January 2000 - Linear Technology

Linear Technology Chronicle

• January 2000 1

Product of the Month

, LTC and LT are registered trademarks of Linear Technology

Corporation. Hot Swap and Burst Mode are trademarks of Linear

Technology Corporation.

A Showcase of Linear Technology’s Focus Products

Linear Technology Chronicle

January 2000 Vol. 9 No. 1

Inside This Issue:

A Dual, 200mA, 700MHz Op Amp in SO-8 for High Speed Digital Modems—LT1886 ........... 2

10-Bit Accurate Battery Current Monitor is Micropower, Tiny and Low Cost—LTC1197,

LTC1197L and LTC2050 ........................................................................................................ 3

Synchronous Boost DC/DC Converter Disconnects Output in Shutdown—LT1306............... 3

Isolated RS485 Transceiver Withstands 2500V

RMS

and Includes Isolated Power Driver—LTC1535 ...................................................................... 4

Dual Supply Hot Swap Controller Provides Simple

Power Supply Sequencing for Processor I/O and

Core Voltages—LTC1645

Continued on page 2

The LTC

1645 is a dual Hot Swap

controller and power sequencer that protects

boards with multiple supplies during live

insertion and removal. The LTC1645 oper-

ates with supply voltage combinations from

as low as 1.2V and 2.5V, up to traditional

3.3V/5V and 5V/12V applications. The

controlled turn-on from a single input

makes it ideal for the critical supply

sequencing requirements of microproces-

sors with multiple supplies. The LTC1645

is also able to properly sequence the power

supply between I/O and core voltages on

high-end microprocessors.

0.005Ω*IRF7413

IRF7413

0.005Ω

10Ω10Ω

10k

CLOAD2

CLOAD1

VOUT1

VOUT2

3.3V

623

1645 TA01

0.01µF

25V

0.01µF

25V

VIN2

VIN1

GND

PLUG-IN CARD

BACKPLANE

SENSE1 VCC2

GATE1 SENSE2 GATE2

LTC1645

(8-LEAD)

CONNECTOR 1

CONNECTOR 2

VCC1

The device is available in both SO-8

and S14 packages. The LTC1645xS8 (in

SO-8) is the smallest dual supply Hot Swap

controller and provides Hot Swap for two

voltages from a single “ON” input. It also

provides current sense for each supply using

external sense resistors. The LTC1645xS

(14-lead SO) adds the capability to monitor

the output voltages and generate a micropro-

cessor RESET signal for each as well as a

FAULT output which may be used to auto-

matically reset the circuit breaker after a

fault. Both the LTC1645xS8 (SO-8) and the

LTC1645xS (S14) are available for the com-

mercial and industrial temperature

ranges.

Figure 1. 5V and 3.3V Hot Swap

SOT-23 Low Voltage

Step-Down Switching

Regulator Has High

Efficiency and Low

Dropout—LTC1772

The LTC1772 DC/DC controller IC is

highly efficient over its entire load range

(Figure 1) and works down to a low 2.5V1

input voltage. The circuit can be very small,

less than 2cm2, as a result of its minimal size

external components and its tiny 6-lead

SOT-23 package. The LTC1772 circuit, with

its external MOSFET, will supply an output

current as high as 5A. Its wide input voltage

range of 2.5V to 9.8V makes it useful for

single Li-Ion cell and many multiple-cell

systems. It is also ideal for conversion of

3.xV sources to 2.xV and 1.xV outputs.

This constant operating frequency,

current mode switching regulator has

excellent line and load transient response.

Its 550kHz switching frequency makes for

tiny components, low noise and easy filter-

ing (Figure 2). Frequency foldback and

overvoltage functions protect the circuit

from mishaps such as overcurrent and large

transient conditions. The 0.8V reference

voltage is accurate within ±2.5% over tem-

perature, line and load variations.

Unique Features for High Efficiency and

Low Power

For systems with widely varying loads,

Burst Mode

operation is employed to

enhance low-current efficiency. The con-

verter achieves over 90% efficiency with

loads above 1A and yet maintains 80% effi-

ciency with loads as low as 1mA. The

P-channel MOSFET may be chosen to best

fit the system requirements.

Linear Technology Chronicle

• January 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.

A Dual, 200mA, 700MHz

Op Amp in SO-8 for High

Speed Digital

Modems—LT1886

The LT

1886 is a 200mA minimum

output current, 700MHz, dual op amp

designed for high speed digital modems.

Specifically tailored for G.Lite and G.DMT

“upstream” line driver applications, the

LT1886 provides low distortion power for

transmitting data from the home PC to the

central office.

The LT1886 provides the 13dBm of

low distortion power required by the G.Lite

and G.DMT specifications. The low –72dBc

of distortion of the LT1886 supports good

interoperability between the modem and any

of a variety of systems in use at the central

office. The LT1886 is gain-of-ten stable. A

simple RC network between the inputs can

be used to reduce the minimum stable gain

value if necessary.

