracy is not crucial; 12-bit integral nonlinearity (INL) is

generally adequate or high-end systems.

Calibrated accuracy o 0.05% at 25C is easily achievable by

overranging the output and tr imming to achieve the desired value.

Todays 16-bit DACs, such as the AD5066,4 oer 0.05 mV typical

oset error and 0.01% typical gain error at 25C, eliminating theneed or calibration in many cases. Total accuracy error o 0.15%

sounds manageable but is actually quite aggressive when specifed

over temperature. A 30 ppm/C output drit can add 0.18% errorover the industrial temperature range.

Table 2. Output Module Specifcations

System Specifcation Requirement

Resolution 16 bits

Calibrated Accuracy 0.05%

Total Module Accuracy Error 0.15%

Open-Circuit Detection Yes

Short-Circuit Detection Yes

Short-Circuit Protection Yes

Isolation Yes

Output modules may have current outputs, voltage outputs, or a

combination. A classical solution that uses discrete components

to implement a 4 mA to 20 mA loop is shown in Figure 4. The

AD5660 16-bit nanoDAC converter provides a 0 V to 5 V output

that sets the current through sense resistor, RS, and thereore,

through R1. This current is mirrored through R2.

Setting RS = 15 k, R1 = 3 k, R2 = 50 and using a 5-V DACwill result in IR2 = 20 mA max.

VDD

AD5660

16-BIT

DAC

2.5V

REF

AMP

AMP

R1

RS

R2

VDD

TERMINAL

SCREWS

VDAC

4mA TO

20mA

Figure 4. Discrete 4 mA to 20 mA implementation.

This discrete design suers rom many drawbacks: Its high

component count engenders signifcant system complexity, board

size, and cost. Calculating total error is difcult, with multiple

components adding varying degrees o error with coefcients

that can be o diering polarities. The design does not provide

short-circuit detection/protection or any level o ault diagnostics.

It does not include a voltage output, which is required in many

industrial control modules. Adding any o these eatures would

increase the design complexity and the number o components. A

better solution would be to integrate all o the above on a single IC,

such as the AD5412/AD5422low-cost, high-precision, 12-/16-bit

digital-to-analog converters. They provide a solution that oers a

ully integrated programmable current source and programmablevoltage output designed to meet the requirements o industrial

process-control applications.

LATCH

CLEAR

CLEAR

SELECT

SCLK

SDIN

SDO

INPUT

SHIFT

REGISTER

AND

CONTROL

POWER

ONRESET

16-BIT

DAC

16

R1

R2 R3

BOOST

AVDDAVSS

REFIN GND CCOMP2 CCOMP1

DVSSDVCC SELECT

IOUT

FAULT

RANGE

SCALING

REFOUT

VREF +VSENSE

RSET

VOUT

VSENSE

AD5422

Figure 5. AD5422 programmable voltage/current output.

The output current range is programmable to 4 mA to 20 mA,

0 mA to 20 mA, or 0 mA to 24 mA overrange unction. A voltage

output, available on a separate pin, can be confgured to provide

0 V to 5 V, 0 V to 10 V, 5 V, or 10 V ranges, with a 10%overrange available on all ranges. Analog outputs are short-circuit

protected, a critical eature in the event o miswired outputsor

example, when the user connects the output to ground instead o to

the load. The AD5422 also has an open-circuit detection eaturethat monitors the current-output channel to ensure that no ault

has occurred between the output and the load. In the event o an

open circuit, the FAULT pin will go active, alerting the system

controller. The AD5750 programmable current/voltage output

driver eatures both short-circuit detection and protection.
http://www.analog.com/en/digital-to-analog-converters/da-converters/ad5066/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5660/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5412/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5422/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5422/products/product.htmlhttp://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifiers/ad5750/products/product.htmlhttp://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifiers/ad5750/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5422/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5412/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5660/products/product.htmlhttp://www.analog.com/en/digital-to-analog-converters/da-converters/ad5066/products/product.html



Figure 6 shows the output module used in the PLC evaluation

system. While earlier systems typically needed 500 V to 1 kV o

isolation, today >2 kV is generally required. The ADuM1401

digital isolator usesiCoupler5 technology to provide the necessary

isolation between the MCU and remote loads, or between the

input/output module and the backplane. Three channels o the

ADuM1401 communicate in one direction; the ourth channel

communicates in the opposite direction, providing isolated data

readback rom the converters. For newer industrial designs, the

ADuM3401 and other members o its amily o digital isolators

provide enhanced system-level ESD protection.The AD5422 generates its own logic supply (DVCC), which can be

directly connected to the feld side o the ADuM1401, eliminating

the need to bring a logic supply across the isolation barrier. The

AD5422 includes an internal sense resistor, but an external resistor

(R1) can be used when lower drit is required. Because the sense

resistor controls the output current, any drit o its resistance

will aect the output. The typical temperature coefcient o the

internal sense resistor is 15 ppm/C to 20 ppm/C, which could add0.12% error over a 60C temperature range. In high-perormancesystem applications, an external 2-ppm/C sense resistor could beused to keep drit to less than 0.016%.

The AD5422 has an internal 10-ppm/C max voltage reerence thatcan be enabled on all our output channels in the PLC evaluation

system. Alternatively, theADR445ultralow-noise XFET voltage

reerence, with its 0.04% initial accuracy and 3 ppm/C, can beused on two output channels, allowing perormance comparison

and a choice o internal vs. external reerence, depending on the

total required system perormance.

Input Module: The input module design specifcations are similar

to those o the output module. High resolution and low noise are

generally important. In industrial applications, a dierential inpu

is required when measuring low-level signals rom thermocouples

strain gages, and bridge-type pressure sensors to reject common

mode intererence rom motors, ac power lines, or other noise

sources that inject noise into the analog inputs o the analog-to

digital converter (ADCs).

Sigma-delta ADCs are the most popular choice or input modules

as they provide high accuracy and resolution. In addition, interna

programmable-gain amplifers (PGAs) allow small input signals to

be measured accurately. Figure 7 shows the input module design

used in the evaluation system. The AD7793 3-channel, 24-bisigma-delta ADC is confgured to accommodate a large range

o input signals, such as 4 mA to 20 mA, 10 V, as well as smalsignal inputs directly rom sensors.

Care was taken to allow this universal input design to be easily

adapted or RTD/thermocouple modules. As shown, two inpu

terminal blocks are provided per input channel. One input allows

or a direct connection to the AD7793. The user can program

the interna l PGA to provide analog gains up to 128. The second

input allows the signal to be conditioned through the AD8220

JFET-input inst rumentation amplifer. In this case, the input

signal is attenuated, amplifed, and level shited to provide a

single-ended input to the ADC. In addition to providing the

level shiting unction, the AD8220 also eatures very good

common-mode rejection, important in applications having a

wide dynamic range.

