December 2000 - Linear Technology

Linear Technology Chronicle

• December 2000 1

A Showcase of Linear Technology’s Focus Products

Product of the Month

, LTC and LT are registered trademarks of Linear Technology

Corporation. No Latency ∆Σ, Hot Swap and Burst Mode are

trademarks of Linear Technology Corporation.

Linear Technology Chronicle

December 2000 Vol. 9 No. 12

Inside This Issue:

Four Tiny New Inductorless DC/DC Converters: High Frequency, Very Low Noise and Load

Disconnect in Shutdown—LTC1751, LTC1754, LTC3200, LTC1928-5 ................................. 2

Hot SwapTM Control of Power “Brick” Module with EM Filtering—LT1640 .............................. 3

Eliminate Two Step-Down DC/DC Converters with 550kHz Dual Controller—LTC1874........ 3

High Performance Op Amps in SOT-23—LT1797,

LT1812, LT1393

Linear Technology has made several

additions to its family of high performance

op amps in the tiny SOT-23 package.

The LT

1797 is a 10MHz, rail-to-rail

input and output op amp. This unity-gain

stable op amp brings precision and band-

width to the SOT-23 package. It operates on

single and split supplies with a total supply

voltage of 2.7V to 12V. It is fully specified

for operation at 3V/5V single supply as well

as ±5V dual supplies. This wide operating

supply range offers flexibility in a multitude

of applications. The rail-to-rail input and

output maximize dynamic range, an espe-

cially important feature in low voltage appli-

cations. DC precision has not been

neglected. The LT1797 offers a maximum

offset voltage of 1.5mV.

The LT1797 is available in both com-

mercial and fully specified industrial tem-

perature grades. Competing “guaranteed by

design” SOT-23 op amps are only tested at

room temperature and use statistical correla-

tion to predict temperature performance.

The LT1797 is tested and performance is

guaranteed over the entire –40°C to 85°C

industrial temperature range.

Previously only available in SO-8 but

now introduced in SOT-23, the LT1812 is

designed for high speed (100MHz GBW),

low noise (8nV/ ) applications where

low power consumption (3.6mA maximum

supply current) is at a premium. DC perfor-

mance has not been neglected with a 1.5mV

maximum offset voltage. The LT1812 is

offered in I grade, guaranteed and tested

over the entire –40°C to 85°C industrial

temperature range.

For higher speed applications, Linear

Technology now offers the LT1395 in

SOT-23. Perfect for video applications, the

LT1395 offers 400MHz bandwidth,

800V/µs slew rate and a maximum supply

current of 6.5mA. The 80mA output current

drive makes the part suitable for use as a

line or cable driver. The LT1395 runs on

supplies as low as ±2V to ±6V or 4V to

12V single supply.

Table 1 offers a summary of these addi-

tions to Linear Technology’s family of high

performance SOT-23 op amps.

Table 1. High Performance Op Amps in SOT-23

Part GBW SR V

SUPPLY

Output Temp Package

LT1797 10MHz 2.25V/µs 1.5mV 1.5mA 2.7V to 12.6V R-to-R C, I SOT-23

In/Out

LT1812 100MHz 750V/µs 1.5mV 3.6mA 4V to 12V C, I SOT-23,

SO-8

LT1395 400MHz 800V/µs 10mV 6.5mA 4V to 12V C SOT-23,

SO-8

√Hz

Differential 24-Bit ADC

Offers Simultaneous

50Hz and 60Hz

Rejection—LTC2413

The LTC

2413 is an accurate, simple,

and small 24-bit No Latency ∆Σ

ΤΜ

analog-

to-digital converter (ADC) that offers differ-

ential inputs and simultaneous 50Hz and

60Hz rejection. This device enables direct

digitization of inputs in applications such as

weigh scales, temperature measurements,

gas analyzers and strain gauge transducers

with no microprocessor calibration and no

external components. With simultaneous

50Hz and 60Hz rejection, the LTC2413 re-

jects line noise to better than 87dB anywhere

in the world regardless of the country’s line

frequency standards.

