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October 2014

Volume 24 Number 3

I N

T H I S

I S S U E

high step-down ratio

controller combines digital

power system management

with sub-milliohm DCR

sensing

Rugged IO-Link Solutions

Kevin Wrenner and Juan-G. Aranda

increase output voltage/

current with series-

connected isolated

µModule

converters

12V/100A Hot Swap™

design for server farm

compensate for wire drop

to a remote load

Industrial automation systems are growing more interconnected

and intelligent to accommodate demands for centralized control,

optimized production and reduced cost. IO-Link

is becoming

an increasingly popular interface to smart sensors and actuators,

combining signaling with power-over-cable technology. The interface

electronics must be rugged, power efficient and compact. Two

new parts capably meet these requirements. The LTC

2874 is a

highly integrated IO-Link master-side physical layer interface (PHY)

for four ports. The LT

3669 is a device-side PHY incorporating

a step-down regulator and LDO. To appreciate the numerous

features of these devices, it helps to review the requirements

of IO-Link. This article begins with a brief overview of IO-Link

technology, and follows with LTC2874

and LT3669 functions and features.

IO-LINK: POWER AND COMMUNICATION FOR

SMART DEVICES

Combining a power feed and a data link inside a cable

assembly isn’t new

but its presence in the world of indus-

trial automation is. IO-Link

emerged in 2009 as a com-

munication interface between automation control systems

(masters) and intelligent sensors and actuators (devices). In

3 it evolved into an international standard for program-

mable controllers

IEC 6

-9 single-drop digital commu-

nication interface for small sensors and actuators (SDCI)

whose purpose “extends the traditional digital input and

digital output interfaces as defined in IEC 6

-2 towards

a point-to-point communication link [enabling] the trans-

fer of parameters to Devices and the delivery of diagnostic

The LTC3882 POL controller with built-in digital power system management

(see page 16)

(continued on page 4)

w w w. li n e ar.co m

In this issue...

COVER STORY

Rugged IO-Link Solutions

Kevin Wrenner and Juan-G. Aranda

Linear in the News

LINEAR CELEBRATES TWO ANNIVERSARIES

DESIGN FEATURES

High Step-Down Ratio Controller Combines Digital

Power System Management with Sub-Milliohm DCR

Sensing and Accurate PolyPhase

Load Sharing

James A. McKenzie

In August

Linear celebrated the 25th anniversary of the opening of its

Singapore test facility

as well as the 20th anniversary of the company’s

Penang

Malaysia package assembly facility. These two facilities play an

important role in Linear’s vertically integrated manufacturing process. These

facilities help ensure seamless communication between wafer manufacturing

and packaging

enabling short and predictable product delivery times.

These state-of-the-art assembly and test operations complement

Linear’s two

-based wafer manufacturing operations in Camas

Washington and Milpitas

California. Such integrated operations

represent a major competitive advantage for customers.

Singapore Test Operation Reaches 25 Years

DESIGN IDEAS

What’s New with LTspice IV?

Gabino Alonso

Increasing Output Voltage and Current Range Using

Series-Connected Isolated µModule Converters

Jesus Rosales

12V/100A Hot Swap Design for Server Farms

Dan Eddleman

Compensate for Wire Drop to a Remote Load

Philip Karantzalis

Linear’s Singapore test operation

started in

989

has sophisticated capabili-

ties for high volume testing capabilities of the company’s numerous product

types—for both integrated circuits and µModule

products. The manufacturing

facility includes capability for high volume testing of many package types

tape

and reel

as well as pack and ship capability to customers and distributors. The

Singapore location also includes the Singapore Design Center

as well as the area

sales office supporting Singapore

Malaysia

India and Australia

New Zealand.

Over the years

Linear has continued to expand its Singapore test opera-

tions

with expansion of its first building in

997/

998 and a second

5-story building completed in 2005. A third major expansion is now

underway

planned for completion by the end of next year. With head-

count of nearly a thousand employees today

Linear has a highly experi-

enced team

capable of testing the most high performance analog IC

new product briefs

back page circuits

Linear’s Singapore test

facility reaches 25-year

milestone.

2 | October 2014 :

LT Journal of Analog Innovation

Linear in the news

Penang, Malaysia Package Assembly

Marks 20 Years

Started in

994

Linear’s package assembly

operation has over 20 years of experi-

ence with wafer sort and assembly for

a wide range of package types for both

and µModule products. Linear has

transformed its Penang assembly opera-

tion significantly over the years in several

phases

adding a second 6-story opera-

tions building to the prior facility. The

facility now assembles nearly 40 differ-

ent package types

as well as numerous

µModule products. The Penang facility

today employs over

500 people.

AWARDS

Best of Microwaves & RF Industry

Award

system bill-of-materials modifications. The

LTM4676 simplifies system characteriza-

tion

optimization and data mining during

prototyping

deployment and field opera-

tion. Target applications include optical

transport systems

datacom and telecom

switches and routers

industrial test

equipment

robotics

RAID and enterprise

systems where the cost of electrical utili-

ties

cooling and maintenance are critical.