The low-power, high-perormance AD7793 consumes



To measure a 4 mA to 20 mA input signal, a low-drit precision

resistor can be switched (S4) into the circuit. In this design, its

resistance is 250 , but any value can be used as long as thegenerated voltage is within the input range o the AD8220. S4 is

let open when measuring a voltage.

Isolation is required or most input-module designs. Figure 7

shows how isolation was implemented on one channel o the PLC

evaluation system. The ADuM5401 4-channel digital isolator uses

isoPower6 technology to provide 2.5-kV rms signal and power

isolation. In addition to providing our isolated signal channels,

the ADuM5401 also contains an isolated dc-to-dc converter thatprovides a regulated 5-V, 500-mW output to power the analog

circuitry o the input module.

Complete System: An overview o the complete system is shown

in Figure 8. The ADuC7027 precision analogmicrocontroller7

is the main system controller. Featuring the ARM7TDMI core,

its 32-bit architecture allows easy interace to 24-bit ADCs. It

also supports a 16-bit thumb mode, which allows or greater code

density i required. The ADuC7027 has 16 kB o on-board ash

memory and allows interacing to up to 512 kB external memory.

The ADP3339 high-accuracy, low-dropout regulator (LDO)

provides the regulated supply to the microcontroller.

Communication between the evaluation board and the PC

is provided via the ADM3251E isolated RS-232 transceiver.The ADM3251E incorporates isoPower technologymaking

a separate isolated dc-to-dc converter unnecessary. It is ideally

suited to operation in electrically harsh environments or where

RS-232 cables are requently plugged in or unplugged, as the

RS-232 pins, Rx and Tx, are protected against electrostatic

discharges o up to 15 kV.

Evaluation System Sotware and Evaluation Tools: The

evaluation system is very versatile. Communication with the PC is

achieved using LabVIEW.8 The frmware or the microcontroller

(ADuC7027) is written in C, which controls the low-level

commands to and rom the ADC and DAC channels.

Figure 9 shows the main screen interace. Pull-down menus on the

let side allow the user to choose active ADC and DAC channels.

Under each ADC and DAC menu there is a pull-down range

menu, which is used to select the desired input and output ranges

to be measured and controlled. The ollowing input and output

ranges are available: 4 mA to 20 mA, 0 mA to 20 mA, 0 mAto 24 mA, 0 V to 5 V, 0 V to 10 V, 5 V, and 10 V. Small signalinput ranges can also be accommodated directly on the ADC by

using its internal PGA.

Figure 9. Evaluation sotware main screen controller.

AD7793 ADuM1401

ISOLATED

BIPOLARISOLATEDDC-TO-DC

AD8220

ADR441

IOUT1

IOUT2

+5V

RREF

15V

V/I INPUTS, BIPOLAR SUPPLY, HIGH PERFORMANCE

AD7793

ADuM5401

ISOLATED

AD8220

IOUT1

IOUT2RREF

V/I INPUTS, SINGLE SUPPLY, LOWER COST

+24V

+24V

+5V

SPI

ADuC

7027

ADP33

39

ISODC-TO-DC

AD5422

IOUTRANGESCALE

VOUTRANGESCALE

DAC

SPI

OVERTEMPDETECT

OPENDETECT

4mA TO 20mA,0mA TO 24mA

0V TO 5V,0V TO 10V,5V,10V

ADuM1401

ISOLATED

ADR445ISO

DC-TO-DC,15V

(>30mA)

+3.3V

AD5422

IOUTRANGESCALE

VOUTRANGESCALE

DAC

REF

SPI

OVERTEMPDETECT

OPENDETECT

4mA TO 20mA,0mA TO 24mA

0V TO 5V,0V TO 10V,5V,10V

ADuM1401

ISOLATED

(>30mA)

ISO DC-TO-DC, 15V

+5V

+5V

ADM3251EISOLATED

RS-232Tx/Rx

Figure 8. System-level design.
http://www.analog.com/en/interface/digital-isolators/adum5401/products/product.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/analog-microcontrollers/aduc7027/products/product.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/power-management/linear-regulators/adp3339/products/product.htmlhttp://www.analog.com/en/interface/rs-232/adm3251e/products/product.htmlhttp://www.ni.com/labviewhttp://www.ni.com/labviewhttp://www.analog.com/en/interface/rs-232/adm3251e/products/product.htmlhttp://www.analog.com/en/power-management/linear-regulators/adp3339/products/product.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/analog-microcontrollers/aduc7027/products/product.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/adum5401/products/product.html



TheADC Confgure screen, shown in Figure 10, is used to set the

ADC channel, update rate, and PGA gain; to enable or disable

excitation currents; and or other general-purpose ADC settings.

Each ADC channel is calibrated by connecting the corresponding

DAC output channel to the ADC input terminal and adjusting

each range. When using this method o calibration, thereore,

the oset and gain errors o the AD5422 dictate the oset and

gain o each channel. I these provide insufcient accuracy,

ultrahigh-precision current and voltage sources can be used or

calibration i desired.

Figure 10. ADC Confgure screen.

Ater selecting the ADCs input channel, input range, and update

rate, we can now use theADC Stats screen, shown in Figure 11,

to display some measured data. On this screen, the user chooses

the number o data points to record; the sotware generates a

histogram o the selected channel, calculates the peak-to-peak

and rms noise, and displays the results. In the measurement

shown here, the input is connected through the AD8220 to

the AD7793: gain = 1, update rate = 16.7 Hz, number o

sample s = 512, input range = 10 V, input voltage = 2.5 V. The

peak-to-peak resolution is 18.2 bits.

Figure 11. ADC Stats screen.

In Figure 12, the input is connected directly to the AD7793,

bypassing the AD8220. The on-chip 2.5-V reerence is connected

directly to the AIN+ and AIN channels o the AD7793, providing

a 0-V dierential signal to the ADC. The peak-to-peak resolution

is 20.0 bits. I the ADC conditions remain the same but the

2.5-V input is connected through the AD8220, the peak-to-peak

resolution degrades to 18.9 bits or two reasons: at low gains, the

AD8220 contributes some noise to the system; and the scaling

resistors that provide the input attenuation result in some range

loss to the ADC. The PLC evaluation system allows the user to

change the scaling resistors to optimize the ADCs ull-scale range

thereby improving the peak-to-peak resolution.

ADC SETUP:

UPDATE RATE = 4.17HzGAIN = 1INPUT = 0V(2.5V COMMON-MODE)

PERFORMANCE:PEAK-TO-PEAKRESOLUTION = 20 BITS

Figure 12. AD7793 perormance.

