LTJournal_V20N4_Jan11.pdf

January 2011

Volume 20 Number 4

IN THIS ISSUE

TimerBlox: Function-Speciic ICs

Quickly and Reliably Solve

Timing Problems

Andy Crofts

solar battery charger tracks

panel maximum power 10

I 2 C system monitor

combines temperature,

voltage and current

measurements 22

isolated data transmission

and power conversion

combo in surface mount

package 30

Your design is nearly complete, but a nagging timing requirement

has suddenly cropped up. It might call for a variable frequency

oscillator, a low frequency timer, a pulse-width modulator, a

controlled one-shot pulse generator, or an accurate delay.

Regardless of the requirement, you need a quick, reliable, stable

solution—there is no time to develop code for a microcontroller. You

could build something out of discrete components and a comparator

or two, or maybe the good old 555 timer could do the job, but will

the accuracy be there? Will it take up too much room on the board?

What about time to test and specify the bench-built timer?

isolated power supplies

made easy 38

nanopower buck converter

for energy harvesting apps

POWER

SUPPLY

CONNECTOR

DROPS

WIRING DROPS CONNECTOR

DROPS

LOAD

There is a better way. L i near Technology’s TimerBlox ® fam-

ily of silicon timing devices solves speciic timing problems with

minimal effort. TimerBlox devices easily drop into designs with a

fraction of the design effort or space requirements that a micro-

controller or discrete-component solution would demand. It only

takes a few resistors to nail down the frequency or time dura-

tion you require. That’s it , no coding or testing required. Complete

solutions are tiny , composed of a 2mm × 3mm DFN , or a popular

6-lead SOT-23 , plus a couple of resistors and decoupling cap.

CONNECTOR

DROPS

WIRING DROPS

CONNECTOR

DROPS

Figure 1. The simplest model for load regulation over

resistive interconnections.

A TOOLBOX OF TIMERBLOX DEVICES

All TimerBlox devices use L i near’s silicon oscillator technology ,

featuring low component count , vibration-immunity , fast start-

up , and ease-of-use. Each TimerBlox device is purpose-built to

solve a speciic timing problem (see Table 1 ) , so the performance

(continued on page 2)

TimerBlox devices solve timing problems

www.linear.com

…continued from the cover

In this issue...

It only takes a few resistors to nail down the frequency

or time duration you require. That’s it, no coding or

testing required. Complete solutions are tiny, composed

of a 2mm × 3mm DFN, or a popular 6-lead SOT-23,

plus a couple of resistors and decoupling cap.

COVER STORY

TimerBlox: Function-Speciic ICs Quickly

and Reliably Solve Timing Problems

Andy Crofts

DESIGN FEATURES

( LTC 699x, continued from page 1)

Battery Charger’s Unique Input

Regulation Loop Simpliies Solar Panel

Maximum Power Point Tracking

Jay Celani

of each device is speciied for its intended application , eliminating the

guesswork involved with coniguring and applying do-it-all timers.

Because each TimerBlox device is designed to perform a speciic timing func-

tion , the most signiicant design decision is choosing the proper part number.

To further simplify design , ive of the six package pins in all TimerBlox devices

share the same name and function—with the remaining pin unique to the

device function. Figure 1 details the function of each pin (SOT-23 shown).

Two High Power Monolithic Switching

Regulators Include Integrated 6A, 42V or

3.3A, 42V Power Switches, Built-in Fault

Protection and Operation up to 2.5MHz

Matthew Topp and Joshua Moore

Each Timerblox device offers eight different timing ranges and two modes

of operation (which vary for each device). The operational state is rep-

resented by a 4-bit DIVCODE value , which is set by the voltage on the

DIV pin. For the ultimate in simplicity , a resistor divider can be used to

set the DIVCODE. For example , Figure 2 shows how changing the volt-

age at the DIV pin sets the functionality of the LTC6992 by selecting a

DIVCODE from 0– 1 5. The MSB of DIVCODE is a “mode” bit , in this case select-

ing the output polarity. The remaining bits choose the frequency range.