The LTC2413 includes all the outstand-

ing features of Linear Technology’s family

of No Latency ∆Σ analog-to-digital convert-

ers (see Table 1), eliminating configuration

and calibration registers, external compo-

nents and special filtering that other high

resolution ADCs require. Its high accuracy

differential nonlinearity (DNL) guarantees

true 24-bit performance with no missing

Continued on page 3

REF

–

SDO

SCK

–

GND

REF

350Ω

BRIDGE 13

2413 F42

1, 7, 8, 9,

10, 15, 16

LTC2413

R1 AND R2 CAN BE USED TO INCREASE TOLERABLE

AC COMPONENT ON REF SIGNALS

LT1019

Figure 1. Simple Bridge Connection

Linear Technology Chronicle

• December 2000

Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com.

Four Tiny New Inductorless DC/DC Converters: High Frequency, Very Low

Noise and Load Disconnect in Shutdown—LTC1751, LTC1754, LTC3200,

LTC1928-5

Four new DC/DC converters with

unique features are optimized for very small

space in portable products (see Table 1).

Three are micropower, drawing under

200µA of supply current. Two have soft-start

for controlled power up. One has very high

constant frequency for low interference in

RF sensitive products. One includes a linear

regulator for low noise and improved regula-

tion. All four require no inductors and only

three or four tiny ceramic chip capacitors.

All four work from single-cell Li-Ion batter-

ies with inputs as wide as 2V to 5.5V. All

switch at high frequencies from 550kHz to

2MHz, for small size and low ripple. In shut-

down mode, VIN is disconnected from the

output to eliminate battery drain and VOUT

is automatically grounded for fault-free

operation in all versions. All versions offer

short-circuit and thermal protection.

LTC1754 and LTC1751: Micropower,

SOT-23 and MSOP, 50mA and 100mA

The LTC1754 is a micropower charge

pump in a 6-lead SOT-23 package that pro-

duces up to 50mA of output current. It draws

just 13µA of quiescent current, 1µA in shut-

down mode, prolonging battery life. The

LTC1754-5 requires only a 1µF flying

capacitor, a small 10µF bypass capacitor at

VIN and another at VOUT to form a

complete boost converter circuit that fits into

a PC board space of just 0.05 square inches.

The LTC1754 meets the power source re-

quirements for cellular phones, bar code

readers, handheld computers and portable

instruments (Figure 1). It comes in 3.3V or

5V output versions.

The LTC1751 is a micropower charge

pump in the low height (1.1mm max) 8-lead

MSOP package that produces up to 100mA

of output current. This device plus three

small capacitors form a complete boost con-

verter circuit that fits into a board space of

0.06 square inches (39mm2). The LTC1751

includes an internal doubler charge pump

that boosts a 2V to 5.5V input to an adjust-

able 2.5V to 5.25V output. Its low operating

current (20µA) and shutdown current

(0.01µA typically) extend battery operating

time. The LTC1751 is also available in fixed

3.3V and 5V output versions (Figure 2). The

power good pin (PGOOD) on the fixed out-

put versions indicates when the output volt-

age has reached its final value or if the

output has an undervoltage fault condition.

The built-in soft-start feature is optional and

adjustable.

LTC3200: New Architecture for Constant

Frequency, SOT-23 and MSOP, 100mA

A new design allows the LTC3200 to

maintain constant frequency switching down

to zero load current. The result is reduced

output and input ripple. This voltage doubler

produces a regulated output voltage with up

to 100mA of current from a 2.7V to 4.5V

input. A variable output version in MSOP

and a fixed 5V output version in SOT-23 are

available. The tiny package plus just three

tiny capacitors make the LTC3200 ideally

suited for small battery-powered products

where low noise is important. Built-in soft-

start circuitry prevents excessive inrush cur-

rent during start-up. Its shutdown feature

reduces quiescent current to under 1µA. The

LTC3200 is perfect for LED backlight sup-

plies for color LCD displays (Figure 3) and

for local 3V to 5V conversion such as

required for PCMCIA systems.

