January 1997 - Linear Technology

Linear Technology Chronicle •

January 1997

A Showcase of Linear Technology’s Focus Products

Linear Technology Chronicle

January 1997 Vol. 6 No. 1

Products of the Month

Constant Frequency DC/DC Converters Offer

High Efficiency at Light Loads

, LTC and LT are registered trademarks of Linear Technology Corporation.

Inside This Issue:

The LTC

1433/LTC1434 are low

noise, current mode, step-down DC/DC con-

verters that are capable of supplying up to

450mA of output current at 3.3V with up to

93% efficiency. Quiescent current is only

470µA and in shutdown mode, the devices

draw only 15µA. Input voltage range is 3.5V

to 13.5V and output voltage accuracy is

±2.4%. Both devices operate at a fixed fre-

quency with the LTC1434 phase lockable to

an external clock signal for frequency-

sensitive applications. Both devices are

packaged in narrow SSOPs. These DC/DC

converters are excellent for portable telecom

applications which must minimize noise and

RFI in sensitive IF bands.

The LTC1433/LTC1434 incorporate

two internal P-channel MOSFETs, with a

parallel combined resistance of only 0.6Ω.

low output currents, as shown in Figure 1.

Efficiency at low output current is typically

improved 3% to 5% over other fixed fre-

quency devices. The output voltage is pin

selectable to 3.3V, 5V or adjustable with two

external feedback resistors (see Figure 2). A

power-on reset is included and generates a

signal delayed by 65,536/fCLK after the out-

put is within 5% regulation. The LTC1433/

LTC1434 are offered in 16-lead and 20-lead

narrow SSOP packages, respectively.

Contact your local Linear Technology sales

office for a data sheet and evaluation

samples. For further information, visit our

web site at www.linear-tech.com.

1

2

3

4

5

6

7

16

15

14

13

12

11

10

SSW

NC

BSW

NC

SGND

RUN/SS

LBO

LBI

PWRV

IN



OSC



POR



OSENSE



PROG

LTC1433

PGND

68µF**

20V

0.1µF

100µF*

10V

D1:MOTOROLA MBRS130LT3

L1: COILCRAFT D03316-104

 

OUT



3.3V

L1

100µH

POWER-ON

RESET

IN

3.5V TO 12V

680pF

5.1k

10k

6800pF

47pF

1433/34 F01

* AVX TPSD107M010R0100

** AVX TPSE686M020R0150

The Adaptive Power

output stages selec-

tively drive one or both of the switches at

frequencies up to 700kHz to reduce switch-

ing losses and maintain high efficiencies at

Figure 1. The LTC1433 Provides Up to

93% Efficiency at 3.3V Output

LOAD CURRENT (A)

0.001

EFFICIENCY (%)

0.01 0.1 1

1433/34 TA01

100

90 V

= 5V

= 12V

= 9V

Figure 2. LTC1433 High Efficiency Step-Down Converter Maximizes Battery Life

Adaptive Power is a trademark of Linear Technology Corporation.

UltraFast Linear

Regulator Eliminates

Bulky Output Capacitors

The LT

1575/LT1577 are single and

dual low dropout linear regulator controller

ICs that deliver UltraFast

transient

response with ±1% regulation. The fast load

transient response, shown in Figure 1, elimi-

nates the need for expensive tantalum or

electrolytic bulk output capacitors required

by traditional solutions. They drive an exter-

nal N-channel MOSFET as a source follower

and supply up to 15A output current. Output

voltage tolerance is ±0.6% at 25°C and ±1%

over temperature. Selection of the N-channel

MOSFET RDS(ON) allows user-settable

dropout voltage performance and output cur-

rent. The LT1575/LT1577 are targeted at

VRE Pentium

microprocessor

motherboards and other high speed boards

that require very accurate, very high speed

regulator circuits.