With a maximum supply rating of

13.2V, the LT1886 can function from a 12V

±10% supply, readily available in the PC.

The output drives a 25Ω load to ±4.3V with

±6V supplies. On ±2.5V supplies the output

swings ±1.5V with a 100Ω load. The ampli-

fier is stable with a 100pF capacitive load,

making it useful in buffer and cable driver

applications.

The LT1886 features balanced, high

impedance inputs with 4µA maximum input

bias current and 4mV maximum input offset

voltage. Single supply applications are easy

to implement and the LT1886 has lower

total noise than current feedback amplifier

implementations.

The LT1886 is available in an SO-8

package. With a θJA of 80°C/W, the LT1886

can easily dissipate the required 500mW of

power required in G.Lite/G.DMT applica-

tions.

–

1/2 LT1886 12.4Ω

1:2*

12V

619Ω

32.4Ω

20k10k

IN–

IN+

10k 20k

1µF

1000pF

0.1µF

–

1/2 LT1886 12.4Ω1886 TA01

619Ω

100Ω

*MIDCOM50215

Figure 1. Single 12V Supply G.Lite Line Driver

LTC1772 from page 1

Figure 2. Tiny, High Efficiency Step-Down ConverterFigure 1. Efficiency vs Load Current

for the Circuit of Figure 2

The LTC1772 extends battery life with its

low quiescent current of 270µA and its

selectable shutdown mode (8µA supply).

An undervoltage lockout feature automati-

cally shuts down the LTC1772 when the

input falls below 2.0V.

The LTC1772 will deliver a regulated 2.5V

even as the voltage of the single Li-Ion cell

drops to 2.7V, its end-of-charge condition.

For low dropout voltage, the PWM duty

cycle of the circuit will increase to 100%,

at which point the MOSFET is held on con-

tinuously.

The device will function down to a 2.0V input but with

reduced output current below 2.5V.

LOAD CURRENT (mA)

EFFICIENCY (%)

100

1 100 1000 10000

1772 F01b

40 10

= 3.3V V

= 4.2V

= 8.4V

OUT

= 2.5V

SENSE

= 0.03Ω

= 9.8V

= 6V

/RUN

LTC1772

10k

0.03Ω

169k

78.7k

4.7µH

220pF

C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT

C2: SANYO POSCAP 6TPA47M

D1: IR10BQ015

L1: MURATA LQN6C-4R7

M1: Si3443DY

R1: DALE 0.25W

GND

1772 F01a

PGATE

SENSE

–

10µF

16V

2.5V

TO 9.8V

OUT

2.5V

47µF

Linear Technology Chronicle

• January 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

10-Bit Accurate Battery Current Monitor is Micropower,

Tiny and Low Cost—LTC1197, LTC1197L and LTC2050

The digital output battery current

monitor shown in Figure 1 is based upon

the LTC1197 10-bit analog-to-digital con-

verter plus the LTC2050 zero-drift op amp.

The LTC1197 is available in an 8-lead

MSOP package and the LTC2050 comes in

a 6-lead SOT-23. The LTC1197 operates

from 2.7V to 9V (12V absolute maximum)

supplies and features automatic shutdown

between conversions. Designed for use in

mixed-supply systems, the LTC1197 works

properly even when the processor voltage is

greater than or less than the ADC supply.

There are two versions of the LTC1197: the

LTC1197L is tested at 2.7V with specifica-

Figure 1. This 0A to 2A Battery Current Monitor Draws 30µA from a Battery

Continued on page 4

Synchronous Boost

DC/DC Converter

Disconnects Output in

Shutdown—LT1306

The LT1306 is a single chip synchro-

nous boost DC/DC converter that discon-

nects the load in shutdown and that controls

the input current during start-up. It will con-

tinue to regulate when the input voltage is

higher than the desired output.

Boost DC/DC converters generally lack

a true shutdown capability so that extra cir-

cuitry is required to reduce power consump-

tion in stand-by. The output is always

connected to the input through the inductor

and diode. The unique configuration of

switch and rectifier in the LT1306 discon-

nects the output from the input in shutdown

without additional components.

Buck-Boost with Single Small Inductor

The LT1306 is also unusual among

boost converters by its ability to regulate the

output when the input voltage exceeds the

output voltage, permitting buck/boost opera-

tion with a single small inductor. This is use-

ful for generating an output that is within the

range of the input source, such as when

generating a 5V output from a 4-cell alkaline

battery (Figure 1). Normally this capability

requires a SEPIC topology involving larger

magnetics. As a synchronous boost con-

verter, the LT1306 does not require a large

external rectifier diode, saving considerable

board space.

10µH

1µF

VIN CAP

LT1306

75k R2

249k

768k

15nF

CIN2

0.1µF

CERAMIC

CIN1

22µF

3.6V

TO 6.5V

22pF

CO2

1µF

CERAMIC

CIN1: AVX TAJC226M010

CO1: AVX TPSE227M010R0100

C1: AVX TAJA105K020

D1: MMBD914LT1

L1: CTX10-3

1306 F09

OUTS/S

VCGND

CO1

220µF

Figure 1. 4-Cell NiMH (or Single Cell Li-Ion) to 5V Output

tions guaranteed from 2.7V to 4V while the

LTC1197 is tested at 5V with specs guaran-

teed from 4V to 9V.