I 2 C System Monitor Combines Temperature,

Voltage and Current Measurements

for Single-IC System Monitoring

David Schneider

Isolated Data Transmission and Power Conversion

Integrated Into a Surface Mount Package

Keith Bennett

Isolated Power Supplies Made Easy

John D. Morris

Once the proper DIVCODE has been determined , the frequency or tim-

ing duration is ine-tuned by a simple calculation for R SET . The set

resistor establishes the frequency of an internal silicon oscillator mas-

ter clock. The resulting circuit has guaranteed accuracy over the full

2.25V–5.5V supply range and –40 ° C to 1 25 ° C temperature range.

DESIGN IDEAS

Nanopower Buck Converter Runs on

720nA, Easily Fits into Energy Harvesting

and Other Low Power Applications

Michael Whitaker

(continued on page 4)

product briefs

back page circuits

Figure 1. All TimerBlox devices share common pin functions

DEVICE-SPECIFIC FUNCTION PIN

LTC6990: Output Enable

LTC6991: Reset

LTC6992: Modulation Control

LTC6993: Trigger

LTC6994: Logic Input

OUTPUT

Sources and Sinks 20mA

SUPPLY VOLTAGE

2.25V TO 5.5V

Scan This

OUT

CONTROL RESISTOR

Allows for VCO Operation

LTC699x

V +

SCAN THIS CODE WITH

YOUR SMART PHONE

Most smart phones support QR

Code scanning using their built-in

cameras. Some phones may require that you

download a QR Code scanner/reader application.

This code links to www.linear.com/ltjournal .

GND

V +

C 1

0.1µF

R VCO (OPTIONAL)

RESISTOR DIVIDER SETS V DIV

Voltage at DIV (Divider) Pin Selects

One of 16 States, which Sets the

Output Frequency Range

and Mode Bit

SET

DIV

CONTROL VOLTAGE

Modulates Output Frequency

R SET

SET RESISTOR

Only a Single Resistor is Required

to Set the Master Frequency

2 | January 2011 : LT Journal of Analog Innovation

Linear in the news

Linear in the News

APEC SHOW

Linear will have a booth at APEC , the

Applied Power Electronics Conference

and Exposition , held in Fort Worth , Texas ,

March 6- 1 0. At the booth ( 1 5 1 and 1 52) ,

L i near will showcase a broad range of

power management solutions , including:

vehicles , as well as H-grade power man-

agement IC s for automotive applica-

tions and power µModule regulators.

Information at www.car-ele.jp / carele / en .

EVENTS IN CHINA

IIC China Conference & Exhibition, Shenzhen

Convention & Exhibition Center, Shenzhen, China,

February 24–26: IIC China is attended by

design engineers and technical man-

agers in China. It is China’s largest

showcase of IC application technologies

and high-end components. At L i near’s

booth (2C 1 5) , visitors will gain an

overview of the company’s products

across a range of diverse applications.

Info at www.english.iic-china.com .

Advanced Automotive Batteries Conference,

Pasadena Convention Center, Pasadena, California,

January 24–28: L i near will showcase the

company’s innovative battery manage-

ment IC family. including the LTC6802 , a

highly integrated multicell battery moni-

toring IC capable of precisely measuring

the voltages of up to 1 2 series-connected

battery cells. Using a novel stacking

technique , multiple LTC6802s can be

placed in series without opto-couplers

or isolators. Stacked LTC6802s enable

precision measurement of all battery

cell voltages , independent of battery

string size , within 1 3ms. L i near will also

show the companion LTC680 1 indepen-

dent multicell battery stack monitor

and other devices in the family. Info at

www.advancedautobat.com / automotive-

battery-conference-20 11 /index.html .

•Energy harvesting solutions

•Power µModule ® regulators

•Digital power products

•LED drivers

•Linear regulators

•Switching regulators

Electronica & Productronica China 2011, Shanghai

New International Expo Center, Shanghai, China,

March 15–17: This is the 1 0th anniver-

sary of Electronica & Productronica.

