January 2001 - Linear Technology

Linear Technology Chronicle

• January 2001 1

A Showcase of Linear Technology’s Focus Products

Product of the Month

, LTC and LT are registered trademarks of Linear Technology

Corporation. Burst Mode and Hot Swap are trademarks of Linear

Technology Corporation.

Linear Technology Chronicle

January 2001 Vol. 10 No. 1

Inside This Issue:

High Performance Sine Wave to Square Wave Converter—LT1719 ..................................... 3

Industry’s Fastest Rail-to-Rail Input/Output Comparator Has 4.5ns Prop Delay—LT1712 .... 3

Dual N-Channel High Side Switch Controller in SOT-23 Draws Just 10µA—LTC1982.......... 4

Comparator with Latch: 7ns, Rail-to-Rail Input and Output—LT1713..................................... 4

Tiny Step-Down Switching Regulators Operate at

Very High Frequency—LTC3404/LT1767/LTC1773

Part 1: New Switching Regulators in MSOP

New miniature high frequency switch-

ing regulators greatly expand the options

available to designers of portable and com-

munications products. Four of these new

products are supplied in the tiny MSOP

package that is very thin (1.1mm maximum)

and half the size of an SO-8. Each of these

four devices operates at high frequency for

very low ripple in sensitive bands and to

allow the use of tiny, low cost, surface

mount inductors and capacitors. Each

switches at a constant frequency for ease of

filtering. These are all current mode

devices

for fast transient response and excellent loop

stability. They each operate at high duty

cycles (Table 1) resulting in very low drop-

out operation, which extends the battery run

time in portable systems. Three of the de-

vices provide logic-selectable Burst Mode

operation for ultralow power consumption

when the converter is operating with very

low load. These three devices have synchro-

nous rectification that increases efficiency

and eliminates the need for a Schottky

diode, saving components and board space.

LTC

3404: 1.4MHz Synchronous Buck

Converter Delivers 95% Efficiency

The LTC3404 is a 1.4MHz current

mode monolithic synchronous step-down

DC/DC capable of delivering up to 600mA

of output current (Figure 1). The LTC3404

offers the industry’s lowest operating quies-

cent current for monolithic devices, with

switching frequencies of 1MHz and higher.

Table 1: New High Frequency Step-Down Switching Regulators in MSOP

LTC3404 LTC1877* LT1767 LTC1773

OUT

Maximum 0.8A 0.8A 1.5A 7A**

Input Range 2.65V to 6V 2.65V to 10V 2.7V to 25V 2.65V to 8.5V

Switching Frequency

†

1MHz to 1.7MHz 400kHz to 700kHz 1MHz to 2MHz 550kHz to 750kHz

Synchronous Yes Yes No Yes

Peak Efficiency 95% 95% 90% 95%

REF

(Min V

OUT

) 0.8V 0.8V 1.2V 0.8V

Supply Current I

10µA10µA 1mA 80µA

Maximum Duty Cycle 100% 100% 90% 100%

Shutdown Current 1µA1µA6µA10µA

*Introduced September 2000 **Up to 3A with a small external complementary MOSFET device

†

Constant frequency devices. Burst Mode operation is logic selectable for the LTC3404, LTC1877 and

LTC1773.

22µF**

CER

LTC3404

GND

4.7µH*

10µF***

CER

220pF

OUT

†

3.3V

***

†

TOKO D52LC A914BYW-4R7M

TAIYO-YUDEN CERAMIC JMK325BJ226MM

TAIYO-YUDEN CERAMIC LMK325BJ106MN

OUT

CONNECTED TO V

FOR 2.65V < V

< 3.3V

887k

20pF

280k

3404 TA01

SYNC

RUN

2.65V

TO 6V

Figure 1. High Efficiency 800mA Step-

Down Converter Uses Tiny Components

Dual/Quad Zero Drift

Op Amps in Miniature

Packages Provide

Unprecedented

Accuracy—LTC2051/

LTC2052

Completing the family of zero drift

amplifiers that began with the single ampli-

fier LTC2050, Linear Technology now

offers the dual LTC2051 and quad

LTC2052. These DC accurate op amps fea-

ture a maximum input offset voltage of 3µV

and an almost negligible offset drift of

30nV/°C. The parts also offer 75pA of input

bias current, CMRR and PSRR in excess of

130dB and 140dB large-signal gain. With

this unparalleled DC precision, the

LTC2050, LTC2051 and LTC2052 can be

used to improve total system precision,

reduce material manufacturing costs by

Continued on page 2

Linear Technology Chronicle

• January 2001

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.

