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February 2016

Volume 26 Number 1

I N

T H I S

I S S U E

low I

, 60V monolithic

boost/sepic/inverting

converter in ThinSOT or

3mm x 2mm DFN

The Evolution of High Voltage Digital

Power System Management

Hellmuth Witte

98% efficient buck-boost

LED driver with internal

PWM dimming and spread

spectrum

matrix LED dimmer enables

accurate color control in

RGBW LEDs

monolithic 3mm × 3mm,

17V, 2A step-down

regulator

The LTC 3886 takes inputs up to 60V and produces two 0.5V-to-

13.8V outputs—enabling it to easily drop into industrial, server

and automotive environments as an intermediate or point-of-load

(POL) supply. Other controllers with similarly impressive input/

output ranges cannot match the LTC3886’s digital management

capabilities. Its I

C-based PMBus-compliant serial interface allows

power supply designers to configure, monitor, control and expand

capabilities via PC-based, graphical LTpowerPlay and then store

optimal production settings in the LTC3886’s onboard EEPROM.

No board changes are required, since capabilities and optimization

settings (including compensation) can be changed via software.

This 2-channel PolyPhase

DC/DC

synchronous step-down

switching regulator controller employs a constant-frequency,

current-mode architecture, with accurate input and output

current sensing and programmable loop compensation,

and is available in a 52-lead (7mm × 8mm)

QFN

package.

Accurate voltage and current sensing, adjustable compensa-

tion and dedicated

PGOOD

pins make the LTC3886 ideal for

industrial applications that demand versatile power system

design, control, monitoring, programming and accuracy.

FLEXIBLE FEATURE SET

Figure

shows a generalized schematic of a LTC3886. The

to 750

PWM

switching frequency range, and

low

DS(ON)

integrated

-channel

MOSFET

gate drivers

support a plethora of external components and enable

power capability and system cost optimization. The

The LTC6811 ushers in Linear’s fourth generation of multicell battery stack monitors.

See page 2 for more about this powerful device.

(continued on page 4)

w w w. li n e ar.co m

In this issue...

COVER STORY

The Evolution of High Voltage Digital

Power System Management

Hellmuth Witte

Linear in the News

LINEAR TECHNOLOGY ANNOUNCES FOURTH GENERATION

AUTOMOTIVE BATTERY STACK MONITOR

DESIGN FEATURES

Low I

, 60V Monolithic Boost/Sepic/Inverting

Converter in ThinSOT or 3mm x 2mm DFN

Owen Jong

Electric and hybrid vehicles can require tens or hundreds of series-

connected battery cells, with battery stacks up to

000

or higher.

A battery management system in this high voltage environment

must be able to reject common mode voltage fluctuations so that it

can accurately monitor and control each cell in the strings.

High voltage battery stacks in vehicles face challenging operating condi-

tions, with significant electrical noise and wide operating temperatures.

Battery management electronics are expected to maximize operating range,

lifetime, safety and reliability, while minimizing cost, size and weight.

In November, Linear announced the LTC68

, Linear Technology’s latest

multicell battery stack monitor, incorporating an ultrastable voltage refer-

ence, high voltage multiplexers,

6-bit delta-sigma

ADC

, and a

bps isolated

serial interface. The LTC68

can measure up to

2 series-connected battery

cells at voltages with better than 0.04% accuracy. With eight programmable

third order lowpass filter settings, the LTC68

provides outstanding noise

reduction. In the fastest

ADC

mode, all cells can be measured within 290µs.

The LTC68

battery stack monitor was announced by Linear at press meetings

worldwide. Linear’s technical team presented the attributes of this advanced

automotive device and its contribution to improved efficiency, reliability

and safety in the next generation of electric and hybrid

electric vehicles.

For large battery packs, multiple LTC68

s can be interconnected and oper-

ated simultaneously, using Linear Technology’s proprietary 2-wire isoSPI

™

interface. This built-in interface provides electrically isolated, high

noise

immune communication for data rates up to

bps. Using twisted pair,

many LTC68

can be connected in a daisy chain to a single host processor,

enabling measurement of hundreds of cells in high voltage battery stacks.

The LTC68

is the fourth generation of Linear’s road-proven battery monitor

, designed to surpass the environmental, reliability and safety requirements

of automotive and industrial applications. The LTC68

is fully specified for

operation from −40°

25°

. It has been engineered for

ISO

26262 (

ASIL)

compliant systems, with extensive fault coverage via its redundant voltage

reference, logic test circuitry, cross-channel testing, open wire detection capa-

bility, a watchdog timer and packet error checking on the serial interface.

Buck-Boost LED Driver Reaches 98%

Efficiency, Features Internal PWM Dimming

and Spread Spectrum without Flicker

Keith Szolusha

DESIGN IDEAS

What’s New with LTspice IV?