Power Supply Input Protection: The PLC evaluation system

uses best practices or electromagnetic compatibility (EMC)

A regulated dc supply (18 V to 36 V) is connected to the board

through a 2- or 3-wire interace. This supply must be protected

against aults and electromagnetic intererence (EMI). The

ollowing precautions, shown in Figure 13, were taken in the board

design to ensure that the PLC evaluation system will survive any

intererence that may be generated on the power ports.

FLOATINGGND

GND

+24V

P1

L11mH

L21mH

D1

R1PIEZO

R1PIEZO

PTC1

C1330F

C215nF

C315nF

C415nF

R3PIEZO

R4PIEZO

FLOATING_GND

GND

+24VDC

Figure 13. Power supply input protection.

Apiezoresistor,R1,isconnectedtogroundadjacenttothe

power input ports. During normal operation, the resistance

o R1 is very high (megohms), so the leakage current is very

low (microamperes). When an electr ic current surge (caused

by lightning, or example) is induced on the port, the piezo

resistor breaks down, and tiny voltage changes produce rapid

current changes. Within tens o nanoseconds, the resistance

o the piezo resistor drops dramatically. This low-resistance

path allows the unwanted energy surge to return to the input

thus protecting the IC circuitry. Three optional piezoresistor

(R2, R3, and R4) are also connected in the input path to

provide protection in cases when the PLC board is powered

using the 3-wire confguration. The piezoresistors typically

cost well under one U.S. dollar.

Apositivetemperaturecoefcientresistor,PTC1,isconnected

in series with the power input trace. The PTC1 resistance

appears very low during normal operation, with no impact to

the rest o the circuit. When the current exceeds the nominal

PTC1s temperature and resistance rapidly increase. Thi

high-resistance mode limits the current and protects the inpu

circuit. The resistance returns to its normal value when the

current ow decreases to the nominal limit.



Y capacitors C2, C3, and C4 suppress the common-mode

conductive EMI when the PLC board operates with a oating

ground. These saety capacitors require low resistance and

high voltage endurance. Designers must use Y capacitors that

have UL or CAS cer tifcation and comply with the regulatory

standard or insulation strength.

InductorsL1andL2lteroutthecommon-modeconducted

intererence coming in rom the power ports. Diode D1

protects the system rom reverse voltages. A general-purpose

silicon or Schottky diode speciying a low orward voltage at

the working current can be used.

Analog Input Protection: The PLC board can accommodate

both voltage and current inputs. Figure 14 shows the input

structure. Load resistor R5 is switched in or current mode.

Resistors R6 and R7 attenuate the input. Resistor R8 sets the gain

o the AD8220.

These analog input ports can be subjected to electric surge or

electrostatic discharge on the external terminal connections.

Transient voltage suppressors (TVSs) provide highly eective

protection against such discharges. When a high-energy transient

appears on the analog input, the TVS goes rom high impedance

to low impedance within a ew nanoseconds. It can absorb

thousands o watts o surge power and clamp the analog input

to a preset voltage, thus protecting precision components rombeing damaged by the surge. Its advantages include ast response

time, high transient power absorption, low leakage current, low

breakdown voltage error, and small package size.

Instrumentation amplifers are oten used to process the analog

input signal. These precision, low-noise components are sensitive

VIN OR IIN

J1

R625k

C60.22F/50V

C51nF

D2TVS

D3IN4148

D4-A

D4-B

R75.1k

U1AD8220ARMZ

R5250

S2

R851k

S1

ISO

ISO

ISO ISO

REF + 0.5V

REF

VDDISO

VDDISO

+IN

RG

RG

IN

+VS

VS

VOUT ADC1_IN1+

C240.1F

C2510F

Figure 14. Analog input protection.

AD7793BRUZU2

ISO

ISO ISO

VDDISO

C130.1F

C1410F

IOUT1

AIN1(+)

AIN1()

AIN2()

AIN2(+)

DOUTAVDD DVDDDIN

SCLK

CLK

REFIN()

REFIN(+)GNDIOUT2

CS

ADC1_DOUT

ADC1_DIN

ADC1_SCLK

ADC1_CLK

ADC1_CS

C90.1F

C8

1nF

C71nF

D5-D

TVS

D5-CTVS

R9100

R141k

R10100

J2

TC

C120.1F

C111nF

C101nF

D5-BTVS

D5-ATVS

R11100

R135.1k

R12100

J3

RTD

Figure 15. Analog input protection.

to intererence, so the current owing into the analog input should

be limited to less than a ew milliamperes. External Schottky

diodes generally protect the instrumentation amplifer. Even when

internal ESD protection diodes are provided, the use o external

diodes allows smaller limiting resistors and lower noise and oset

errors. Dual series Schottky barrier diodes D4-A and D4-B divert

the overcurrent to the power supply or ground.

When connecting external sensors, such as thermocouples (TCs)

or resistance temperature devices (RTDs), directly to the ADC,

similar protection is needed, as shown in Figure 15.

TwoquadTVSnetworks,D5-CandD5-D,areputinafterthe

J2 input pins to suppress transients coming rom the port.

C7,C8,C9,R9,andR10formtheRFattenuationlteraheadof

the ADC. The flter has three unctions: to remove as much RF

energy rom the input lines as possible, to preserve the ac signal

balance between each line and ground, and to maintain a high

enough input impedance over the measurement bandwidth to

avoid loading the signal source. The 3-dB dierential-mode

and common-mode bandwidth o this flter are 7.9 kHz and

1.6 MHz, respectively. The RTD input channel to AIN2+ and

AIN2 is protected in the same manner.

Analog Output Protection: The PLC evaluation system can

be sotware-confgured to output analog voltages or currents in

various ranges. The output is provided by the AD5422 precision,low-cost, ully integrated, 16-bit digital-to-analog converter, which

oers a programmable current source and programmable voltage

output. The AD5422 voltage and current outputs may be directly

connected to the external loads, so they are susceptible to voltage

surges and EFT pulses.