EE Times China

also selected several other

Linear products as ACE Award finalists:

Power Semiconductor/ Voltage Converter

category:

LTC3300-

high efficiency

Electronica 2014, Messe München, Munich,

Germany, November 11-14, Hall A4, Booths 537 &

538—

Linear will exhibit its broad range

of analog products

with emphasis on

automotive and industrial applications.

Linear’s Joy Weiss will participate on

the

Markt & Technik

panel on “Energy

Efficient Semiconductors – How They

Will Change Our Lives – From Energy

Harvesting to IoT

Smart Production

Smart Buildings

Smart Grids and

Beyond” at 3:00 pm

November

More info at

www.electronica.de/

Energy Harvesting & Storage Conference, Santa

Clara Convention Center, Santa Clara, California,

November 19-20, Booth L28—

Presenting

bidirectional multicell battery balancer

RF/ Wireless/ Microwave category:

LTC555

300MH

to 3.5GH

ultra-high dynamic

range downconverting mixer

Data Conversion/ Driver/ Clock

category:

LTC2378-20 20-bit

sps

Microwaves & RF

magazine in June

presented Linear with the award for

Best Technical Support

as part of their

annual Best of Microwaves & RF Industry

Awards

highlighting “companies and

engineers that rise to the challenge and

provide cutting edge value to the industry.”

In presenting the award

the publication

cited Linear’s design support and technical

documentation

located conveniently on its

website. They highlighted the many design

support options offered by Linear

includ-

ing design simulations

quality and reli-

ability information

and technical support.

EE Times China ACE Awards

low power SAR ADC

CONFERENCES & EVENTS

Dust Consortium, Tokyo Conference Center

Shinagawa, Tokyo, Japan, October 17, 4F-402—

Linear’s energy harvesting and Dust

Networks

wireless sensor network

products. Presentations by Joy Weiss on

“Wireless Sensor Network Considerations

for the Industrial Internet of Things

(

)” and James Noon on “Energy

Harvesting: Battery Life Extension &

Storage.” More info at

www.idtechex.

com

energy-harvesting-usa

eh.asp

Second Annual Analog Guru’s Conference, Tokyo

Conference Center, Shinagawa, Tokyo, Japan,

December 5, 5F in the Large Hall—

Presentations

Presenting the newly established Dust

Consortium

a community of experts

in various industries focus on wireless

sensor networks

including press confer-

ence

study session and reception. More

info at

www.dust-consortium.jp/

by Linear Technology Co-founder and

Chief Technical Officer Bob Dobkin; Vice

President

Power Management Products

Steve Pietkiewicz; and Dr. A. Kawamoto.

More info at

http://analog-guru.jp/

Linear was recognized by

EE Times China

in September with the Product of the

Year Award in the Power Management

category for the LTM

4676. The device is

a dual

or single 26

µModule step-

down DC

DC regulator with a serial digital

interface. The interface enables system

designers and remote operators to com-

mand and supervise a system’s power

condition and consumption. The ability to

digitally change power supply parameters

reduces time-to-market and down time by

eliminating what would have historically

required physical hardware

circuit or

Linear was recognized

EE Times China

September with the

Product of the Year

Award in the Power

Management category

for the LTM4676, a

dual 13A or single 26A

µModule step-down

DC/DC regulator with a

serial digital interface.

October 2014 :

LT Journal of Analog Innovation

| 3

To solve the problems of inrush current control and fault isolation, the

LTC2874 generates L+ power supply outputs using a Hot Swap controller

and n-type power MOSFETs. The resistance of the power path is kept low

using external components for the MOSFETs and sense resistors, reducing

IC heat dissipation and maximizing power efficiency during operation.

(

LTC

2874/

3669, continued from page

)

MASTER

DEVICE

L+

information from the Devices to the

automation system.”

This technology

allows a distributed control system linked

by fieldbus networks to operate actuators

such as valve terminals; to operate

moni-

tor and collect data from sensors; and to

dynamically reconfigure their settings.

While IO-Link is fully described by a

protocol stack that includes data link and

application layers

it’s built upon physi-

cal layer interfaces

or PHY

(Figure

)

normally connected by 3-wire cables up to

20m long and terminated by standard M5

M8 or M

2 connectors. Two wires (L+ and

L−) supply 200

at 24

DC from master to

device

and a third wire is a point-to-point

half-duplex data line (CQ) that operates at

up to 230.4kb

s and shares the L− return.

Optionally

a fourth wire can serve as a

digital line. In specialized configura-

tions

this wire

along with a fifth

sup-

ply additional power for actuators.

Inherent to IO-Link systems is back-

ward compatibility. For example:

• IO-Link tolerates unshielded con-

nections

allowing reuse of standard

industrial wire in existing installations.

• IO-Link devices can operate without

an IO-Link master in a legacy digital

switching mode called Standard I

(SIO). Likewise

IO-Link masters can

operate legacy devices using SIO.

A built-in load current on the CQ line at

the master side (ILLM) facilitates opera-

tion of older sensors with discrete PNP-

type outputs

which only drive high.