The LT1575/LT1577 incorporate a high

side current limit amplifier that activates a

fault protection timer circuit. A multifunc-

tion Shutdown pin (Figure 2) provides either

1MHz Continuous Time Lowpass Elliptic Filter Delivers

72dB SNR in SO-8 Package ................................................................................................... 2

Fast Current Feedback Amplifiers Tame Low Impedance CCD Loads .................................. 3

Precision 10MHz Rail-to-Rail Dual and Quad Op Amps Draw Less Than 1.7mA/Amplifier.... 4

http://www.linear-tech.com, Check It Out! ................................................................................4

Continued on page 2

UltraFast is a trademark of Linear Technology Corporation.

Pentium is a registered trademark of Intel Corporation.

www.linear-tech.com

Linear Technology Chronicle •

January 1997

LT1575 from page 1

decoupling capacitors at the microprocessor

socket—a network that typically consists of

10 to 24 inexpensive surface mount 1µF

capacitors, depending on the particular pro-

cessor being used.

The LT1575 is offered in 8-pin PDIP

and SO packages and the LT1577 is offered

in a 16-pin narrow SO package. They are

available in precision-trimmed adjustable

and fixed output voltage versions, specifi-

cally at 1.5V, 2.8V, 3.3V, 3.5V and 5.0V.

All devices are available from stock. Contact

your local Linear Technology sales office for

a data sheet and evaluation samples. For fur-

ther information, visit our web site at

www.linear-tech.com.

current limit time-out, overvoltage protec-

tion, thermal shutdown or a combination of

these functions. Precision-trimmed fixed and

adjustable output voltage versions accommo-

date any required microprocessor power

supply voltage. The only output capacitors

required are the high frequency ceramic

50mV/DIV

2A/DIV

1575/77 TA02

100µs/DIV

Figure 1. The LTC1575’s Fast Transient

Response Eliminates the Need for Expensive

Tantalum and Electrolytic Output Capacitors Figure 2. LTC1575-3.3 Provides 3.3V with 1%

Output Tolerance at 5A

1MHz Continuous Time

Lowpass Elliptic Filter

Delivers 72dB SNR in

SO-8 Package

The LTC1560-1 is a 5th order, continu-

ous time, elliptic lowpass filter in an SO-8

package, representing the industry’s first

monolithic high frequency filter. Before the

LTC1560-1, this filter solution was only

realized with discrete components that many

times needed to be “hand” tuned to achieve

consistent filter response. Now, the

suited for ADSL, HDSL and other wide

bandwidth communication systems. The

LTC1560-1 will also fit demanding alias

filter requirements in high speed data acqui-

sition systems.

The LTC1560-1 operates with ±5V

supplies and has a power savings mode that

reduces supply current from 22mA to less

than 1mA. It is immediately available in vol-

ume from stock in an SO-8 surface mount

package. Call your local Linear Technology

sales office for a data sheet and evaluation

samples. For additional information, visit

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

LTC1560-1 delivers solid-state high fre-

quency filter performance, greatly improving

part-to-part reliability and filter response

tolerances.

The LTC1560-1 offers significant

dynamic range improvements over existing

solutions. SNR is 69dB and THD is –62dB

with a 1VRMS input signal. SNR can be

improved to 75dB using a 2.1VRMS input. It

has a flat passband to 0.55fC with a typical

ripple of only ±0.2dB. As shown in Figure

1, the stopband attenuation is better than

60dB up to 10MHz. The LTC1560-1 is pin

selectable for cutoff frequencies of 500kHz

and 1MHz (see Figure 2) and is ideally

Figure 2. The LTC1560-1 Has Pin Selectable

Cutoff Frequencies at 500kHz and 1MHz

GND

–

GND

OUT

SHDN

0.5f

LTC1560-1

(OR –5V)

0.01µF

0.1µF

–5V

1560-1 TA01

0.01µF

–5V

1MHz

5V

500kHz

Figure 1. Frequency Response of the

LTC1560-1 Elliptic Lowpass Filter

FREQUENCY (MHz)

