September 1997 - Linear Technology

Linear Technology Chronicle •

September 1997

A Showcase of Linear Technology’s Focus Products

Linear Technology Chronicle

September 1997 Vol. 6 No. 9

Product of the Month

DC/DC Step-Up Controller Meets High Power Demands ........................................................ 2

SIM Power Supply and Level Translator Compatible with 3V and 5V Cards ........................... 2

3.3V Powered Barometric Pressure Signal Conditioner .......................................................... 3

2.5V Micropower Shunt Reference in SO-8 Guarantees 25ppm/°C and

0.05% Initial Accuracy .........................................................................................................3

Fixed Voltage Output Step-Down Converters Draw Only 10µA in Standby............................. 4 , LTC and LT are registered trademarks of Linear Technology

Corporation.

Dual Current Feedback Amplifier Delivers 125mA

Output Current and 900V/

s Slew Rate

MAX

SHDN

SS COMP

GND

SENSE

SHUTDOWNNC

NC 1000pF

OUT

3.3V

AT 500mA

EXT

: AVX TPSC226M016R0375

OUT

: AVX TAJC476M010

EXT

: COILTRONICS CTX50-1P

1504 • TA01

LTC1504-3.3

Figure 1. LTC1504 in Synchronous Buck

Architecture Operates over a 4V to 10V

Input Voltage Range and Requires Only

Four External Components

The LTC1504 has an internal 1% refer-

ence combined with a sophisticated voltage

feedback loop that provides optimum output

voltage accuracy and fast load transient

response and requires no current sense

resistor. Synchronous operation allows it to

sink or source current for use in an active

Continued on page 4

Inside This Issue:

The LTC

1504 is a high efficiency

synchronous buck switching regulator for

use as a board-level 5V to 3.3V converter in

mixed voltage systems. A pair of on-chip

1.3Ω power switches enable it to supply an

output current of up to 500mA. Its 200kHz

operating frequency and fast transient

response reduce the number of output

capacitors required for most applications.

Peak efficiency of 92% is possible. The

LTC1504 is ideal in space limited designs

requiring localized voltage regulation, such

as in SCSI-II termination supplies, I/O sup-

ply for split-plane CPUs and as a supply for

low power digital signal processors.

Synchronous Buck

Switching Regulator in

SO-8 Offers High Output

Accuracy

The LT

1497 is a dual Current Feed-

back Amplifier (CFA) that features a 900V/

µs slew rate, 50MHz gain-bandwidth and a

guaranteed 125mA minimum output current

over temperature using ±15V supplies.

Maximum supply current per amplifier is

only 9mA for ±15V operation and just 7mA

for ±5V operation. High output drive and

slew rate combine to provide low distortion

transmission of either analog or digital infor-

mation down long distances of twisted pair,

shielded coax or other transmission media.

The LT1497 is shown below as an

HDSL line driver in just one of the many

line driving applications it performs. Any

application that requires delivery of a fast

signal into a low impedance load, such as

ISDN or video distribution, can benefit from

the LT1497. The LT1497 can drive a twisted

pair with a 1MHz, ±40mA peak signal at

–70dBc. Settling time for a 5V step input for

the LT1497 is just 55ns.

The LT1497 is offered in a low thermal

resistance SO-8 package (θJA = 80°C/W) for

operation with ±5V supplies and an

enhanced 16-pin SO (θJA = 40°C/W) pack-

age for operation with ±15V supplies.

Thermal shutdown protects against excessive

internal (junction) temperatures by cycling

between normal operation and an off-state.

For a data sheet and evaluation samples, con-

tact your local Linear Technology sales

office or for more information, visit our web

site at www.linear-tech.com.

–

560Ω

68.1Ω

1:1*

135Ω

560Ω

1/2 LT1497

*MIDCOM 671-7807

1497 TA01

Figure 1. HDSL Line Driver Has Thermal and Current Limit Circuits

that Protect Against Fault Conditions

Linear Technology Chronicle •

September 1997

DC/DC Step-Up Controller Meets High Power Demands

The LT1680 is a high power current

mode step-up switching regulator controller

that drives N-channel MOSFETs with a

source voltage up to 60V and gate capaci-

tance up to 10,000pF. Its high power

capability makes it ideal for high voltage,

high current step-up applications (Figure 1)

that require hundreds of watts of output

power at very high efficiency (Figure 2).