LTC1928-5: Micropower, SOT-23, 30mA,

Internal Linear Regulator

The LTC1928-5 takes the standard dou-

bler architecture and adds an internal low

dropout voltage linear regulator to reduce

ripple and improve regulation. Competing

solutions require two ICs. The LTC1928-5

has an output voltage ripple of 90µVRMS

(100kHz bandwidth) while delivering up to

30mA of output current. It draws just 190µA

of operating current (4µA in shutdown)

which makes it ideal as a VCO power supply

in cellular phones where it is very important

to minimize output noise while prolonging

battery life. The LTC1928-5 converts a 2.7V

to 4.4V input supply to produce a fixed 5V

output and requires only four external

capacitors resulting in a circuit footprint of

just 34mm2 (<0.045in2). The 550kHz

switching frequency operation permits the

use of small ceramic capacitors to save

board space. Due to the internal current lim-

iting, the output current VOUT can be shorted

to ground indefinitely. The LTC1928-5 is

offered in a 6-lead SOT-23 package and is

specified over a –40°C to 85°C operating

temperature range. Also shown in Table 1 is

the similar LTC1682. This MSOP package

device provides up to 80mA of output cur-

rent and comes in adjustable, 3.3V and 5V

output versions.

546

LTC1754-5

1µF

1754 TA06

10µF 10µF

OUT

5V ±4%

50mA

USB

PORT

SHDN

GND

OUT

PGOOD

–

LTC1751-5

OUT

5V ±4%

OUT

≤ 100mA, V

≥ 3V

OUT

≤ 50mA, V

≥ 2.7V

2.7V

TO 5.5V C2

10µF

FLY

1µF

PGOOD

100k

ON OFF

1751 TA01

10µF

4.7nF

Figure 2. Regulated 5V Output from 2.7V to 5.5V

Figure 1. USB Port to Regulated 5V

Power Supply

1µF

LTC3200

C+C–

VOUT

ON OFF PGND

VIN

SHDN

SGND 5

682Ω

32005 TA04

1µF

82Ω

UP TO 6 LEDS

82Ω82Ω82Ω82Ω

3V TO 4.4V

Li-Ion

BATTERY 1µF

VSHDN

(APPLY PWM WAVEFORM FOR

ADJUSTABLE BRIGHTNESS CONTROL) t

Figure 3. White or Blue LED Driver with LED Current Control

Linear Technology Chronicle

• December 2000 3

Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com.

Application of the Month

Hot Swap Control of a Power “Brick” Module with EMI Filtering—LT1640

Figure 1. Hot Swap Application Using a Filter Module

The LT1640 is a negative voltage Hot

Swap controller that allows a board to be

safely inserted and removed from a live

backplane. Inrush current is limited to a

programmable value by controlling the gate

voltage of an external N-channel pass tran-

sistor. The pass transistor is turned off if the

input voltage is less than the undervoltage

threshold (programmable) or greater than

the overvoltage threshold. A programmable

electronic circuit breaker protects the sys-

tem against shorts. The LT1640 works

directly with voltages ranging from –10V to

–80V and has proven popular in –48V

telecom systems.

It provides a power good output that can

directly enable a power module when the

input voltage to the module is within toler-

ance, without floating supplies or level shift-

ing. The LT1640L version is designed for

modules with an active-low enable and the

LT1640H for modules with an active-high

enable.

Many applications place an EMI filter

module in the power path to prevent switch-

ing noise of the module from being injected

back onto the power supply. A typical appli-

cation using the Lucent FLTR100V10 filter

module is shown in Figure 1. When using a

filter, an optoisolator is required to prevent

1kV common mode transients—standard

fare for telecom equipment—from destroy-

ing the PWRGD and ON/OFF pins.

For positive 48V inputs, the LTC1641

provides a similar capability. Each of these

controllers is available in an 8-pin SO pack-

age. The power brick module may be

replaced with a design based upon the

LT1339, LT1247 or LT1425 switching

regulator controllers. (See InfoCards 23

and 25.)

LT1640L

PWRGD

SENSE

150nF

25V

3.3nF

100V

0.1µF

100V

0.1µF

100V

0.1µF

100V

100µF

100V

100µF

16V

IRF530

10Ω

18k

562k

9.09k

10k

0.02Ω

GND

–48V

GATE

DRAIN

LUCENT

JW050A1-E

OUT+

SENSE

TRIM

SENSE

–

OUT–

IN+

95V

1640 F14

ON/OFF

CASE

IN–

OUT+

OUT–

IN+

CASE

IN–

LUCENT

FLTR100V10

(SHORT PIN)

1N4148

* DIODES INC. SMAT70A

OPTOISOLATOR

codes and its integral nonlinearity (INL) is

only 2ppm. The No Latency architecture

ensures single cycle settling time,

Table 1. No Latency ∆Σ Analog-to-Digital Converters

1-Channel 2-Channel 4-Channel 8-Channel

800nV Noise LTC2410*

24 Bits LTC2413*

1.5µV Noise LTC2400 LTC2404 LTC2408

24 Bits LTC2411*

3µV Noise LTC2401 LTC2402

24 Bits

6µV Noise LTC2420 LTC2424 LTC2428

20 Bits

*Differential Inputs

simplifying multiplexed applications and

eliminating software overhead. A full-scale

error of just 2.5ppm and 800nVRMS noise

LTC2413 from page 1

allow direct connection to sensors and

bridges without the use of a PGA.