Its quiescent current of only 10µA (less than

1µA in shutdown) offers the highest effi-

ciency at low to moderate load currents. Its

input voltage range of 2.65V to 6V allows

operation with a single Li-Ion cell or mul-

tiple NiCd/NiMH batteries. Low output volt-

ages are supported with a 0.8V feedback

reference voltage. The LTC3404 is well

suited for a variety of wireless and commu-

nications applications, such as cell phones,

wireless modems, DSL modems and PDAs.

The LTC1877 is a similar device that

switches at 550kHz.

1767: 1.5A, 1.25MHz Step-Down

Regulator in an MSOP

The LT1767 is the industry’s only 1.5A

single chip, step-down switching regulator in

an MSOP that switches at over 1MHz (Fig-

ure 2). The input voltage range extends from

2.7V to 25V; thus, the LT1767 is suitable for

simplifying or even negating the need for

post assembly trim.

In addition to DC accuracy, this family

of op amps features a wide gain bandwidth

of 3MHz, a high slew rate of 2V/µs and low

DC to 10Hz noise of 1.5µV

P-P

. Rail-to-rail

output voltage swing and a wide input com-

mon mode range that includes ground make

these op amps ideal for use with a range of

sensors including thermocouples, airflow

meters, pressure sensors and any variety of

wheatstone bridge sensors (see Figure 1).

The LTC2050, LTC2051 and LTC2052

operate on supply voltages from 2.7V to

6Vand draw just 750µA per amplifier. For

regulating a wide range of power sources

from 4-cell batteries, 5V logic rails, unregu-

lated wall transformers and lead-acid batter-

ies. It is also useful for buck-boost SEPIC

converters.

A low dropout internal regulator main-

tains consistent performance over a wide

range of inputs. An operating supply current

of 1mA improves efficiency, especially at

lower output currents. Shutdown reduces

quiescent current to 6µA. High switch effi-

ciency is attained by using the BOOST pin

to provide a voltage to the switch driver that

is higher than the input voltage, allowing the

switch to be saturated. Full cycle-by-cycle

short-circuit protection and thermal shut-

down are provided.

LTC1773: Synchronous Step-Down Regu-

lator Controller

The LTC1773 is a synchronous regula-

tor controller that drives external comple-

mentary power MOSFETs using a fixed

frequency architecture. The operating supply

voltage is from 2.65V to 8.5V, making it

suitable for 1- or 2-cell Li-Ion battery pow-

ered products (Figure 3). The device uses

single package complementary MOSFET

switches, for outputs up to 1A in a TSSOP

package and to 3A in an SO-8. Up to 7A

may be regulated using two separate FETs.

The peak current limit is user programmable

with a high side sense resistor. A control pin

guarantees regulation of secondary windings

regardless of load on the main output by

forcing continuous operation. Burst Mode

operation, which provides high efficiency at

low load current, is inhibited during syn-

chronization or when the control pin is

pulled low, to reduce noise and RF interfer-

ence. Built-in soft-start limits inrush current.

The LTC1773 is useful for higher current

needs in cell phones, wireless

modems, RF power amp supplies and other

portable equipment.

LTC3404, LT1767, LTC1773 from page 1

BOOST

LT1767

OUTPUT

3.3V

1.4A

17.4k

10k

INPUT

1767 TA01

0.1µF

2.2nF D1

MBRS130T3

2.2µF

CERAMIC

1µF

CERAMIC

1N914

5µH

FBSHDN

OPEN

HIGH

= ON GND V

SYNC

30k

220pF

0.1µF

OUT

180µF

68µF

3µH

2.65V TO 8.5V

OUT

2.5V

SENSE

0.025Ω

1773 F01

LTC1773

RUN/SS

SYNC/FCB

GND

SENSE

–

SW Si9801DY

80.6k

169k

47pF

Figure 2. Step-Down 1MHz Switcher Converts

5V to 3.3V at 1.4A

LTC2051/LTC2052 from page 1

Figure 3. Step-Down Converter Provides 3A

Using Complementary FET in SO-8

applications requiring higher supply volt-

ages, all three parts are offered in HV ver-

sions that can operate on single or split

supplies from 2.7V to 11V. This expanded

supply range allows operation in the wide

range of applications requiring ±5V

supplies.