Gabino Alonso

Matrix LED Dimmer Enables Accurate Color

Control and Pattern Production in RGBW LEDs

Keith Szolusha

High Efficiency 17V, 2A Synchronous Monolithic

Step-Down Regulator with Ultralow Quiescent Current

in a 3mm × 3mm DFN

Gina Le and Jian Li

back page circuits

2 | February 2016 :

LT Journal of Analog Innovation

Linear in the news

Safety and Reliability

CONFERENCES & EVENTS

CAR-ELE Japan, 8th International Automotive

Electronics Technology Expo, Tokyo, Japan,

January 13–15, Booth W8-13—

Presenting

The LTC68

enables high reliability, high

stability and high measurement accuracy

systems, built for years of operation in

environments of high voltages, extreme

temperatures, hot plugging and electrical

noise. The LTC68

supports automo-

tive functional safety, as defined by the

ISO

26262 standard, which systemati-

cally addresses potential hazards in an

automobile caused by the malfunction-

ing behavior of electronic and electrical

systems. This requires that the system

must continuously confirm the proper

operation of key electronics, such as the

cell voltage measurement electronics.

Accuracy

Linear’s automotive solutions, including

LED

lighting, collision avoidance and

improved audio.

www.car-ele.jp

Home/

European Advanced Automotive & Industrial

Battery Conference (AABC Europe 2016), Mainz,

Germany, January 25–28—

Presenting Linear’s

Linear CTO Bob Dobkin presents at the Third Annual

Analog Gurus Conference in Tokyo.

To achieve outstanding accuracy,

the LTC68

includes a dedicated

sub-surface Zener voltage reference,

offering outstanding long term stabil-

ity and accuracy, over time and oper-

ating conditions. This enables the

LTC68

to measure every battery cell

to within less than

of error.

Added Functionality

complex functions, such as multiplexers

for expanded analog inputs or

EEPROM

to store calibration information.

For more information, visit

www.linear.com

product

LTC68

THIRD ANNUAL ANALOG GURUS

CONFERENCE HELD IN TOKYO

battery management systems. Participating

in three technology-focused symposia

covering lithium-ion chemistry, lithium-

ion engineering and

capacitor devel-

opments, and an application-focused

symposia with two parallel tracks focusing

on high volume and industrial

specialty

automotive.

www.advancedautobat.

com

conferences

automotive-battery-

conference-Europe-20

6/index.html

Embedded World, Nuremberg, Germany, February

23–25, Booth 310, Hall 4A

—

Showcasing demos

On November

8, Linear held the Third

Annual Analog Gurus Conference in

Tokyo. Nearly 400 attendees heard presen-

tations from analog experts, including:

• Professor Akira Hyogo, Professor

Vice President Faculty of Science &

Technology, Tokyo University of Science

• Bob Dobkin, Co-Founder & Chief

Technical Officer, Linear Technology

• Steve Pietkiewicz, Vice President

Power Management Products,

Linear Technology

• Bob Reay, Vice President, Mixed

Signal Products, Linear Technology

Conference attendees received signed

copies of the just published Japanese

edition of

Analog Circuit Design, Volume

2, Immersion in the Black Art of Analog

Design, Part 1—Power Management,

edited by Bob Dobkin and Jim Williams.

The LTC68

is designed to operate at the

most critical location in the battery system:

directly connected to the battery cells. The

LTC68

can monitor battery current and

temperature sensors, and closely correlate

these values to cell measurements.

The LTC68

offers very flexible general

purpose

that can operate as digital

inputs, digital outputs or as analog inputs.

When operated as analog inputs, the

LTC68

can measure any voltage from

–

to 5

with the same measurement

accuracy as the cell measurements. The

LTC68

allows cell measurements to be

synchronized with these external signals or

with the

2-cell stack voltage. The LTC68

has built-in capability, through the digital

I/O,

to control

SPI

slave devices.

This enables the LTC68

to control more

of Linear’s latest products and solu-

tions, focusing on electronic systems,

distributed intelligence, the Internet

of Things, e-mobility and energy effi-

ciency.

www.embedded-world.de

WEKA Batterie Forum, Munich, Germany,

March 9–10—

Presenting Linear’s battery

management system products with live

demos.

www.elektroniknet.de

term

ine/?schid=

0260&date=20

603

Power Supply Anwenderforum, Munich,

Germany, March 9–10—

Presenting Linear’s

µModule

portfolio and showcasing

live demos.

www.elektroniknet.de

term

ine/?schid=

0260&date=20

603

APEC 2016, Long Beach Convention Center,

Long Beach, CA, March 20–24, Booth 1233—

Showcasing Linear’s broad line of

high performance power management

products.

www.apec-conf.org/

February 2016 :

LT Journal of Analog Innovation

| 3

The LTC3886’s regulation and supervision accuracy

reduces total system costs with fewer output

capacitors, while still meeting the tight input

voltage requirements of downstream ICs.

(

LTC

3886, continued from page

)

LTC3886 can readily accommodate a

wide variety of industrial, medical, and

point-of-load applications due to a

flexible programmable feature set that

addresses the specific application at hand.

ADAPTABILITY THROUGH

PROGRAMMABILITY

• Fault response and fault propagation via

the

FAULT

pins

• Device address

Switching frequency, device phasing

and output voltage are also program-

mable with external configuration

resistors. In addition, all

28 possible

addresses are resistor selectable.

