A Showcase of Linear T echnology’ s Focus Products

Linear Technology Chronicle

December 1998 Vol. 7 No. 12

Product of the Month

LT1676/LT1776: Wide Input Range Step-Down Switching Regulators ................................... 2

LTC1627: High Efficiency 500mA Step-Down Switcher Operates from

1- or 2-Cell Li-Ion Batteries................................................................................................. 2

While Drawing Only 200

Linear Technology brings you the

industry’s smallest and easiest to use 24-bit

of 50Hz or 60Hz rejection without the need

for a precision crystal or external clock. The

LTC2400 is intended for DC measurements

scale error to meet the most demanding DC

50Hz or 60Hz is accomplished with a single

pin. Packaged in an 8-pin SO, the LTC2400

performing conversions and automatically

and while waiting for the next conversion

leled accuracy in a small, easy-to-use

It gets better. The LTC2400 uses a

unique 4th order sinc filter that settles in a

LTC2400 performs autocalibration of offset

and gain errors during each conversion trans-

parently to the user. No need to flush digital

filters and manage complicated status regis-

ters here. The converter operates on a

“convert command” and outputs a 24-bit

answer. The analog input range extends

12.5% below ground and above VREF while

still providing accurate results. This range

allows measurement of signals below

ground. The accuracy of the LTC2400

source applied to set a user-defined rejection

frequency and output rate. Communication

with the LTC2400 is accomplished over an

easy-to-use SPI compatible serial interface.

Applications for the LTC2400 will

benefit from the compact, easy-to-use

design. Such uses include DC voltage and

scales, temperature measurements, portable

handheld instrumentation and DC multi-

plexed data acquisition. The small size,

SO-8 package will allow next generation

designs to be realized with unprecedented

form factors and accuracy. A complete

LT1676/LT1776: Wide Input Range Step-Down Switching Regulators

For Automotive, “Fire Wire,” 48V Telecom and Cell Phone Chargers

switching regulators for high efficiency step-

down regulation from up to 60V inputs. The

circuits are pin-for-pin compatible and

virtually identical. The difference is their

500mA output current. The input voltage

ciency in the upper portion of this range

requires very fast output switch edge rates.

The LT1676/LT1776 contain specialized

circuitry to provide this performance. Other

circuitry monitors output load level and

reduces leading-edge switch rate when the

output load is light. This function helps

avoid pulse skipping at light loads and the

Along with true current mode opera-

tion, the LT1676/LT1776 include

microampere shutdown and undervoltage

ported. (See Linear Technology magazine,

The LT1776 is favored for its higher

switching frequency that allows for a smaller

means increased AC switching losses and

thus higher thermal dissipation, so that the

LT1676 may be preferred for many uses.

The LT1676 can operate continuously at

high loads at 60V while the LT1776 is

limited to 40V in a continuous high output

condition. Figure 1 shows a minimum com-

ponent count circuit using the LT1676. The

circuit produces 5V at up to 500mA output

unregulated 8V to 40V power, for battery

charging from a wide input range source,

and for step-down from the 48V rail in

telecom systems. LTC provides other 60V

input voltage range switching regulators and

controllers for output currents up to 50A.

down switching regulator that is optimized

for Li-Ion batteries in low voltage applica-

tions such as cellular phones and PDAs.

Burst Mode operation and built-in power

switches in an SO-8 package to offer the

most compact and efficient power manage-

ment solution for portable applications

operating from 1- or 2-cell lithium-ion

0.8V. Switching frequency of 350kHz

allows the use of small surface mount induc-

tors and capacitors. Efficiencies in excess of

90% over a wide range of output current and

100% duty cycle allow the user to extract the

maximum power available from the battery.

A precision 2.5V undervoltage lockout

prevents battery damage due to over-

discharge by shutting the LTC1627 down,

Linear Technology Chronicle •

December 1998

LTC1650: 16-Bit Voltage Output DAC Now Available for

5V Supply Systems

delivers true 16-bit monotonic performance

supplies. The buffered voltage output swings

rail-to-rail into 1000pF. The bipolar or

tions. The LTC1650 also features fast

current mode switching regulator designed

for SMBus control of CCFL (Cold Cathode

Fluorescent Lighting) displays. A wide input

1650 TA02

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

lower pull-up resistor values, but the addi-

tional current through the low value resistors

increases the low state bus voltage, decreas-

ing noise margins. Slow rise times can

pull-up designed to enhance data transmis-

sion speed and reliability under all specified

SMBus loading conditions. With the

LTC1694, the user can connect more devices

simplicity is offset by the relatively slow rise

times they afford when bus capacitance is

LTC1597: Ultra-Accurate 16-Bit DAC with On-Chip 4-Quadrant Resistors

ates from a single 5V supply. INL and DNL

amp offset has been greatly reduced com-

pared to previous generations of multiplying

offset will cause about 0.55LSB INL degra-

dation and 0.15LSB DNL degradation with a

put range is 0V to –10V and the DAC

reference input.

The device includes an internal

feature that permits the update of several

The parallel input of the LTC1597 is

advantageous for fast settling applications.

Used with the LT1468 high speed op amp,

the circuit’s settling time to 0.0015% with a

The LTC1597 is designed for applica-

tions such as process control and industrial

TO V