PWM operating frequency is programmable

and can be synchronized up to 200kHz to an

external system clock for lower EMI. The

LT1680 is ideal as a switcher in the high

power industrial/automotive and telecom

areas.

The LT1680 incorporates program-

mable average current limiting allowing

accurate limiting of DC current in the mag-

netics, independent of ripple current. User

adjustable slope compensation provides

stable operation at duty cycles up to 90%. Its

current sense common mode range up to

60V allows current sensing to be referenced

to the input supply, eliminating the need for

sense blanking circuits. Its 5V reference

with 10mA sourcing capability provides a

local 5V supply for micropower ancillary

circuits.

The LT1680 is available in 16-lead

PDIP or wide SO packages over the com-

mercial and industrial temperature ranges.

For a data sheet and evaluation samples,

contact your local Linear Technology sales

office or for more information, visit our web

site at www.linear-tech.com .

SIM Power Supply and Level Translator Compatible with 3V and 5V Cards

1

2

3

4

5

6

7

16

15

14

13

12

11

10

SL/ADJ



AVG



SS



SGND



REF



SYNC

12V



GATE

PGND

RUN/SHDN

SENSE

–



SENSE

LT1680

R1

15k

R7

R2, 4.7k

C1

1nF

C3, 2.2nF

C5, 4.7nF

C4, 0.22µF

C2

1µF

C11, 1nF

1680 TA01

C6

0.1µF

R6

75k

R9

100k

C12

1µFM1

IRFZ44

×3

D1

MBR20100CT

×2



680µF

25V

×4

OUT



680µF

63V

×3

OUT



48V

5.2A

L1

25µH

SENSE



0.005Ω

12V



10V TO 15V

24A (DC)

L1: Kool Mµ

, 18T #14 ON 77314-A7

1

2

3

4

5

6

7

16

15

14

13

12

11

10

CIN

RIN

DATA

DDRV



SS

M1

CLK

RST

I/O



5V ±5%

VCC

≤ 10mA



GND

CLK

RST

I/O



–



GND

0.1µF10µF

LTC1555

3V GSM

CONTROLLER SIM



2.7V TO 10V

10µF

1555/56 TA01

OUTPUT POWER (W)

EFFICIENCY (%)

100

200

1680 TA02

75 50 100 150 250

OUT

= 48V

Figure 1. The LT1680 as a Step-Up Converter Generates

High Current 48V Bus Voltages Figure 2. Efficiencies Approach 95% in

12V to 48V Boost Applications

The LTC1555/ LTC1556 are integrated

solutions providing the power conversion,

digital signal level-shifting and 10kV ESD

protection needed for 3V or 5V GSM cellu-

lar telephone SIMs (Subscriber Identity

Modules). This permits new phones to main-

tain compatibility with older 5V SIM cards

as well as the newer 3V versions. The

LTC1555/LTC1556 have a step-up/step-

down charge pump that delivers a regulated

5V to the SIM card. Output voltage can also

be programmed to 3V, 5V or be directly

connected to the VIN pin—useful when

VIN = 3V to pass through the SIM card sup-

ply voltage. The input voltage to these

devices may range from 2.7V to 10V, per-

mitting a direct connection to the battery.

The LTC1555’s output current is 10mA

when VIN ≥ 2.7V and 20mA when

VIN ≥ 3V. It is short-circuit protected and in

addition has a soft start feature to control

inrush current at turn-on and tolerates indefi-

nite short-circuit conditions. The switched-

capacitor charge pump operates at a switch-

ing frequency of 650kHz. All SIM contact

pins on the LTC1555/LTC1556 are ESD

protected to 10kV—essential during inser-

tion and removal of the SIM card in normal

use.

The LTC1556 includes all of the fea-

tures of the LTC1555 plus an internal 4.3V

low dropout linear regulator with 5mA to

10mA output current capability. The

LTC1555 is available in a 16-lead narrow

SSOP package and the LTC1556 in a 20-

lead narrow SSOP package. Contact your

local Linear Technology sales office for a

data sheet and evaluation samples or visit

our web site at www.linear-tech.com for

more information.