0.1

–90

GAIN (dB)

–70

–50

–30

–10

110

1560-1 TA02

–80

–60

–40

–20

CUTOFF

= 1MHz/500kHz

1

2

3

8

7

6

5



SHDN



GND

OUT

IPOS

INEG

GATE

COMP

C2

1µF

C5

220µF

1575/77 TA01

OUT



3.3V

R2

5Ω

R1

7.5k

12V

(CONTROL POWER)

LT1575-3.3

C4

1000pF

Q1

IRFZ24

C3

10pF

C6

1µF

×24

Linear Technology Chronicle •

January 1997

Application of the Month

Fast Current Feedback Amplifiers Tame Low Impedance CCD Loads

A good example of a difficult capacitive

load is a clock driver for charge-coupled

devices (CCD). These devices require pre-

cise multiphase clock signals to initiate the

transfer of light-generated pixel charge from

one charge reservoir to the next. Noise, ring-

ing or overshoot on the clock signal must be

avoided. Two problems complicate clock

generation. First, CCDs present an input

capacitance (typically 100pF to 3300pF)

which is directly proportional to the number

of sensing elements (pixels). Second, CCDs

often require the clock’s amplitude to exceed

The LT1206, LT1207 and LT1210 are

fast current feedback amplifiers capable of

delivering high levels of current. They can

be readily compensated for reactive loads

and are fully protected against thermal and

short-circuit faults. Table 1 summarizes

their electrical characteristics.

The devices in Table 1 combine the

high output current required to slew large

capacitances with appropriate frequency

compensation. All of the CFAs described

here are C-Load

amplifiers and are stable

with capacitive loads up to 10,000pF.

the logic supply. The amplifying filter in

Figure 1 addresses these issues. Both CFAs

in the LT1207 are configured for a 3rd

order Gaussian lowpass response with

1.6MHz cutoff frequency (one section is

shown). This transfer function produces

clean clock signals with controlled rise and

fall times. Figure 2 shows the LT1207’s

quadrature outputs driving two 3300pF

loads that simulate a CCD image sensor.

Ringing and overshoot are notably absent

from the clock signals, which have rise and

fall times of approximately 300ns.

Figure 2. CCD Clock Driver Waveforms

QUADRATURE

INPUTS

FILTERED

CLOCK

OUTPUTS

Figure 1. CCD Clock Driver Uses LT1207 for 3rd Order Gaussian Lowpass Response

–

1/2

LT1207

1,16

SIMULATED

CCD ARRAY

LOAD

500kHz

2MHz

1k 3

–10V

10µF

20V

0.1µF

45pF

0.1µF0.1µF

15 C

510k

3300pF

91pF

DN132 F03

180pF

CLK

9QUADRATURE

OUTPUT TO

OTHER SECTION

74HC74

1CK

2CK

Table 1. Fast Current Feedback Amplifier Specifications

Rated Thermal Supply Low

Part Number Bandwidth Output Supply Slew Rate Resistance Current Power Op/

Number of CFAs (MHz) Current (A) Range (V) (V/µs) (Note 1) θ

(°C/W) (Note 2) (mA) Shutdown

LT1206 1 60 0.25 ±5 to ±15 I

LIM

LOAD

DD = 25, PDIP = 100 20 Yes

to 900 SO = 60, TO-220 = 5

LT1207 2 60 0.25 ±5 to ±15 I

LIM

LOAD

SO = 40 2 × 20 Yes

to 900

LT1210 1 35 1 ±5 to ±15 I

LIM

LOAD

DD = 25, SO = 40 30 Yes

to 1000 TO-220 = 5

Note 1: Slew rate depends on circuit configuration and capacitive load.

Note 2: θ

on SO packages measured with part mounted to a 2.5mm thick FR4 2oz copper PC board with 5000mm

area.

C-Load is a trademark of Linear Technology Corporation.

Linear Technology Chronicle •

January 1997

We would appreciate any comments

and suggestions you may have on our web

site. Please fax any comments to our web

administrator.