Table 3. IEC Test Results

Test Item Description Result

EN and IEC 61000-4-2Electrostatic discharge (ESD) 4 kV VCD Max deviation 0.32% or CH3 Class B

Electrostatic discharge (ESD) 8 kV HCD Max deviation 0.28% or CH3 Class B

EN and IEC 61000-4-3

Radiated immunity 80 MHz to 1 GHz10 V/m, ver tical antenna polar ization Max deviation 0.09% or CH1, 0.30% or CH3 Class B

Radiated immunity 80 MHz to 1 GHz10 V/m, hor izonta l antenna polar ization Max dev iation 0.04% or CH1, 0.22% or CH3 Class B

Radiated immunity 1.4 GHz to 2 GHz3 V/m, vertical antenna polarization Max deviation 0.01% or CH1, 0.09% or CH3 Class B

Radiated immunity 1.4 GHz to 2 GHz3 V/m, hor izonta l antenna polari zat ion Max dev iation 0.01% or CH1, 0.09% or CH3 Class B

EN and IEC 61000-4- 4Electrically ast transient (EFT) 2 kV power port Max deviat ion 0.12% or CH3 Class B

Electrically ast transient (EFT) 1 kV signal port Max deviat ion 0.02% or CH3 Class A

EN and IEC 61000-4-5 Power line surge, 0.5 kV No board or part damage occurred, passed with Class B

EN and IEC 61000-4- 6

Conducted immunity test on power cord, 10 V/m or5 minutes Max deviation 0.09% or CH3 Class B

Conducted immunity test on input/output cable10 V/m or 5 minutes Max deviation 0.93% or CH3 Class B

EN and IEC 61000-4-8Magnetic immunity horizontal antenna polarization Max deviation 0.01% or CH3 Class A

Magnetic immunity vertical antenna polarization Max deviation 0.02% or CH3 Class A

ISO

+5VISO

ISO

C210.1F

C2010F

ISO

15VISO

ISO

C160.1F

C1510F

DVCC SEL

FAULT

DAC1_LATCH LATCH

DAC1_SCLK SCLK

DAC1_SDIN SDIN

DAC1_SDO SDO

CLR SEL

CLEAR

GND AGND RSET REFIN

REFOUT

+VSENSE

CCOMP2

VOUT

CCOMP1

VSENSE

IOUT

BOOST

DVCC AVSS AVDD

U3AD5422BREZ

R15

15k

C224nF

J5

VOLTAGE OUTPUT5V, 10V,0V TO 5V, 0V TO 10V, ETC.

D9-B

+15VISO

15VISO

D9-A

L3FERRITE

D11TVS

ISO

J6

CURRENT OUTPUT4mA TO 20mA,

0mA TO 20mA,0mA TO 24mA, ETC.

D10-B

+15VISO

15VISO

D10-A D12

TVS

ISO

Q1

ISO

ISOISO

ISO

C2322nF

R16

1k

R1710

ISO

+5VISO

ISO

C170.1F

C184.7F

D6 D7 D8TVS

ISO

J4

COMPLIANT VOLTAGEFROM EXT.12V TO 36V

C190.1F

Figure 16. Analog output protection.

The output structure is shown in Figure 16.

ATVS(D11)isusedtolterandsuppressanytransients

coming rom Port J5.

Anonconductiveceramicferritebead(L3)isconnectedin

series with the output path to add isolation and decoupling

rom high-requency transient noises. At low requencies

(



Authors

Colm Slattery [[email protected]]

graduated rom the University o Limerick with

a bachelors degree in engineering. In 1998, he

joined Analog Devices as a test engineer in the

DAC group. Colm spent three years working

or ADI in China and is currently working as an

applications engineer in the Precision Converters

group in Limerick, Ireland.

Derrick Hartmann [[email protected]]is an applications engineer in the DAC group at

Analog Devices in Limerick, Ireland. Derrick

joined ADI in 2008 ater graduating with a

bachelors degree in engineering rom the

University o Limerick.

Li Ke [[email protected]] joined Analog Devices

in 2007 as an applications engineer with the

Precision Converters product line, located in

Shanghai, China. Previously, he spent our years

as an R&D engineer with the Chemical Analysis

group at Agilent Technologies. Li received a

masters degree in biomedical engineer ing in 2003

and a bachelors degree in electr ic engineeri ng in 1999, bothrom Xian Jiaotong University. He has been a proessional

member o the Chinese Institute o Electronics since 2005.

Reerences1http://en.wikipedia.org/wiki/Programmable_logic_controller.2http://en.wikipedia.org/wiki/Distributed_control_system.3www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/ca.html.

4Inormation on all ADI components can be ound atwww.analog.com.

5www.analog.com/en/interace/digital-isolators/products/CU_over_iCoupler_Digital_Isolation/ca.html.

6

www.analog.com/en/interace/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/ca.html.

7www.analog.com/en/analog-microcontrollers/products/index.html .8www.ni.com/labview.

0.9980

0.9973

0.9974

0.9975

0.9976

0.9977

0.9978

0.9979

0 1400012000100008000600040002000

VOLTAGE

READING(

V)

DATA POINT

Figure 17. DAC channel dc voltage output. Radiated

immunity 80 MHz to 1 GHz @ 10 V/mH.

0.99795

0.99790

0.99785

0.99780

0.99775

0.99770

0.99765

0 45004000350030002500200015001000500

VOLTAGE

READING(

V)

DATA POINT

Figure 18. DAC channel 1 dc voltage output. Radiated

immunity 1.4 GHz to 2 GHz @ 3 V/mH.

Typical System Confguration: Figure 19 shows a photo o the

evaluation system and how a typical system might be confgured.

The input channels can readily accept both loop-powered and

nonloop-powered sensor inputs, as well as the standard industrialcurrent and voltage inputs. The complete design uses Analog

Devices converters, isolation technology, processors, and power-

management products, allowing customers to easily evaluate the

whole signal chain.

LOOP-POWEREDTRANSMITTER

GAS DETECTOR

4mA TO 20mA

0V TO 10V

INPUT TYPES ACCEPTEDRTD/TC,0V TO 5V, 0V TO 10V, 5V 10V4mA TO 20mA, 0mA TO 20mA

OUTPUTSRTD/TC,

0V TO 5V, 0V TO 10V,5V 10V4mA TO 20mA,0mA TO 20mA

PLC DEMO SYSTEM

Figure 19. Industrial control evaluation system.
mailto:[email protected]:[email protected]:[email protected]://en.wikipedia.org/wiki/Programmable_logic_controllerhttp://en.wikipedia.org/wiki/Distributed_control_systemhttp://en.wikipedia.org/wiki/Distributed_control_systemhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/http://www.analog.com/en/interface/digital-isolators/products/CU_over_iCoupler_Digital_Isolation/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/CU_over_iCoupler_Digital_Isolation/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/CU_over_iCoupler_Digital_Isolation/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.ni.com/labviewhttp://www.ni.com/labviewhttp://www.ni.com/labviewhttp://www.analog.com/en/analog-microcontrollers/products/index.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/overview/CU_over_isoPower_Isolated_dc-to-dc_Power/resources/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/CU_over_iCoupler_Digital_Isolation/fca.htmlhttp://www.analog.com/en/interface/digital-isolators/products/CU_over_iCoupler_Digital_Isolation/fca.htmlhttp://www.analog.com/http://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://www.analog.com/en/digital-to-analog-converters/products/evaluation-boardstools/CU_eb_PLC_DEMO_SYSTEM/resources/fca.htmlhttp://en.wikipedia.org/wiki/Distributed_control_systemhttp://en.wikipedia.org/wiki/Programmable_logic_controllermailto:[email protected]:[email protected]:[email protected]



Skin Impedance AnalysisAids Active and PassiveTransdermal DeliveryBy Liam Riordan

Drug delivery is one o the astest growing areas in the

pharmaceutical industry, with leading frms actively developing

alternatives to injections. Options such as oral, topical, pulmonary

(inhaler type), nanotechnology enabled, and transdermal drug

delivery systems are all current research areas. Transdermal

methods, which eature noninvasive delivery o medication through

the patients skin, overcome the skins protective barr ier in one o

two ways: passive absorption or active penetration.