Figure 1. LTC1555 in the GSM Cellular Phone SIM Interface

Kool Mµ is a registered trademark of Magnetics, Inc.

Linear Technology Chronicle •

September 1997

Application of the Month

3.3V Powered Barometric Pressure Signal Conditioner

The move to 3.3V digital supply volt-

age creates problems for analog signal

conditioning. In particular, transducer-

based circuits often require higher voltage

for proper transducer excitation. DC/DC

converters in standard configurations can

address this issue but increase power con-

sumption. Figure 1 shows a way to provide

proper transducer excitation for a baromet-

ric pressure sensor while minimizing power

requirements.

The 6kΩ transducer T1 requires pre-

cisely 1.5mA of excitation, necessitating a

relatively high voltage drive. A1 senses

T1’s current by monitoring the voltage drop

across the resistor string in T1’s return path.

A1’s output biases the LT1172 switch-

ing regulator’s operating point, producing a

stepped-up DC voltage which appears as

T1’s drive and A2’s supply voltage. T1’s

return current out of Pin 6 closes a loop

back at A1 which is slaved to the 1.2V ref-

erence. This arrangement provides the

required high voltage drive (≈10V) while

minimizing power consumption. This is so

because the switching regulator produces

only enough voltage to satisfy T1’s current

requirements. Instrumentation amplifiers

A2 and A3 provide gain and the LTC1287

A/D converter gives a 12-bit digital output.

A2 is bootstrapped off the transducer sup-

ply, enabling it to accept T1’s common

mode voltage. Circuit current consumption

is about 14mA. If the shutdown pin is

driven high, the switching regulator turns

off, reducing total power consumption to

about 1mA. In shutdown the 3.3V powered

A/D’s output data remains valid. In prac-

tice, the circuit provides a 12-bit

representation of ambient barometric pres-

sure after calibration. To calibrate, adjust

Figure 1. 3.3V Powered, Digital Output, Barometric Pressure Signal Conditioner

10k*

100k

1M

CALIB

1µF

22µF

1µF

0.05µF

2.2µF

700Ω*

100Ω**

10k

50Ω

BRIDGE

CURRENT

TRIM

BRIDGE

CURRENT

MONITOR

(0.1500V)

100k

3.3V

* = 1% FILM RESISTOR

** = 0.1% FILM RESISTOR

L1 = TOKO 262-LYF-0095K

T1 = NOVASENSOR

(FREMONT, CA)

NPH-8-100AH

LT1034

1.2V

1N4148

SHUTDOWN

L1

150µH

MUR110

1N752

5.6V

–

A2

LT1101



A = 10

≈ 10V DURING OPERATION

T1

PRESSURE

TRANSDUCER

–

A3

1/2

LT1078



–

A1

1/2

LT1078



CS CLK D

OUT

TO PROCESSOR

REF

GND

+IN

–IN

LTC1287

2N3904

GND

E2E1

LT1172

the “bridge current trim” for exactly 0.1500V

at the indicated point. This sets T1’s current

to the manufacturers specified point. Next,

adjust A3’s trim so that the digital output cor-

responds to the known ambient barometric

pressure. If a pressure standard is not avail-

able, the transducer is supplied with

individual calibration data, permitting circuit

calibration.

The LT1634-2.5 is a precision 2.5V out-

put shunt reference with an initial accuracy

of 0.05% and a maximum guaranteed drift of

25ppm/°C. The initial release in this family, a

1.2V output device, was introduced in the

August issue of Chronicle. The LT1634 is

stable with any value of output capacitor,

including none, saving components and

board space. These features make it an excel-

lent reference for use in portable meters,

precision regulators and in data conversion

applications. Advances in design, processing

and packaging techniques guarantee an oper- Figure 1. LT1634-2.5 Reference Has Low

Drift over a Wide Temperature Range

TEMPERATURE (°C)

–40

REVERSE VOLTAGE CHANGE (mV)

1634-2.5 TA02

–2

–20 20

–3

–4

–1

40 60 80 100

IR = 10µA

ating current of only 10µA and low tem-

perature cycling hysteresis. The compact-

ness of the product makes it ideal for space

limited applications.