Figure 1. IO-Link physical layer

interface (PHY). The device side

consists of a high side (and

optionally, low side) driver and a

receiver. The master side has a

push-pull driver, receiver, and a

current sink that operates as a

load for high side device outputs.

24V

DRV

C/Q

DRV

L–

Any overview of IO-Link must introduce

the scheme known as wake-up. Before

IO-Link communication can commence

IO-Link master must determine whether a

connected device is compatible

and

if it

identify the highest transmission rate

supported: 230.4kb

s (called COM3 mode)

38.4kb

s (COM2)

or 4.8kb

s (COM

). This

requirement

combined with another—an

IO-Link device must start up enabled to

operate in SIO mode outside of an IO-Link

system—poses a problem: how to gain

the attention of an IO-Link device that’s

dutifully transmitting its sensor output.

The answer is by shouting. The mas-

ter gains the attention of the device by

issuing a wake-up request (WURQ)

80µs

0.5

current pulse

which is guar-

anteed to exceed the drive strength of

an IO-Link device so that

upon detect-

ing the pulse

it may stop driving and

participate in a signaling exchange

of data that informs the master of its

maximum communication rate.

Once operating in communication mode

master and device exchange data asyn-

chronously in frames consisting of

bits

(Figure 2a). Most of these UART frames

are organized into larger units called

M-sequences (Figure 2b)

which begin

with a message sent by the master paired

with a reply message from the device.

M-SEQUENCE (MESSAGE SEQUENCE)

MASTER SEQUENCE

STOP BIT (SP)

START BIT (ST)

PARITY BIT (EVEN)

UART

FRAME

UART

FRAME

• • •

UART

FRAME

DEVICE MESSAGE

DATA OCTET

UART

FRAME

• • •

UART

FRAME

(a)

(b)

Figure 2. (a) IO-Link UART frames contain 11 bits of data. (b) Cyclic data is organized into paired exchanges of

UART frames between master and device called M-sequences.

4 | October 2014 :

LT Journal of Analog Innovation

design features

Two new interface parts target the first I/O technology

for communication with sensors and actuators to be

adopted as an international standard.

M-sequences transmit process data at

predetermined rates in various available

formats based on the type of device. Other

transmission modes support configuration

maintenance and diagnostic functions.

HOT SWAP CONTROLLER

PROTECTION AND ADVANTAGES

be disruptive or catastrophic

leading to

the question “is something burning?”

To solve the problems of inrush current

control and fault isolation

the LTC2874

generates L+ power supply outputs using

a Hot Swap controller and n-type power

MOSFET

. The resistance of the power path

is kept low using external components for

the MOSFET

and sense resistors

reduc-

ing IC heat dissipation and maximizing

power efficiency during operation. This

arrangement gives users flexibility in

MOSFET selection. Because this applica-

tion requires the MOSFET to operate in

linear mode during current limiting

older

planar process MOSFET

such as Fairchild’s

FQT7N

0 are recommended in order to

avoid damage-causing hot spots that

some newer versions and especially trench

transistors can develop in this mode.

The

controller provides SPI-operated on

off

control

current limiting

and a program-

mable

timed circuit breaker function.

The IO-Link standard has little to say

about the L+ power-over-cable supply

suggesting only that 200

and per-

haps a power switch are needed. But

potential problems abound when power

is connected to arbitrarily large loads.

Although high inrush current shouldn’t

damage the sturdy connectors used

for IO-Link

it can still cause connector

sparks and supply droop that can lead

to system resets. Although the power-

over-cable (POC) requirement of IO-Link

minimum) is modest compared to

alternative technologies such as Power

over Ethernet

anyone who has experi-

enced faults at 24

DC knows they can

The LTC2874 adds flexibility to inrush

current control by raising output sup-

plies in a controlled manner determined

either by current limiting (Figure 3a) or

for load independence

by an external

RC network (Figure 3b). When enabled

by a SPI register bit

the LTC2874 applies

foldback behavior to the current limit

in order to minimize power dissipation

in the MOSFET during start-up and over-

current conditions. An optional cable-

sensing mode keeps the L+ power disabled

until a cable is connected to the port.

Because IO-Link devices usually require

cable-supplied power to operate and

communicate

there’s normally no way

for them to notify their master that power

is absent. In such scenarios

master-side

diagnostic capabilities are especially

valuable. The LTC2874 reports changes

to output supply “power good” sta-

tus—along with a host of other condi-

tions including overtemperature

input

LOAD = 100µF

L+1

FLDBK_MODE = 1

L+2

L+3

10V/DIV

L+4

10V/DIV

= 22nF

= 10

LOAD = 10µF

L+1

L+2

L+3

L+4

L+

5V/DIV

FLDBK_MODE = 0

4ms/DIV

(a)

20ms/DIV

(b)

LT3669

OUT

2V/DIV

400µs/DIV

(c)

Figure 3. L+ power supply output start-up (a) in current limit, (b) defined by a GATE resistor-capacitor network, and (c) for LT3669 application circuit configured for 4V

buck output.

October 2014 :

LT Journal of Analog Innovation

| 5

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