The transdermal patch is one o the most common methods o

passive drug delivery. Applied to a patients skin, it saely and

comortably delivers a defned dose o medication over a controlled

period o time. The drug is absorbed through the skin into the

bloodstream. The nicotine patch is a prime example, but other

common uses include motion sickness, hormone replacement

therapy, and birth control. Passive delivery has two major

disadvantages: the speed o drug absorption is dependent on theskin impedance, and only a limited number o drugs are capable

o diusing through the skins protective barrier at acceptable

rates. As a result, major investment has been undertaken on active

methods o transdermal drug delivery. Active methods include

using ultrasonic energy to speed up drug diusion, using RF

energy to create microchannels through the stratum corneum

(outer layer o the epidermis), and iontophoresis.

Iontophoresis uses electrical charge to actively transport a drug

through the skin into the bloodstream. The device consists o two

chambers that contain charged drug molecules. The positively

charged anode will repel a positively charged chemical, while

the negatively charged cathode will repel a negatively charged

chemical. The electromagnetic feld developed between the two

chambers actively propagates the medicine through the skin in a

controlled manner.

Skin impedance is a key variable or transdermal delivery. The

complex impedance, which depends on age, race, weight, activity

level, and other actors, is requency dependent and difcul

to model. Dynamic measurement o skin impedance oers an

accurate and practical solution or optimal drug delivery.

+

POWER

SUPPLY

+

SKIN

EM

FIELD

VE CHAMBER

+VE CHAMBER

Figure 1. Iontophoresis.

Impedance spectroscopy acilitates accurate analysis o complex

impedances such as human skin, leveraging the act tha

resistor, capacitor, and inductor impedances vary dierently

with requency. As requency increases, a resistors impedance

remains constant; a capacitors impedance decreases; and an

inductors impedance increases. Exciting a test impedance with

a known ac waveorm makes it possible to determine the resistive

inductive, and capacitive components o the unknown impedance

Direct digital synthesizers1 (DDS) have exible phase, requency

and amplitude; sweep capability; and programmabilitymaking

them ideal or exciting unknown impedances. Embedded digita

signal processing and enhanced requency control allow the

devices to generate synthesized analog or digital requency-stepped

AD7476A

12-BIT SAR

ADC

LPF

AD8091

AD983x

AD593x

DDS

AD5161

AD5161

DFT CALCULATED

ON DSP

CONTROL INPUTS

UNKNOWN

IMPEDANCE

NETWORK

AD8091

Figure 2. Simple impedance analyzer.
mailto:liam.riordan%40analog.com?subject=http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/products/index.htmlhttp://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/products/index.htmlmailto:liam.riordan%40analog.com?subject=



waveorms. Figure 2 shows a block diagram o a simple impedance

analyzer. The ac waveorm generated by the AD98342 complete,

low-power, 75-MHz DDS is fltered, buered, and scaled by

the AD8091 high-speed, rail-to-rail op-amp. Another AD80913

buers the response signal and scales it to match the input range

o the AD7476A4 12-bit, 1-MSPS, successive-approximation

ADC.

This simple signal chain masks some underlying challenges,

however. First, the ADC must synchronously sample the excitation

and response waveorms over requency so that phase inormation

can be maintained. Optimizing this process is key to overallperormance. In addition, numerous discrete components are

involved, so varying tolerances, temperature dri t, and noise will

degrade measurement accuracy, particularly when working with

small signals.

The AD59335 12-bit, 1-MSPS integrated impedance converter

network analyzer overcomes these limitations by combining the

DDS waveorm generator and the SAR ADC on a single-chip, as

shown in Figure 3.

The AD5933 has an output impedance o a ew hundred ohms,

depending on the output range. This impedance could swamp the

unknown impedance, so an AD85316 op amp buers the signal,

as shown in Figure 4. Note that the receive side o the AD5933 isinternally biased to VDD/2, so this same voltage must be applied

to the noninverting terminal o the external amplifer to prevent

saturation. For saety, all excitation voltages and currents need

to be signal conditioned, attenuated, and fltered beore they are

applied to human tissue.

ROUT R2

R1

VOUT

DDS

TRANSMIT SIDEOUTPUT AMPLIFIER

2V p-p

VDD

20k

20k 1F

VDD/2

AD8531AD820AD8641AD8627

I-VPGA

RFB

RFB

VDD/2

VIN ZUNKNOWN

Figure 4. Low-impedance measurement confguration.

Reerences

1www.analog.com/en/rf-components/direct-digital-synthesis-

dds/products/index.html.2www.analog.com/en/rf-components/direct-digital-synthesis-

dds/ad9834/products/product.html.3www.analog.com/en/audiovideo-products/video-

ampsbuersflters/ad8091/products/product.html.4 www.analog.com/en/analog-to-digital-converters/ad-converters/

ad7476a/products/product.html .5www.analog.com/en/rf-components/direct-digital-synthesis-

dds/ad5933/products/product.html.6www.analog.com/en/audiovideo-products/display-driver-

electronics/ad8531/products/product.html.

VDD/2

DAC

Z()

SCL

SDA

DVDDAVDDMCLK

AGND DGND

ROUT VOUT

AD5933

RFB

VIN

1024-POINT DFT

I2C

INTERFACE

IMAGINARY

REGISTER

REAL

REGISTER

OSCILLATOR

DDS

CORE

(27 BITS)

TEMPERATURE

SENSOR

ADC

(12 BITS)LPF

GAIN

Figure 3. AD5933 functional block diagram.
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AccelerometersFantasy and RealityBy Harvey Weinberg

As applications engineers supporting ADIs compact, low-cost,

gravity-sensitive iMEMS accelerometers,1 we get to hear lots

o creative ideas about how to employ accelerometers in useul

ways, but sometimes the suggestions violate physical laws! Weve

rated some o these ideas on an inormal scale, rom real to dreamland:

Real A real application that actually works today and is

currently in production.

Fantasy An application that could be possible i we had

much better technology.

Dream Land Any practical implementation we can think

o would violate physical laws.