The show focuses on the latest technol-

ogy breakthroughs in growth-oriented

markets , including telecommunications ,

industrial , automotive and IT prod-

ucts , and consumer electronics. L i near

will be in Hall E2 , booth 2466. More

info at e-p-china.com / en / home .

The booth will be staffed by L i near’s

power experts and technical ield

staff. Info at www.apec-conf.org .

AUTOMOTIVE SHOWS

Linear Technology is rapidly growing its

commitment to the automotive electron-

ics market. This parallels the increase in

the electronics content in cars , as well as

new innovations in hybrid and electric

vehicles. L i near’s products for automo-

tive now cover most electronics systems

including navigation and entertainment ,

safety systems , security , electronic steer-

ing and braking , LED lighting , engine

control and battery management sys-

tems for hybrid / electric vehicles.

At both IIC China and Electronica

& Productronica , L i near will

showcase the following:

SAE 2011 Hybrid Vehicle Technology Symposium,

Hilton Anaheim, Anaheim, California, February 9– 11:

At this automotive-focused conference ,

L i near will showcase its growing fam-

ily of battery stack monitors for hybrid /

electric vehicles. This conference will

focus on technology advances and

platform strategies for hybrid / electric

vehicles , plug-in hybrid electric vehicles

and all-electric vehicles. Info at www.sae.

org / events / training / symposia / hybrid .

•Automotive electronic solutions

•Battery management systems

for hybrid / electric vehicles

•Wireless communications solutions

•Industrial & medical solutions

•Instrumentation

•Energy harvesting/ Nanopower solutions

•High power LED drivers

•High voltage step-down

(buck) regulators

•TimerBlox product family

•Power µModule regulators n

Linear plans to participate with

booths at the following automo-

tive events in the coming months:

International Automotive Electronics Technology

Expo, Tokyo Bigsight Convention Center, Japan,

January 19–21: At this show , L i near will

showcase its LTC6802 family of bat-

tery management IC s for hybrid / electric

January 2011 : LT Journal of Analog Innovation | 3

The LTC6990 can easily be used as a voltage-controlled

frequency modulator. Although this technique can be

used with other silicon oscillators, they typically are

limited in accuracy and suffer from poor supply rejection.

The LTC6990 does not have these limitations.

( LTC 699x, continued from page 2)

Figure 2. LTC6992

Frequency Range and

“POL” Bit vs DIVCODE

1000

DIVCODE MSB (“POL” BIT) = 0

DIVCODE MSB (“POL” BIT) = 1

For an even easier design process ,

download “ The TimerBlox Designer ”

from www.linear.com / timerblox —

a free Excel-based tool that gener-

ates component values , schematics ,

and timing diagrams automatically.

100

0.1

0.01

VOLTAGE-CONTROLLED

OSCILLATOR CAN BE USED FOR

FIXED FREQUENCY OR FREQUENCY

MODULATION

The LTC6990 is a resistor-programmable

oscillator featuring 1 .5% accuracy and

an output enable function to force the

output low or into a high-impedance

state. The output frequency is deter-

mined by the N DIV frequency divider

and R SET (which replaces V SET / I SET ):

0.001

¼V +

½V +

¾V +

V +

INCREASING V DIV

output frequency. Although this technique

can be used with other silicon oscillators ,

they typically are limited in accuracy and

suffer from poor supply rejection. The

LTC6990 does not have these limitations

because of three important enhancements:

•All TimerBlox devices allow for a

wide 1 6: 1 timing range within each

N DIV setting , but only the LTC6990 uses

a small 2× step through divider set-

tings. That allows for maximum over-

lap between ranges to accommodate

any 8: 1 range of VCO frequencies (or

1 6: 1 with a reduced-accuracy extended

range). And since each TimerBlox

device has eight different timing

ranges , the LTC6990 still maintains a

large 4096: 1 total frequency range.