POWER GOOD, SEQUENCING AND

PROGRAMMABLE FAULT RESPONSE

The following parameters of the

LTC3886 are configurable and

storable in the onboard

EEPROM

via the

C/SMB

interface:

• Output voltage, overvoltage,

undervoltage and overcurrent limit

• Input

ON/OFF

voltage, input overvoltage

and input overcurrent warning

• Digital soft-start

stop, sequencing,

margining

• Control loop compensation

•

PWM

switching frequency and phasing

The dedicated

PGOOD

pin for each

channel simplifies enabling event-based

sequencing across multiple LTC3886s and

other power system management

. The

LTC3886 also supports time-based sequenc-

ing. After waiting the

TON_DELAY

amount

of time following the

RUN

pin going high,

PMB

command to turn on, or the

pin voltage rising above a preprogrammed

voltage, the outputs are enabled.

Time-based power off sequencing is

handled in a similar way. To assure proper

time based sequencing, simply connect all

SHARE_CLK

pins together and connect

together the

RUN

pins of all the power

system management

. The LTC3886

FAULT

pins are configurable to indicate

a variety of faults including

OV, UV, OC,

OT,

timing faults and peak current faults.

In addition, the

FAULT

pins can be pulled

low by external sources, indicating a fault

in some other portion of the system. The

fault responses of the LTC3886 are configu-

rable and allow the following options:

• Ignore

• Shut Down Immediately—latchoff

• Shut Down Immediately—retry

indefinitely at the time interval

specified in

MFR_RETRY_DELAY

Table 1. Summary of Linear’s power system management controllers and PSM µModule regulators

µMODULE REGULATORS

LTM4675

LTM4676A

LTM4677

CONTROLLERS

LTC3880

LTC3882

LTC3883

LTC3884

LTC3886

LTC3887

OUT

range (V)

OUT

accuracy (%)

Input current sense

OUT

max (A)

DCR sensing

Digitally adjustable

loop compensation

Controller

0.5–5.5

4.5–17

0.5

calibrated

dual 9 or

single 18

0.5–5.5

4.5–17

0.5

calibrated

dual 13 or

single 26

0.5–5.5

4.5–17

0.5

calibrated

dual 18 or

single 36

0.5–4.0, ch0

0.5–5.4, ch1

4.5–24

0.5

inferred

30/phase

low

0.5–5.3

3.0–38

0.5

0.5–5.4

4.5–24

0.5

0.5–5.4

4.5–38

0.5

0.5–13.2

4.5–60

0.5

0.5–5.5

4.5–24

0.5

inferred

30/phase

low

40/phase

ultralow

30/phase

low

30/phase

very low

30/phase

low

maximum I

OUT

depends on external components

4 | February 2016 :

LT Journal of Analog Innovation

design features

Figure 1. The LTC3886 is versatile and flexible. It features wide input and output ranges

and and it is highly customizable via PMBus. Accurate telemetry is also available over

the digital bus. All features can be controlled via LTpowerPlay.

4.5V TO 60V

LTC3886

HOST

COMPUTER

PMBus/

SMBus/

ACCURACY AND PRECISION

UP TO SIX PHASES

CHANNEL1

0.5V TO 13.8V

≤30A

LOAD

SENSE1

PROGRAMMABLE

LOOP COMPENSATION

EEPROM

DATA LOGGING

SENSE0

OR CURRENT SHARE

≤60A

CHANNEL1

0.5V TO 13.8V

≤30A

LOAD

SENSE0–

Modern applications require supply

voltage regulation and supervision with

stringent tolerances. These requirements

are met with a high speed analog control

loop and an integrated

6-bit

ADC

and

2-bit

DAC

. The output voltage accuracy

of the LTC3886 is guaranteed at ±0.5%

over the full operating temperature. In

addition, the output voltage overvolt-

age and undervoltage comparators have

less than ±2% error over temperature.

The LTC3886’s regulation and supervi-

sion accuracy reduces total system costs

with fewer output capacitors, while

still meeting the tight input voltage

requirements of downstream

The unique high side 60

input current

sense amplifier measures the input current

with less than ±

.2% error over tempera-

ture. The output current is guaranteed

accurate to ±

.5% over temperature. The

internal die temperature measurement

of the LTC3886 is guaranteed accurate

to 0.25°

, and the external temperature

telemetry has less than ±

error.

FAULT LOGGING AND TELEMETRY

The LTC3886 supports fault logging,

which stores telemetry and fault status

data in a continuously updated

RAM

buffer. After a fault event occurs, the

buffer is copied from

RAM

EEPROM

and becomes a persistent fault log,

which can be read back at a later date

to determine what caused the fault.

EXTV

PIN FOR MAXIMUM

EFFICIENCY

The

EXTV

pin is provided to minimize

application power loss and supports

voltages of 5

It enables designs

with optimal circuit efficiency and

minimal die temperature, and enables

the LTC3886 to efficiently supply its own

bias power from the output voltage.

Figure 2. LTpowerPlay

February 2016 :

LT Journal of Analog Innovation

| 5

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