Washing Machine Load Balancing. Unbalanced loads during

the high-speed spin-cycle cause washing machines to shake

and, i unrestrained, they can even walk across the oor. An

accelerometer senses acceleration during the spin cycle. I an

imbalance is present, the washing machine2 redistributes the load

by jogging the drum back and orth until the load is balanced.Real. With better load balance, aster spin rates can be used to

wring more water out o clothing, making the dry ing process more

energy efcienta good thing these days! As an added beneft,

ewer mechanical components are required or damping the drum

motion, making the overall system lighter and less expensive.

Correctly implemented, transmission and bearing service lie is

extended because o lower peak loads present on the motor. This

application is in production.

Machine Health Monitors. Many industries change or overhaul

mechanical equipment using a calendar-based preventive

maintenance schedule. This is especially true in applications

where one cannot tolerate unscheduled downtime. So, machinery

with plenty o service lie let is oten prematurely rebuilt at a

cost o millions o dollars across many industries. By embedding

accelerometers in bearings or other rotating equipment, service lie

can be extended without risking sudden ailure. The accelerometer

senses the vibration o bearings or other rotating equipment to

determine their condition.

Real. Using the vibration3 signature o bearings to determine

their condition is a well proven and industry-accepted method

o equipment maintenance, but wide measurement bandwidth is

needed or accurate results. Beore the release o the ADXL001,4

the cost o accelerometers and associated signal conditioning

equipment had been too high. Now, its wide bandwidth (22 kHz)

and internal signal conditioning make the ADXL001 ideal or

low-cost bearing maintenance.

Automatic Leveling. Accelerometers measure the absoluteinclination o an object, such as a large machine or a mobile home.

A microcontroller uses the tilt inormation to automatically level

the object.

Real to Fantasy (depending on the application). Sel-leveling is

a very demanding application, as absolute precision is required

Surace micromachined accelerometers have impressive resolution

but absolute tilt measurement with high accuracy (better than

1 o inclination) requires temperature stability and hysteresis

perormance that todays surace-micromachined accelerometer

cannot achieve. In applications where the temperature range i

modest, high stability accelerometers like the ADXL2035 are

up to the task. Applications needing absolute accuracy to within

5 over a wide temperature range can be handled as well

However, more precise leveling over a wide temperature rangerequires external temperature compensation. Even with externa

temperature compensation absolute accuracy o better than 0.5o inclination is difcult to achieve. Some applications are currently

in production.

Human Interace or Mobile Phones. The acceleromete

allows the microcontroller to recognize user gestures, enabling

one-handed control o mobile devices.

Real.Mobile phone6 screens eat up most o the available real estate

or controls. Using an accelerometer or user interace unction

allows mobile phone makers to add buttonless eatures such as

Tap/Double Tap (emulating a mouse click/double click), screen

rotation, tilt controlled scrolling, and ringer control based on

orientationto name just a ew. In addition, mobile phone makers

can use the accelerometer to improve accuracy and usability

o navigation unctions and or other new applications. This

application is currently in production.

Car Alarm. The accelerometer senses i a car is jacked up or

being picked up by a tow truck and sets o the alarm.

Real. One o the most popular methods o auto thet is to stea

the car by simply towing it away. Conventional car alarms7 do no

protect against this. Shock sensors cannot measure changes in

inclination, and ignition-disabling systems are ineectual. This

application takes advantage o the high-resolution capabilities

o the ADXL2138. I the accelerometer measures an inclination

change o more than 0.5 per minute, the alarm is sounded

hopeully scaring o the would-be thie. Good temperature

stability is needed as no one wants their car alarm to go o becauseo changes in the weather, making the high ly stable ADXL213 an

ideal choice. This application is currently in production in OEM

and ater-market automotive anti-thet systems.

Ski Bindings. The accelerometer measures the total shock energy

and signature to determine i the binding should release.

Fantasy. Mechanical ski bindings are highly evolved, but limited

in perormance. Measuring the actual shock experienced by the

skier would accurately determine i a binding should release

Intelligent systems could take each individuals capability

and physiology into account. This is a practical accelerometer

application, but current battery technology makes it impractical

Small, lightweight batteries that perorm well at low temperature

will eventually enable this application.Personal Navigation. In this application, position is determined

by dead reckoning (double integration o acceleration over time to

determine actual position).
mailto:harvey.weinberg%40analog.com?subject=http://www.analog.com/en/mems/products/index.htmlhttp://www.analog.com/en/mems/products/index.htmlhttp://www.analog.com/en/mems/products/index.htmlhttp://www.analog.com/en/mems/products/index.htmlhttp://www.analog.com/en/industrial-solutions/white-goods/applications/index.htmlhttp://www.analog.com/en/industrial-solutions/vibration-analysis/applications/index.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl001/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl203/products/product.htmlhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/static/imported-files/application_notes/50324364571097434954321528495730car_app.pdfhttp://www.analog.com/en/sensors/inertial-sensors/adxl213/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl213/products/product.htmlhttp://www.analog.com/static/imported-files/application_notes/50324364571097434954321528495730car_app.pdfhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl203/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl001/products/product.htmlhttp://www.analog.com/en/industrial-solutions/vibration-analysis/applications/index.htmlhttp://www.analog.com/en/industrial-solutions/white-goods/applications/index.htmlhttp://www.analog.com/en/mems/products/index.htmlmailto:harvey.weinberg%40analog.com?subject=



Dream Land. Long-term integration results in a large error due

to the accumulation o small errors in measured acceleration.

Double integration compounds the errors (t2). Without some way

o resetting the actual position rom time to time, huge errors

result. This is analogous to building an integrator by simply

putting a capacitor across an op amp. Even i an accelerometers

accuracy could be improved by ten or one hundred times over what

is currently available, huge errors would still eventually result.

They would just take longer to happen.

Accelerometers can be used with a GPS navigation system9 when

the GPS signals are briey unavailable. Short integration periods(a minute or so) can give satisactory results, and clever algorithms

can oer good accuracy using alternative approaches. When

walking, or example, the body moves up and down with each step.

Accelerometers can be used to make very accurate pedometers that

can measure walking distance to within 1%.

Subwooer Servo Control. An accelerometer mounted on the

cone o the subwooer provides positional eedback to servo out

distortion.

Real. Several active subwooers with servo control are on the

market today. Servo control can greatly reduce harmonic distortion

and power compression. Servo control can also electronically

lower the Q o the speaker/enclosure system, enabling the use

o smaller enclosures, as described in Loudspeaker DistortionReduction.10 The ADXL19311 is small and light; its mass, added to

that o the loudspeaker cone, does not change the overall acoustic

characteristics signifcantly.

Neuromuscular Stimulator. This applicat ion helps people who

have lost control o their lower leg muscles to walk by stimulating

muscles at the appropriate time.

Real. When walking, the oreoot is normally raised when moving

the leg orward, and then lowered when pushing the leg backward.

The accelerometer is worn somewhere on the lower leg or oot,

where it senses the position o the leg. The appropr iate muscles are

then electronically stimulated to ex the oot as required.