MHz k

•

SET

•V SET (the SET pin voltage) is regulated

to 1 V and is accurate to ±30 m V over

all conditions. This allows R VCO to

establish an accurate VCO gain.

OUT

where N DIV = 1, 2, 4, …, 128

While it can be used as a ixed-frequency

oscillator , the LTC6990 can easily be

applied as a frequency modulator. A

second SET-pin resistor , R VCO , allows a

control voltage to vary I SET and change the

DIV

•V SET is GND-referenced , allowing

for a GND-referenced control volt-

age that is easy to work with.

Figure 3 shows the LTC6990 conigured as

a VCO that translates a 0V to 3.3V control

Figure 3. LTC6990 voltage-controlled oscillator

Figure 4. Performance of the voltage-controlled

oscillator shown in Figure 3

40kHz TO 400k H z

OUTPUT

ENABLE

OUT

f OUT = 400kHz − V CTRL • 109 kHz

2V/DIV

LTC6990

V +

GND

V +

0.1µF

V CTRL

2V/DIV

R VCO

232k

976k

DIVCODE = 1

(N DIV = 2, Hi-Z = 0)

V CTRL

0V to 3.3V

SET

DIV

R SET

8 6.6k

1 02k

OUT

2V/DIV

20µs/DIV

4 | January 2011 : LT Journal of Analog Innovation

cover story

DEVICE

FUNCTION

OPTIONS

RANGE

OUTPUT

ENABLE

V CTRL

Voltage-Controlled

Silicon Oscillator

Configurable frequency gain and voltage range

488Hz to 2MHz

OUTPUT

RESET

Low Frequency Oscillator

Period range from 1ms to 9.5 hours

29µHz to 977Hz

LTC6992-1

0%–100% Duty Cycle

PWM

CONTROL

LTC6992-2

5%–95% Duty Cycle

Voltage-Controlled PWM

3.8Hz to 1MHz

LTC6992-3

0%–95% Duty Cycle

LTC6992-4

5%–100% Duty Cycle

LTC6993-1

Rising-Edge Triggered

TRIGGER

LTC6993-2

Rising-Edge Re-Triggerable

One-Shot

1µs to 34 sec

LTC6993-3

Falling-Edge Triggered

LTC6993-4

Falling-Edge Re-Triggerable

INPUT

LTC6994-1

1-Edge Delay

Delay

1µs to 34 sec

LTC6994-2

2-Edge Delay

Table 1. TimerBlox family members

voltage into a 40 k H z to 400 k H z fre-

quency. Due to the LTC6990’s high

modulation bandwidth , the output

responds quickly to control voltage

changes , as can be seen in Figure 4.

Since the applications for frequency

modulation are rare at such low fre-

quencies , the emphasis for this part is

on covering as wide a range as possible.

Therefore , the LTC699 1 uses large 8×

steps between N DIV settings. The trade-off

is a smaller 2× overlap between ranges.

The output interval relationship is:

output enable , it includes a similar reset

function. The RST pin can truncate the

output pulse or prevent the output from

oscillating at all , but it has no effect

on the timing of the next rising edge.

This function allows the LTC699 1 to

initiate an event with a variable dura-

tion , perhaps controlled by another

circuit. Otherwise , if RST is inactive , the

LTC699 1 produces a square wave.

LOW FREQUENCY SOLUTIONS

The LTC699 1 picks up in frequency where

the LTC6990 leaves off , with an enor-

mous 29 µ H z to 977H z range (a period

range of 1 ms to 9.5 hours). It incorpo-

rates a ixed 1 0-stage frequency divider

and a programmable 2 1 -stage divider.

OUT

•

1 024

where N DIV = 1, 8, 64, …, 2 21

The LTC699 1 is designed to handle long

duration timing events. In place of an

Figure 5 shows how a simple camera

intervalometer can be constructed from

the LTC699 1 and a handful of discrete

January 2011 : LT Journal of Analog Innovation | 5

•

DIV SET

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