The LTC2050 is available in 5-pin

SOT-23 and with shutdown in the 6-pin

SOT-23 and SO-8 packages. The

LTC2050HV is available in the SO-8 pack-

age. The LTC2051 and LTC2051HV dual

op amps are available in both the tiny 8-pin

MSOP and the SO-8 packages. The

LTC2052 quad amplifier is available in the

16-pin SSOP (occupying the same footprint

as a standard SO-8) and 14-pin SO pack-

ages. All parts in this family of op amps are

available in both commercial and industrial

temperature grades.

–

10k

0.1%

100Ω

0.1%

20512 TA01

–5V

–

1/2

LTC2051HV 1/2

LTC2051HV

–V

= 101

10k

0.1%

100Ω

0.1%

Figure 1. High Performance Low Cost

Instrumentation Amplifier

Linear Technology Chronicle

• January 2001 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

High Performance Sine Wave to Square Wave Converter—LT1719

Propagation delay of comparators is

typically specified for a 100mV step with

some fraction of that for overdrive. But in

many signal processing applications, such

as in communications, the goal is to convert

a sine wave, such as a carrier, to a square

wave for use as a timing clock. The desired

behavior is for the output timing to be

dependent on the input timing only. No

phase shift should occur as a function of the

input amplitude, which would result in AM

to FM conversion.

The circuit of Figure 1 is a simple

LT1719-based sine wave to square wave

converter. The ±5V supplies on the input

allow very large swing inputs, while the 3V

logic supply keeps the output swing small to

minimize crosstalk. Figure 2 shows the time

delay versus input amplitude with a 10MHz

sine wave. The LT1719 delay changes just

0.65ns over the 26dB amplitude range, 2.33°

at 10MHz. The delay is particularly flat

yielding excellent AM rejection from 0dBm

to 15dBm. If a 2:1 transformer is used to

drive the input differentially, this exception-

ally flat zone spans –5dBm to 10dBm, a

common range for RF signal levels.

Similar delay performance is achieved

with input frequencies as high as 50MHz.

There is, however, some additional

encroachment into the central flat zone

by both the small amplitude and large

amplitude variations.

With small input signals, the hysteresis

and dispersion make the LT1719 act like a

comparator with a 12mV hysteresis span. In

other words, a 12mVP-P sine wave at

10MHz will barely toggle the LT1719, with

90° of phase lag or 25ns additional delay.

Above 5VP-P at 10MHz, the LT1719

delay starts to decrease due to internal

capacitive feedforward in the input stage.

Unlike some comparators, the LT1719 will

not falsely anticipate a change in input

polarity, but the feedforward is enough to

make a transition propagate through the

LT1719 faster once the input polarity

changes.

–

LT1719

50Ω

1719 F08a

SINE WAVE

INPUT SQUARE WAVE

OUTPUT

–5V

INPUT AMPLITUDE (dBm)

–5

TIME DELAY (ns)

051015

1719 F08b

20 25

632mV

P-P

6.32V

P-P

25°C

= 5V

= –5V

= 3V

10MHz

Figure 1. LT1719-Based Sine Wave to

Square Wave Converter

Industry’s Fastest Rail-

to-Rail Input/Output

Comparator Has 4.5ns

Prop Delay —LT1712

The LT1712 is the first dual comparator

in the industry that features 4.5ns propaga-

tion delay (see Figure 1), a rail-to-rail input

voltage range, complementary rail-to-rail

CMOS/TTL compatible outputs with inter-

nal data latches and an operating supply

range of 2.4V to 12V.

The LT1712 is more than just a fast

response comparator. Its 2.4V operation

combined with its rail-to-rail inputs and

CMOS compatible outputs makes it ideal

Figure 2. Time Delay vs Sine Wave Input

Amplitude

systems. The LT1712’s 12V operational

capability, high speed and small SSOP pack-

age make it equally well suited for use in

automatic test equipment. The dual internal

latches are ideal for data sampling applica-

tions. With rail-to-rail complementary out-

puts that can sink and source 10mA and

output latches with built in hysteresis, the

LT1712 simplifies the design of discrete

PWM circuits, current sensing circuits for

switching power supplies, bang-bang con-

trollers and a host of other applications.