This is a classic example o how micromachined accelerometers

have made a product easible. Earlier models used a liquid tiltsensor or a moving ball bearing (acting as a switch) to determine

the leg position. Liquid tilt sensors had problems because o

sloshing o the liquid, so only slow walking was possible. Ball-

bearing switches were easily conused when walking on hills. An

accelerometer measures the di erential between leg back and leg

orward, so hills do not ool the system and no liquid slosh problem

exists. The low power consumption o the accelerometer allows the

system to work with a small lithium battery, making the overall

package unobtrusive. This application is in production.

Car-Noise Cancellation. The accelerometer senses low-

requency vibration in the passenger compartment; the noise-

cancellation system nulls it out using the speakers in the stereo

system.

Dream Land. While the accelerometer has no trouble picking

up the v ibration in the passenger compartment, noise cancellation

is highly phase dependent. While we can cancel the noise at

one location (around the head o the driver, or example), it will

probably increase at other locations.

Conclusion

Because o their high sensitivity, small size, low cost, rugged

packaging, and ability to measure both static and dynamic

acceleration orces, surace micromachined accelerometers

have made numerous new applications possible. Many o

them were not anticipated because they were not thought

o as classic accelerometer applications. The imagination o

designers now seems to be the limiting actor in the scope o

potential applicationsbut sometimes designers can become too

imaginative! While perormance improvements continue to enable

more applications, its wise to try to stay away rom solutions

that violate the laws o physics.

Reerences1www.analog.com/en/sensors/inertial-sensors/adxl193/products/

product.html.2 www.analog.com/en/industrial-solutions/white-goods/

applications/index.html.3www.analog.com/en/industrial.4www.analog.com/en/sensors/inertial-sensors/adxl001/products/

product.html.5www.analog.com/en/sensors/inertial-sensors/adxl203/products/

product.html.6www.analog.com/en/wireless-solutions/eaturephonesmartphone/

applications/index.html.7www.analog.com/static/imported-fles/application_notes/50324

364571097434954321528495730car_app.pd.8www.analog.com/en/sensors/inertial-sensors/adxl213/products/

product.html.9 www.analog.com/en/automotive-solutions/navigation/

applications/index.html.10Greiner, Richard A. and Travis M. Sims, Jr. Loudspeaker

Distortion Reduction. JAES Vol. 32, No. 12. www.aes.org/e-lib/

browse.cm?elib=4467.11www.analog.com/en/sensors/inertial-sensors/adxl193/products/

product.html.
http://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.analog.com/en/industrial-solutions/white-goods/applications/index.htmlhttp://www.analog.com/en/industrial-solutions/white-goods/applications/index.htmlhttp://www.analog.com/en/industrialhttp://www.analog.com/en/sensors/inertial-sensors/adxl001/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl001/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl203/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl203/products/product.htmlhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/static/imported-files/application_notes/50324364571097434954321528495730car_app.pdfhttp://www.analog.com/static/imported-files/application_notes/50324364571097434954321528495730car_app.pdfhttp://www.analog.com/en/sensors/inertial-sensors/adxl213/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl213/products/product.htmlhttp://www.analog.com/en/automotive-solutions/navigation/applications/index.htmlhttp://www.analog.com/en/automotive-solutions/navigation/applications/index.htmlhttp://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://%20www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://%20www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://%20www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://%20www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://%20www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.analog.com/en/automotive-solutions/navigation/applications/index.htmlhttp://www.analog.com/en/automotive-solutions/navigation/applications/index.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl213/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl213/products/product.htmlhttp://www.analog.com/static/imported-files/application_notes/50324364571097434954321528495730car_app.pdfhttp://www.analog.com/static/imported-files/application_notes/50324364571097434954321528495730car_app.pdfhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/en/wireless-solutions/featurephonesmartphone/applications/index.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl203/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl203/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl001/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl001/products/product.htmlhttp://www.analog.com/en/industrialhttp://www.analog.com/en/industrial-solutions/white-goods/applications/index.htmlhttp://www.analog.com/en/industrial-solutions/white-goods/applications/index.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.htmlhttp://www.aes.org/e-lib/browse.cfm?elib=4467http://www.aes.org/e-lib/browse.cfm?elib=4467http://www.analog.com/en/sensors/inertial-sensors/adxl193/products/product.html



Digital Isolator SimplifesUSB Isolation in Medicaland Industrial ApplicationsBy Mark Cantrell

The personal computer (PC), currently the standard inormation-processing device or ofce and home use, communicates with most

peripherals using the universal serial bus (USB). Standardization,

cost, and the availability o sotware and development tools have

made the PC very attractive as a host-processor platorm or

medical and industrial applications, but the saety and reliability

requirements o these growing marketsespecially regarding

electrical isolationare very dierent rom the ofce environment

that has historically driven the design o the personal computer.

In the early days, personal computers were provided with serial and

parallel ports as standard interaces to the outside world. These

legacy standards had been inherited rom the earliest mainrame

computers. Another available communication standard, RS-232,

though slow, ft well into medical and industrial environments

because it allowed easy implementation o the required robustisolation. Its low speed and point-to-point nature were tolerated

because it was universally available and well supported.

USB, which has come to replace RS-232 as a standard port in

personal computers and their peripherals, has eatures that are ar

superior to the older serial port in nearly every respect. It has been

difcult and costly to provide the necessary isolation or medical

and industrial applications, however, so USB has been principally

used or diagnostic ports and temporary connections.

This article discusses various ways o applying isolation with USB.

In particular, a new option, the ADuM41601USB isolator, is now

available rom Analog Devices. This breakthrough product allows

simple, inexpensive isolation o peripheral devicesespecially

including the D+ and D linesincreasing the useulness o USBin medical and industrial applications.

About the Universal Serial Bus (USB)

USB is the serial interace o choice or the PC. Supported by

all common commercial operating systems, it enables on-the-y

connection o hardware and drivers. Up to 127 devices can exist

on the same hub-and-spoke-style network. Many data transer

modes handle everything rom large bulk data transers or

memory devices, to isochronous transers or streaming media,

to interrupt-driven transers or time-critical data such as mouse

movements. USB operates at three data transer rates: low speed

(1.5 Mbps),ull speed(12 Mbps), and high speed(480 Mbps). When

this system was created, consumer applications were emphasized;

connections had to be simple and robust, with controllers andphysical-layer signaling absorbing the complexity.

The USB physical layer consists o only our wires: two provide 5-V

power and ground to the peripheral device; the other two, D+ and

D, orm a twisted pair that can carr y dierential data (Figure 1).

These lines can also carry single-ended data, as well as idle states

that are implemented with passive resistors. When a device is

attached to the bus, currents in the passive resistor confguration

negotiate or speed, as well as establish a nondriven idle state. The

data is organized into data rames or packets. Each rame can

contain bits or clock synchronization, data type identifer, device

address, data payload, and an end-o-packet sequence.