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

Precision 10MHz Rail-to-

Rail Dual and Quad Op

Amps Draw Less Than

1.7mA/Amplifier

The LT1498/LT1499 are dual and quad

precision op amps, representing the latest

addition to LTC’s growing family of C-Load

amplifiers. They draw only 1.7mA of supply

current per amplifier and cover a full rail-to-

rail common mode input range while driving

up to 10,000pF of load capacitance without

oscillation. A gain-bandwidth product of

10MHz and a slew rate of 5V/µs makes them

well-suited for a variety of applications.

They have the low voltage, low supply cur-

rent operation to work in portable

applications, yet offer the bandwidth and

slew rate to perform signal processing func-

tions beyond the ability of many other

precision rail-to-rail devices.

The LT1498/LT1499 are true rail-to-rail

devices and can operate over a total supply

voltage of 2.2V to ±15V. Maximum offset

voltage is 475µV, while maximum input bias

current and input offset current are 500nA

and 50nA, respectively. Figure 1 shows the

LT1498 in a typical active filter application

with the frequency response in Figure 2.

The LT1498 is available in 8-pin PDIP

and SO packages and the quad LT1499 is

offered in the 14-pin SO package. Both are

immediately available in volume from stock.

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.

FREQUENCY (Hz)

100

GAIN (dB)

–50

–30

–10

1498 TA02

–70

–90

–60

–40

–20

–80

–100

–110 1k 10k 100k 10M

= 2.7V

P-P

= 3V

http://www.linear-tech.com, Check It Out!

LinearView, Micropower SwitcherCAD and SwitcherCAD are

trademarks of Linear Technology Corporation. America Online

is a service mark of America Online, Inc. Microsoft is a regis-

tered trademark of Microsoft Corporation. Internet Explorer is a

trademark of Microsoft Corporation. Netscape Navigator is a

trademark of Netscape Communications Corporation. Adobe

and Acrobat are registered trademarks of Adobe Systems Incor-

porated. ViewFirst is a trademark of NanoSpace, Inc.

Linear Technology has an internet web

site to assist you in receiving the very latest

information on our products and services on

a timely and efficient basis. The address is

http://www.linear-tech.com.

You can access this web site via a

dedicated Internet Service Provider (ISP) or

by using a gateway provided by an online

service provider, such as America Online

If you are using an ISP, the site is best

viewed with Microsoft

Internet Explorer

3.0 or Netscape Navigator

3.0. The site

also uses the Adobe

Acrobat

Viewer to

view downloaded documents. If you have

installed our LinearView

CD-ROM, then

you already have the viewer. If not, Acrobat

Viewer is available free for downloading

from the web site.

The site, linear-tech.com, includes all

LTC data sheets, application notes, design

notes as well as current and back issues of

Linear Technology magazine and Linear

Technology Chronicle. These items can eas-

ily be located using the handy site map,

accessible from the home page.

On the home page is QuickSearch, a

search engine that allows you to find a docu-

ment such as a data sheet, design note, etc.

by simply entering in a keyword or part

number. To save time, ViewFirst

allows

you to preview just the first page of a docu-

ment, prior to downloading the full .pdf file.

At the bottom of the preview page is the

option to download the entire file or to

request a FAX back. The FAX function is

currently available in North America,

Europe, Asia and Japan.

CAD software may also be downloaded

for your use, such as Micropower

SwitcherCAD

, SwitcherCAD

FilterCAD, Noise Disk and Spice Models.

Figure 2. Frequency Response of the

LT1498 Dual Op Amp Configured as a

100kHz Lowpass Filter

–

1/2 LT1498

6.81k

OUT

1498 TA01

330pF

11.3k

6.81k

–

1/2 LT1498

5.23k 47pF

1000pF

10.2k

5.23k

100pF

Figure 1. LT1498 Dual Op Amp as Single Supply

4th Order Butterworth Filter