The LTC2413’s differential inputs

allow direct connection to bridges without

external circuitry (Figure 1). The LTC2413

also offers differential reference inputs,

which can range from 0.1V up to VCC for

ratiometric and remote sensing applications.

The input voltage range is –0.5VREF to

0.5VREF. The LTC2413 operates on supply

voltages from 2.7V to 5.5V, consuming just

200µA during conversion and 20µA during

shutdown.

The LTC2413 is available in the space

saving 16-pin SSOP package in the commer-

cial and industrial temperature ranges.

Linear Technology Chronicle

• December 2000

Linear Technology Corporation • 1630 McCarthy Blvd. • Milpitas, CA 95035-7417 • (408) 432-1900 • FAX: (408) 434-0507 • www.linear-tech.com • For Literature Only: 1-800-4-LINEAR

Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com.

LTC1751, LTC1754, LTC3200, LTC1928-5 from page 2

Table 1. New Inductorless DC/DC Voltage Converters Are Optimized by Application

Parameters* LTC1751 LTC1754 LTC3200 LTC1928-5 LTC1682

Architecture Gated Oscillator Constant Open Loop Charge Pump

with Burst Mode Frequency with LDO Post Regulator

Advantages Highest Efficiency, Moderate Low Noise, Lowest Noise, Low I

Noise, Lowest I

Lowest RFI Best Regulation

Additional Features Power Good, Tiniest Auto Soft-Start, Stable with 2µF Capacitor

UVLO, Soft-Start Tiniest On the Output

Input Voltage 2V to 5.5V 2V to 4.4V 2.7V to 4.5V 2.7V to 4.4V 1.8V to 4.4V

Output Voltages 3.3V, 5V, 3.3V, 5V 5V, 5V 3.3V, 5V,

2.5V ~ 5.25V 3V ~ 5.5V 2.5V ~ 5.5V

Regulation 4% 4% 4% 2% 2%

Output Current 100mA 50mA 100mA 30mA 80mA

Switching Frequency 800kHz 600kHz 2MHz 550kHz 550kHz

Typical Efficiency** 83% 83% 79% 79% 78%

OUT

Ripple (2.5MHz BW) 68mV

P-P

65mV

P-P

— 800µV

P-P

500µV

P-P

Narrow Band Ripple (100kHz) — — 3 to 33mV

P-P

90µV

RMS

60µV

RMS

Typical Quiescent Current 20µA13µA 4mA 190µA 150µA

Typical Shutdown <2µA<1µA<1µA4µA1µA

Packages MSOP-8 SOT-23 SOT-23 SOT-23 MSOP-8

MSOP-8 SO-8

* Maximum/minimum values unless stated as typical.

** 3V input to 5V output, for comparison. See data sheets.

Eliminate Two Step-

Down DC/DC Converters

with 550kHz Dual

Controller—LTC1874

The LTC1874 is a dual output current

mode step-down DC/DC converter that

includes two 550kHz controllers in a small,

thin 16-lead SSOP. This IC replaces two

DC/DC converters and allows the use of

small inductors and capacitors. The input

voltage range for each controller is 2.5V to

10V with output adjustable to as low as

0.8V. Each controller consumes only 270µA

but can deliver up to 5A of load current. The

IC’s compact dual output voltage design is

ideal in powering ASICs, microcontrollers,

memory modules and DSPs in applications

ranging from telecom to portable devices.

The LTC1874 drives external P-channel

MOSFETs and uses sense resistors to accu-

rately deliver power to the load at up to 94%

efficiency. Furthermore, the use of P-chan-

nel MOSFETS maximizes the life of a bat-

tery source by allowing very low dropout

operation. Each controller has a separate

shutdown pin allowing full control of each

output voltage.

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