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November 2015

Volume 25 Number 3

I N

T H I S

I S S U E

CAN bus transceivers

operate from 3.3V or 5V

and withstand ±60V faults

low power IQ modulator

for digital communications

Control Individual LEDs in Matrix

Headlights with Integrated 8-Switch

Flicker-Free Driver

Keith Szolusha

low profile supercapacitor

power backup with input

current limiting

boost 12V to 140V with a

single converter IC

LEDs combine design flexibility with practical, robust circuitry,

enabling automotive designers to produce striking headlight designs

matched by exceptionally long life and performance. Automobile

designers are increasingly incorporating LEDs in lighting because

they can be arranged in distinctive eye-catching designs—helping

distinguish new models from old, or high end from economy.

There is no question that automobile

LED

lighting has arrived, but it has not yet reached its full

potential. Future models will feature more

LED

lights, including new shapes and colors, and more

control over the individual

LED

. Simple strings of

LED

will give way to

matrices

LED

that can be individually

dimmed via computer control, enabling unlimited real-time

pattern control and animation. The future has arrived:

Linear Technology’s

3965 matrix

LED

driver makes it

easy to take the next step in automotive lighting design.

C CONTROL OF EIGHT POWER SWITCHES WITH A

SINGLE IC

A basic

LED

headlight design operates with uniform

LED

current

and thus

uniform brightness. But this leaves much

of the

LED

’ potential on the table. Matrix headlights take

advantage of the innate abilities of

LED

by enabling control

of the brightness of individual

LED

within

LED

strings.

It is not difficult, in theory, to address the individual

LED

a matrix via computer-controlled power switches, allowing

individual

LED

to be turned on or off, or

PWM

dimmed,

The LT3965: limitless control of automotive matrix headlights and lighting systems

(continued on page 4)

w w w. li n e ar.co m

In this issue...

COVER STORY

Control Individual LEDs in Matrix Headlights

with Integrated 8-Switch Flicker-Free Driver

Keith Szolusha

Linear in the News

LINEAR TECHNOLOGY CO-FOUNDERS RECEIVE

ACE LIFETIME ACHIEVEMENT AWARD

DESIGN FEATURES

CAN Bus Transceivers Operate from 3.3V

or 5V and Withstand ±60V Faults

Ciaran Brennan

Linear Technology co-founders Bob Swanson and Bob Dobkin received

UBM

Canon’s

EDN

and

EE Times

ACE

Lifetime Achievement Award

at a ceremony at the Embedded Systems Conference in Santa Clara,

California in July. The award is presented annually to individuals for

their contributions to the electronics industry, selected by a panel of

academic and business leaders, and editors of

EDN

and

EE Times.

Bob Swanson and Bob Dobkin founded Linear Technology 34 years

ago, with a goal of building unique high performance analog

The company now employs 4,865 people in over 50 locations world-

wide. Linear’s name has become synonymous with innovative, high

quality analog solutions in a broad range of application areas.

EDN

Senior Technical Editor Steve Taranovich stated, “Bob Swanson and

Bob Dobkin are unique as individuals in their decades-deep contributions

to integrated electronics, as well as their longevity in Silicon Valley. They

are also exceptional as a team because of their unprecedented continuity of

management at a semiconductor company, as well as their refreshing style of

management, amplifying Linear Technology’s engineering talent. For these

reasons and many more,

EE Times

and

EDN

chose to honor Bob Swanson

and Bob Dobkin with the 20

ACE

Lifetime Achievement Award.”

Steve Taranovich continued, “The talents and experiences of these two leaders,

in my estimation, have brought about a corporate culture unlike most of

the companies in the electronics business today. This culture encourages

innovation and strongly values and recognizes the company’s engineering

talent so that when a good idea emerges, management recognizes it and

‘gets out of the way’ to allow the engineer to bring it to fruition.”

The following comments are excerpted from the

EDN

interview

with Bob Swanson and Bob Dobkin:

www.linear.com/46876.

Bob Swanson:

“If you were an Analog Aficionado, Linear Technology looked

Low Power IQ Modulator for Digital Communications

Bruce Hemp and Sunny Hsiao

Low Profile Supercapacitor Power Backup

with Input Current Limiting

David Salerno

DESIGN IDEAS

What’s New with LTspice IV?

Gabino Alonso

Boost 12V to 140V with a Single Converter IC

Victor Khasiev

back page circuits

like a bunch of great technical guys just doing analog and they wanted to

be part of that. After 34 years, we are still the same. We can hire as many

good people as we can afford to hire. So the great thing we have going for

us is that we have a disproportionate share of really innovative people. We

leverage that because the world needs innovative analog solutions.”

2 | November 2015 :

LT Journal of Analog Innovation

Linear in the news

They are strong, talented and intelligent

leaders, but with a touch of humility and

compassion for their employees from

which other companies can learn a great

deal. The book entitled,

The Company

That No One Leaves

gives wonderful

insight into one of the key reasons this

company has had such success over the

last 34 years.”

www.linear.com/4675

Linear Technology co-founders

Bob Swanson and Bob Dobkin

received UBM Canon’s

EDN

and

EE Times

ACE Lifetime

Achievement Award at a

ceremony at the Embedded

Systems Conference.