The LTC2050 is a new low power, low

cost, chopper-stabilized op amp available in

the SOT-23 package. The 6-lead version

includes shutdown. Its maximum offset

voltage is 3µV with a maximum drift of

30nV/°C. Noise is only 1.5µV

P-P

(0.1Hz to

10Hz). The LTC2050 operates over a 2.7V

to 6V supply range.

The system supply current is limited to

an average of 30µA by sampling the ADC

at 1Hz (Figure 2) and by using the

LTC2050 SHDN pin to turn on the op amp

5ms prior to making a measurement and

then turn it off after the measurement has

been made. The battery current is sensed

with the 0.005Ω resistor and amplified by

the LTC2050. The LTC1197 digitizes the

amplifier output and sends it to the micro-

processor in serial format. The LT1004

provides the full-scale reference for the

ADC. The circuit can be located near the

battery and data transmitted serially to the

microprocessor.

–

LTC2050

SHDN

240k 56k TO

µP

100Ω

0.005Ω

2A FULL

SCALE

500pF

2.7V

TO 6V

1µF

0.1µFLT1004-1.2

DN184 F03

+IN

–IN

GND

CLK

OUT

REF

LTC1197 OR

LTC1197L

SAMPLING FREQUENCY (kHz)

0.01

SUPPLY CURRENT (µA)

100

1000

10000

100

DN184 F01

0.1 0.1 110 1000

= 5V,

CLK

= 7.2MHz

= 2.7V,

CLK

= 3.5MHz

Figure 2. The LTC1197/LTC1197L Have

Reduced Supply Current Consumption

at Lower Sample Rates

Linear Technology Chronicle

• January 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.

Isolated RS485 Transceiver Withstands 2500V

RMS

and Includes Isolated Power Driver—LTC1535

n industrial environments where high

voltage ground shifts occur, the data bus

must be isolated from the logic circuitry.

The new LTC1535 isolated RS485 trans-

ceiver from Linear Technology can with-

stand up to 2500V

RMS

of ground potential

difference. The LTC1535 uses a capacitive

isolation barrier between the logic and the

RS485 transceiver. No additional power

supplies are needed since the powered side

drives a transformer supplying the isolated

side of the transceiver.

In addition to the 2500V

RMS

isolation,

the LTC1535 full-duplex transceiver

includes several features that make it well

suited for industrial environments. The

driver outputs and receiver inputs are pro-

tected to 8kV ESD levels, eliminating the

need for external protection. The outputs

are short-circuit current limited and have a

selectable slew rate to minimize EMI or

reflections. The high impedance receiver

inputs of the LTC1535 support up to 128

nodes and include a fail-safe feature that

guarantees a high receiver output level for

open or shorted inputs. The LTC1535

makes isolated RS485 easy and eliminates

the need for optos. The LTC1535 is avail-

able in an isolated 28-lead SO package for

the commercial temperature range.

SLO

RO2

1535 TA01

GND

400kHz

1411

GND2

1/2 BAT54C

CC2

ST1 ST2

10µF

TWISTED-PAIR

CABLE

Figure 1. Isolated RS485 Transceiver

LT1306 from page 3

Inrush and Short-Circuit Protection

A third unique feature of the LT1306 is

its ability to limit inrush current, such as

when a newly inserted battery charges the

output capacitor. In conventional boost con-

verters, a high input-transient current spike

invariably results during start-up. In the

LT1306 design, the inductor voltage reverses

polarity every switching cycle. This, along

with cycle-by-cycle current limit, eliminates

the inrush current spike.

The LT1306 is a current mode PWM

switching regulator that operates at a con-

stant frequency of 340kHz. The device may

be synchronized to an external clock

between 425kHz and 500kHz. Built-in

Burst Mode operation maintains high effi-

ciency at light loads (Figure 2). The LT1306

has a no-load quiescent current of 160µA

while consuming just 9µA in shutdown. The

device is packaged in a thermally-enhanced,

SO-8 to allow a very small system size. It

operates from inputs of 1.8V up to 10V. Its

internal switches are rated at two amps and

0.25Ω.

The LT1306 is a simple, clean solution

for generating a 1A output from a single

Li-Ion cell or from 2-, 3- or 4-battery cells,

for compact systems such as portable bar-

code readers, PDAs, cell phones, handheld

instruments and local 3.3V to 5V conver-

sion.

LOAD CURRENT (mA)

EFFICIENCY (%)

10 100 1000 2000

1306 F10a

= 4.8V

= 3.6V

= 6V

= 5V

L1 = 10µH

Figure 2. Efficiency of the Circuit

in Figure 1

Linear Technology Products

Are Distributed By:

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