PERIPHERAL

LOCAL

CONTROLLER

+SIE

LOCAL

CONTROLLER

+SIE

TRANSCEIVER

HOST

TRANSCEIVER

D+

D

3.3V

Figure 1. Standard elements o USB.

Control o this complex data structure is handled at each end

o the cable by a serial interace engine (SIE). This specialized

controlleror portion o a larger controller, which usually include

the USB transceiver hardwaretakes care o the USB protocol

During enumeration,2 when a peripheral is frst connected to the

cable, the SIE provides the host with the confguration inormation

and power requirements. During operation, the SIE ormats al

data according to the required transer type, as well as provides

error checking and automatic ault handling. The SIE handles al

ow o control on the bus, enabling and disabling the line drivers

and receivers as required. The hostinitiates all transactions, which

then ollow a well-defned sequence o data exchanges between hosand peripheral, including provisions or when data is corrupted and

other ault conditions. The SIE may be built into a microprocessor

so it may provide only the D+ and D lines to the peripheral

Isolating this bus presents several challenges:

1. Isolators are nearly always unidirectional devices, while the

D+ and D lines are bidirectional.

2. The SIE does not provide an external means to determine

data transmission direction.

3. Isolators must be compatible with the pull-up and pull-down

unctions o passive resistors, making them match across

the barrier.

Typical approaches to isolate the USB largely seek to sidestep the

above challenges.

A First Approach: Move the USB interace completely out o the

device that requires isolation (Figure 2). Many devices interace

generic serial buses to USB; an RS-232-to-USB interace is

shown in this example. The SIE provides a generic serial-interace

unction; isolation is implemented in the low-speed serial lines

This approach does not capitalize on the advantages o USB

however. All that has been created is a serial port that can be loaded

on-the-y. The interace IC could be customized through frmware

changes to identiy the peripheral, allowing a custom driver to

be created; but each peripheral would require a custom adaptor

Unless the adaptor was permanently afxed to the peripheral

it would be a servicing nightmare. In addition, the speed o the

interace would be limited to that o standard RS-232not clos

to the throughput o even low-speed USB.

Tx1

Tx2

Rx1

Rx2R

S-232

TRANSCEIVER

RS-232

TRANSCEIVER

5V5V ISO 5V 5V

ADuM1402

DC-TO-DC

Rx1

Rx2

Tx1

Tx2

3.3V

D+

D

USB TOUART

VBUS (5V)

D+

D

GND

Figure 2. Isolating through RS-232.
http://www.analog.com/en/press-release/5_20_09_ADI_Enables_Isolated_USB_Connections/press.htmlhttp://www.analog.com/en/press-release/5_20_09_ADI_Enables_Isolated_USB_Connections/press.htmlhttp://www.analog.com/en/press-release/5_20_09_ADI_Enables_Isolated_USB_Connections/press.htmlhttp://www.analog.com/en/press-release/5_20_09_ADI_Enables_Isolated_USB_Connections/press.htmlhttp://www.lvr.com/usbcenum.htmhttp://www.lvr.com/usbcenum.htmhttp://www.analog.com/en/press-release/5_20_09_ADI_Enables_Isolated_USB_Connections/press.html



A Second Approach: Use a standalone SIE that has an easily

isolated interace (Figure 3). Several products on the market use

ast unidirectional interaces, such as SPI, to connect an SIE to

a microprocessor. Digital isolators, such as the ADuM1401C

4-channel digital isolator, will allow ull isolation o an SPI bus.

The SIE contains buer memory that can be flled by the SPI

bus, so the operating speed o the SPI can be largely independent

o the speed o the USB. The SIE will negotiate with the USB

host or its highest possible connection speed and will dispense

data at the negotiated bus speed until it runs out o buered data.

The SIE will then tell the host to retry i more data is expected,allowing time or the SPI interace to refll the buers or another

transer cycle. Though very e ective, this scheme usually requires

modifcations to peripheral drivers, as well as bypassing existing

USB acilities built into the peripherals microprocessor. This

solution is expensive in terms o components and board space.

SPI

ADuM1401C

SYSTEMMICROPROCESSOR

SCLK

MOSI

SS

MISO

SCLK

MOSI

SS

MISO

USB CONTROLLERWITH TRANSCEIVER

VBUS (5V)

D

D+

GND

Figure 3. Isolated SIE through an SPI interace.

A Third Approach: I the microprocessors SIE uses an

external transceiver, the data and control lines to the transceiver

can be isolated (Figure 4). But USB requires as many as nine

unidirectional data lines between an SIE and its transceiver. This

represents a signifcant expense in high-speed digital isolators.

In addition, the astest available digital isolator works at about

150 Mbps. Though much aster than low- and ull-speed USB, it

cant handle high-speed data, limiting the speed range o the USB

interace. This solution is ully compatible with the USB drivers

provided or the microprocessors SIE, lowering development

costs, but the many isolation channels required make it expensiveto implement. Market trends toward increased integration will

obsolete this type o transceiver interace.

ADuM1402C

ADuM1401C


VP/VPO

VM/VMO

OE

PULL-UP

SUSPEND

RCV

USBTRANSCEIVER

VBUS (5V)

D

D+

GND

REG

3.3V

Figure 4. Isolated external USB transceiver.

A Fourth Approach: Insert the isolation directly into the D+ and

D lines (Figure 5). This allows D+/D isolation to be added to

existing USB applications without rewriting drivers or adding a

redundant SIE, a signifcant advantage over the other approaches.

Isolating the D+ and D lines complicates the situation, however,

as the device must be able to handle ow o control like an SIE,

as well as permit application o pull-up resistors and speed

determination across its isolation barr ier. It should also operate

without calling or the overhead o additional device drivers.

CONTROLLOGIC

CONTROLLOGIC

D+

D

D+

D


US

BS

IE

A

ND

TRAN

SCEIVER

US

BS

IE

A

ND

TRAN

SCEIVER

HOST

VISO (5V)VBUS (5V)

GND2GND1

Figure 5. Isolating the D+/D lines.

These challenges have been met with the ADuM4160USB isolator

(Figure 6), a new chip-scale device that supports direct isolation

o low- and ull-speed USB D+ and D lines.

1VBUS1

2GND1

3VDD1

7UD+

8GND1

4PRD_C

16 VBUS2

15 GND2

14 VDD2

11 DD

10 DD+

9 GND2

13 PIN

12 SPD5SPU

6UD

REG

PU LOGIC

REG

PU LOGIC

Figure 6. ADuM4160 block diagram.

Analog Devices iCoupler technology3 is particularly well-suited

to construction o a USB isolator. The primary challenges in

developi

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