The LT1634-2.5 is immediately avail-

able in volume from stock in 8-lead SO or

MSOP surface mount packages. Contact

your local Linear Technology sales office

for a data sheet and evaluation samples.

Visit our web site at www.linear-tech.com

for more information.

2.5V Micropower Shunt Reference in SO-8

Guarantees 25ppm/

C and 0.05% Initial Accuracy

Linear Technology Chronicle •

September 1997

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

Linear Technology

Products Are

Distributed By:

Almac/Arrow

Arrow/Schweber

Arrow/Zeus

Digi-Key

Electrosonic

Gerber Electronics

Farnell Electronics

Marshall Industries

Phase 1

Fixed Voltage Output Step-Down Converters Draw

Only 10

A in Standby

Fixed 3.3V and 5V output voltage

versions of the LTC1474/LTC1475

micropower converters are now available in

8-lead MSOP and SO packages. These high

efficiency (up to 92%) step-down DC/DC

converters draw only 10µA of standby cur-

rent while regulating the output voltage.

They have an on-chip power switch with

programmable peak current control to

maximize the life of alkaline batteries for

loads ranging from 1mA to 300mA. These

features permit a minimum area solution

ideally suited for battery-powered, handheld

products.

The LTC1474-3.3/ LTC1474-5/

LTC1475-3.3/LTC1475-5 operate over a

wide input voltage range of 3V to 18V (20V

Absolute Maximum). They have an adjust-

able output voltage and are short-circuit

protected. Their 100% duty cycle capability

ensures low dropout operation and allows

maximum energy to be extracted from the

batteries. Burst Mode

operation maintains

high efficiency over a wide range of load

currents. A low-battery comparator is

included and is functional during shutdown.

The LTC1475 is identical to the

LTC1474 except that it has a push-button

ON/OFF operation. Momentarily pushing

the ON button pin latches the LTC1475 on

and pushing the OFF button pin turns it off

(shutdown to 6µA IQ). This user interface

permits two-button operation without the

need for an external microcontroller or one-

LOAD CURRENT (mA)

EFFICIENCY (%)

100



90



80



70



60



0.03 3 300

1474/75 TA01

0.3 30

= 5V

= 10V

= 15V

L = 100µH

OUT

= 3.3V

SENSE

= 0Ω

GND

SENSE

LBI

RUN

OUT

LBO

LTC1474-3.3

100k

LOW BATTERY IN

RUN SHDN

0.1µF

10µF

25V



4V TO 18V

LOW BATTERY OUT

1474/75 FIX F01

L1

100µH

D1

MBR0530

100µF

6.3V

OUT

3.3V AT 300mA

L1 = SUMIDA CDRH74

Figure 1. The LTC1474-3.3 High Efficiency Step-Down Converter

Operates over a 4V to 18V Input Range

Figure 2. LTC1504 Self-Contained

Switching Regulator Offers Up to 92%

Peak Efficiency over a Wide Range of

Load Current

LOAD CURRENT (mA)

EFFICIENCY (%)

100

90

80

70

60

50

40

30

20

10

0100 500

1504 • TA02

LTC1504 from page 1

termination. An adjustable current limit cir-

cuit provides protection from overloads. The

LTC1504 fills the need for a low cost 5V to

3.3V switching regulator where high effi-

ciency at light load currents is not critical.

The LTC1504 is available in adjustable

and fixed 3.3V output versions—the latter

(LTC1504-3.3) uses an internal resistor pair

for improved space efficiency. Both devices

are offered in an 8-lead SO surface mount

package. Contact your local Linear

Technology sales office for a data sheet and

evaluation samples. Visit our web site

at www.linear-tech.com for more

information.

button operation with a microcontroller,

greatly simplifying ON/OFF control of

handheld products.

The LTC1474/LTC1475 are immedi-

ately available in 8-lead MSOP and SO

packages and are screened over both the

commercial and industrial temperature

ranges. Contact your local Linear

Technology sales office for a data sheet and

evaluation samples. Visit our web site at

www.linear-tech.com for more information.

Figure 2. Efficiencies over 92% Are

Possible for Various Load Currents

Burst Mode is a trademark of Linear Technology Corporation.