AWARDS

• The

LTC

2983 digital temperature

measurement

received the

EDN

EE Times

Analog Ultimate

Product

ACE

Award.

• The LTC2000

6-bit, 2

sps

DAC

received the Best Product Award

from

EDN China

in the Analog

and Mixed Signal

category.

CONFERENCES & EVENTS

The Wireless Congress: Systems & Applications,

Konferenzzentrum, Munich, Germany, Nov. 17–18—

Bob Dobkin:

“One the things we do is

Bob Swanson:

“Smart, happy people

to hire engineers who want to inno-

vate and build products. And then we

don’t get in their way. So they build

products, they like what they are doing,

and that works well within Linear.”

Bob Dobkin:

“If you do some products right,

they will sell for over 30 years. If we do

some products as well as they can be

done, you never have to do them again.”

Bob Swanson:

“Obviously we have great

products, but competitors have great prod-

ucts too. In this analog-challenged world,

we have been so good at transferring our

knowledge to customers. I will occasion-

ally see the big customers at social events.

They always tell me how much they

depend upon our design and field people.

Our field people are brilliant

FAE

.”

Bob Swanson:

“One of the things that

probably can be innovators. I tell this

story—about five or six years ago some-

body asked Steve Jobs: ‘You guys are

acknowledged to be the best at

and

innovation, and you’ve got the smallest

budget.’ And he said, ‘All you need

is a handful of real innovators and you

can be successful. And I’ve got a handful

of really good innovators and that’s all I

need.’ So

is not an arms race.

is about having innovators. Going from

00 engineers to 200 does not automati-

cally double your innovation. If you have

25 innovators and you can get two or

three more a year, you’re in good shape.”

Bob Dobkin:

“One way we are unique is

Presenting energy harvesting and wire-

less sensor networks. Joy Weiss presents

“Low Power Wireless Sensor Networks

for IoT

”

www.wireless-congress.com

Energy Harvesting & Storage Conference,

Santa Clara Convention Center, Santa Clara,

California, Nov. 18–19, Booth N28—

Presenting

Bob Dobkin told me was that power

was analog. So take an automobile

with hundreds of processors—every

one of them needs a power supply.

And it is typically a power supply that

is way more difficult than it was 20

years ago. The challenge in this ‘explo-

sion of electronics’ in the automobile

seems to me to be as much about

solving analog issues as digital issues.”

that the engineering group comes up

with the product ideas. We don’t go

and do a marketing survey. Our engi-

neers visit customers and figure out

new products. We’re excited to work

on things that the customers want.”

Steve Taranovich concluded: “During

this interview with these two industry

icons, I sensed that they know their place

in the industry and in their company,

and effectively use the talent of their

employees in a way that I personally have

never seen in my 42 years in electronics.

energy harvesting and wireless sensor

networks. Ross Yu on “Low Power

Wireless Sensor Networks for IoT

”

;

Tony Armstrong on “Energy Harvesting:

Battery Life Extension & Storage.”

www.idtechex.com

energy-harvesting-usa

3rd Annual Analog Gurus Conference, Tokyo

Conference Center Shinagawa, Tokyo, Japan,

Nov. 18—

Linear’s analog gurus present.

CTO

Bob Dobkin on“Inside Precision

Voltage References,” Steve Pietkiewicz,

VP,

Power Management products on

“High Performance µModules

” and Bob

Reay,

VP,

Mixed Signal products on“High

Precision Temperature Measurement.”

November 2015 :

LT Journal of Analog Innovation

| 3

When combined with a suitable constant-current LED driver, the matrix dimmer LED

driver allows the individual LEDs to be computer-controlled in headlights, daytime

running lights, brake and tail lights, side-bending lights, and other trim lighting.

(

3965, continued from page

)

to create unique patterns and func-

tions. Each

LED

(or segment of

LED

)

requires either its own converter or its

own shunt power switch. It is possible

to build a matrix driver with traditional

driver

converter

that include a serial

communications feature, but once more

than two or three switches are needed

for a matrix of

LED

, designing a discrete

component solution becomes challeng-

ing, involving a matrix of components

that exceeds the size of the

LED

matrix.

The LT3965

8-switch matrix

LED

dimmer makes it easy to control large

or small

LED

matrices (up to 5

LED

Figure

shows the LT3965 in action on

Linear’s demonstration circuit

Its highly integrated design (Figure 2)

minimizes component count. The indi-

vidually addressable channels of the

LT3965 can be used to control

LED

matrices in many ways, including:

• Each LT3965 can control eight dimming

channels—eight

LED

or eight clus-

ters—within a string of

LED

• The eight channels can control the

individual red, green, blue and white

light on two

RGBW LED

modules for

adjustable brightness or changing

color of dashboard or trim lighting.

• Multiple LT3965s can be indi-

vidually addressed on a single

communications bus to multiply

the strings in a large array.