The LT1712 is available in a 16-pin

SSOP package that occupies the same foot-

print as a conventional SO-8 package. The

part is specified for operation over the indus-

trial or the commercial temperature

ranges.

INPUT OVERDRIVE (mV)

PROPAGATION DELAY (ns)

3.5

4.0

4.5 t

PD+

PD–

30 50

1712 TA02

3.0 10 20 40

5.0

5.5

6.0

= 25°C

= 5V

–

= 0V

STEP

= 100mV

Figure 1. Propagation Delay

vs Input Overdrive

for use in a wide variety of low voltage

applications such as clock recovery or as a

line receiver in broadband communications

Linear Technology Chronicle

• January 2001

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.

Dual N-Channel High

Side Switch Controller in

SOT-23 Draws Just

A—LTC1982

The LTC1982 is a dual micropower

switch controller in a SOT-23 package. The

LTC1982 connects and disconnects loads

from a low voltage power source (Figure 1).

It incorporates a pair of charge pump triplers

to produce high side gate drive for logic

level N-channel MOSFETs.

The LTC1982 has an input voltage

range of 1.8V to 5V that permits using a

single Li-Ion or multiple NiCd, NiMH or

Figure 1. LTC1982 Dual Switch

Controller Uses N-Channel MOSFETs Figure 2. Direct Interface to 5V Logic

GATE 1 GATE 2

SHDN 1 SHDN 2GND

LTC1982 LOAD 1 LOAD 2

10µF

SHDN 1

SHDN 2

1.8V TO 5.0V

654

123

1982 TA01

1/2 Si6925DQ

GATE 1

SHDN 1 GND

1/2 LTC1982

3.3V

LOAD

1982 F02

3.3V

Si3442DV

alkaline batteries. Its quiescent current is just

10µA per gate and 1µA when in shutdown.

The LTC1982 is suited for space-restricted,

handheld applications such as cellular

phones, handheld computers and portable

point-of-sale terminals where shutting down

peripherals or subsystems that draw a high

quiescent current can greatly improve bat-

tery life. It is also useful in Hot Swap™

applications or where power sequencing

must be implemented in multipower

environments.

Complete circuits using the LTC1982

require only a pair of N-channel MOSFETs

and a single input capacitor. N-channel FETs

are available in small packages, such as a

SC-70, with a 0.1Ω RDS(ON), making pos-

sible a solution size of just 0.045in2

(29mm2). The FETs can be driven either

high side or low side. A discrete P-channel

approach requires a larger package device.

The LTC1982 has two separate shutdown

pins for independent load control.

Because the input ESD protection

diodes are referenced to the ground pin

instead of the supply pin, it is possible to

drive the LTC1982 inputs from 5V logic

even though the LTC1982 is powered from

a 3.3V supply, as shown in Figure 2. The

reverse situation is also true; the LTC1982

can be driven with 3V logic even when the

supply to the device is as high as 5V.

Comparator with Latch: 7ns, Rail-to-Rail Input

and Output—LT1713

The LT1713 is a single comparator that

features a propagation delay of only 7ns, a

rail-to-rail input voltage range, complemen-

tary rail-to-rail CMOS/TTL compatible out-

puts, an internal data latch and an operating

supply range of 2.4V to 12V. This unique

combination of features greatly expands the

variety of applications in which the LT1713

can be used.

The LT1713’s fast response and 2.4V

operation combined with its rail-to-rail

inputs and CMOS compatible outputs

makes it ideal for use in a wide variety of

low voltage digital applications such as

clock recovery or line receiver in broadband

communications systems. Additionally, the

LT1713’s 12V operational capability, low

(5mA/comparator) supply current and high

speed in a small MSOP package make it well

suited for use in automatic test equipment.

The internal latch makes it suitable for use in

data sampling circuits. With rail-to-rail

complementary outputs that can sink and

source 10mA and an output latch with built-

in hysteresis, the LT1713 simplifies the

design of discrete PWM circuits, current

sensing circuits for switching power

supplies, bang-bang controllers and a host of

other applications.

The LT1713 comes in an 8-pin MSOP

package and is pin compatible with the

LT1394 and LT1671. The LT1714 is a dual

version of the design.

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