• The LT3965 can control multiple

LED

per channel, or channels can

be combined to efficiently control

a single

LED

at higher current.

When combined with a suitable constant-

current

LED

driver, the matrix dimmer

LED

driver allows the individual

LED

to be computer-controlled in head-

lights, daytime running lights, brake

and tail lights, side-bending lights,

dashboard display and other trim light-

ing. The LT3965’s built-in automatic

fault detection protects individual

LED

in case of a failure and reports

failures to the microcontroller.

The 60

LT3965 includes eight integrated

330

power switches, which can be

connected to one or more

LED

. The

power switches act as shunt devices

by turning off or

PWM

dimming the

LED

on a particular channel. The

switches create eight individually

controlled brightness channels (up to

256:

dimming ratio) and eight fault-

proof segments of an

LED

string.

The LT3965 can handle a string current

of 500

when all eight power switches

are on at the same time (all

LED

off).

The switches can be connected in paral-

lel and run at

through four channels

LED

as shown later in this article.

Regardless of the number of

LED

current, the

LED

string must be driven by

a properly designed converter that has the

bandwidth to handle the fast transients

of the matrix dimmer. Some reference

designs are included in this article.

LT3797 BOOST-THEN-DUAL-BUCK

MODE DRIVES TWO STRINGS, 16

LEDs AT 500mA WITH TWO LT3965s

The eight shunt power switches of the

LT3965

control the brightness of eight

channels of

LED

500

The string

voltage of the

LED

matrix dimmer

system can be between

and

26V

depending on how many

LED

are on or

off at a given time. The recommended

converter topology to drive these

LED

is a

30V

step-down converter with high

bandwidth and little or no output capaci-

tor. This step-down topology requires

that

9V–

automotive input is “pre-

boosted” to a

30V

rail from which the

step-down regulators can operate.

The triple output LT3797

LED

controller

conveniently serves as a single-

solution

for both the “pre-boost” and step-down

functions—it can be configured as a

step-up voltage regulator on one channel,

followed by step-down

LED

drivers on the

other two channels. Each of two step-

down

LED

drivers can drive a string of

matrix-dimmed

LED

. This topology has

a number of advantages, most notably,

regardless whether the

LED

string voltages

are above or below the battery voltage, the

circuit continues to function optimally.

Figure 3 shows the schematic of the

demonstration board shown in Figure

a boost-then-dual-buck mode LT3797 and

LT3965 matrix dimming headlight system

with

LED

at 500

Each

LED

can

be individually controlled to be on, off

PWM

dimmed down to

/256 bright-

ness. The 350

switching frequency of

the LT3797 is outside the

band (good

4 | November 2015 :

LT Journal of Analog Innovation

design features

Demonstration circuit DC2218 features a complete matrix LED dimmer system with

LT3797 boost-then-dual-buck mode LED drivers and two LT3965 matrix dimmers that

drive 16 LEDs at 500mA from a car battery. The board operates a matrix headlight

with an attached I

C microcontroller via DC2026, the Linduino One demo circuit.

12V 3A DC

POWER INPUT

BOARDS CAN BE EASILY CONNECTED IN SERIES,

ALL CONTROLLED BY A SINGLE µCONTROLLER

TWO 26V, 500mA SUPPLIES

PRODUCED BY A SINGLE LT3797

BOOST-THEN-DUAL-BUCK MODE

CONVERTER

TWO LT3965 MATRIX

DIMMERS PER BOARD

SYNC AT 350kHz

CONTROLLED BY LTC6900.

PWM AT 170Hz

POT ALLOWS

DIRECT PATTERN

INTERACTION

PREPROGRAMMED

LINDUINO DC2026

INCLUDED.

USB FOR µCONTROLLER

REPROGRAMMING AND

CONTOL VIA GUI

SELECT FROM SEVEN

PRELOADED DIMMING

PATTERNS OR GUI

CONTROL

16 HIGH POWER LEDs

(EIGHT LEDs FOR EACH

LT3965) MOUNTED ON BOARD

WITH PROTECTIVE FILTER.

CONNECTIONS FOR MORE LEDs

PROVIDED.

Photo:

Steven Tanghe

Figure 1. LT3965 LED matrix dimmer demonstration circuit DC2218 run as a Linduino™ shield (DC2026). This demonstration circuit runs headlight, turning light, tail light

and trim patterns and can be evaluated with Linear’s graphical user interface via a USB cable.

for

EMI)

and the resulting

PWM

dimming frequency of the LT3965, gener-

ated from the same 350

clock, is above

the visible range. With the system properly

synchronized, the LT3797 and LT3965

matrix headlight operates flicker-free.

The LT3797 buck mode converters are

optimized for extremely fast transients

with little or no output capacitor and

properly compensated control loops. These

>30

bandwidth converters tolerate fast

LED

transients as the

LED

are turned on

and off and

PWM

dimmed at will. A filter

capacitor placed on the

LED

sense resis-

tor replaces a pole in the control system

that is lost when the output capacitor is

reduced or removed for the fast transient

performance of the matrix dimmer.

November 2015 :

LT Journal of Analog Innovation

| 5

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