February 2001 - Linear Technology

Linear Technology Chronicle

• February 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 OPTI-LOOP are trademarks of

Linear Technology Corporation.

Linear Technology Chronicle

February 2001 Vol. 10 No. 2

Inside This Issue:

Fast Settling, True 16-Bit Voltage Output DAC Includes

Precision 4-Quadrant Resistors On-Chip—LTC1821 ............................................................. 2

FET Input, Fast, High Gain Photodiode Amplifier Using the LT1806...................................... 3

Revised SOT-23 Packages are Thinner ................................................................................. 3

Tiny Step-Down Switching Regulators Operate at

Megahertz Speeds—LTC1779/LT1616/LTC1701

Part 2: New Current Mode Regulators in SOT-23

New miniature high frequency switch-

ing regulators greatly expand the options

available to designers of portable and com-

munications products. Three of these new

products are supplied in the tiny SOT-23

package. (See Part 1 in the January issue for

similar devices in MSOP packages.) These

current mode devices deliver fast transient

response and excellent loop stability. Each

operate at high frequency for very low ripple

in sensitive bands and for tiny, low cost, sur-

face mount inductors and capacitors. They

each function at high duty cycles (Table 1)

for low dropout operation that extends

battery run time in portable systems. Two of

the devices use Burst Mode

operation for

ultralow power consumption when the con-

verter has very low load.

LTC is now converting its SOT-23

packages from a maximum height of

1.45mm to 1.0mm.

LTC1779 250mA, 94% Efficiency,

Output as Low as 0.8V

The constant frequency, 500kHz

LTC

1779 includes a 250mA MOSFET

switch on-board. The input voltage range of

2.5V to 9.8V enables 1-cell and 2-cell

lithium-ion conversions to outputs as low as

Table 1. New High Frequency, Current Mode Step-Down

Switching Regulators in SOT-23

LTC1779 LT1616 LTC1701* LTC1701B

OUT

Maximum 250mA 450mA 500mA 500mA

Input Range 2.5V to 9.8V 3.6V to 25V 2.5V to 5.5V 2.5V to 5.5V

Switching Frequency 550kHz** 1.4MHz** 1MHz 1MHz

Efficiency

†

94% 85% 94% 94%

Burst Mode Operation

REF

(Min V

OUT

) 0.8V 1.25V 1.25V 1.25V

Supply Current I

135µA 1.9mA 135µA 185µA

SHUTDOWN

8µA<1µA1µA1µA

Max Duty Cycle 100% 80% 100% 100%

Package SOT-23 SOT-23 SOT-23 SOT-23

*Introduced October 1999 **Constant frequency devices

†

Peak, 3.3V to 2.5V conversion (5V to 3.3V for LT1616)

0.8V (Figure 1). The high frequency allows

the use of a small, low height inductor.

Applications include portable products,

power supplies for ARMs, RISC processors

and distributed battery systems.

An accurate undervoltage lockout shuts

down the LTC1779 when the input voltage

falls below 2V. For further protection, the

overvoltage comparator in the LTC1779 will

turn the internal MOSFET off when the

feedback voltage has risen 7.5% above the

reference voltage of 0.8V.

The LTC1779 consumes only 135µA of

quiescent current to maximize battery life. In

shutdown, the device draws only 8µA. For

applications where efficiency at light loads is

a prime consideration, the LTC1779 is con-

figured for Burst Mode operation.

High Speed, Rail-to-Rail

Op Amps Provide High

Performance On 3V Sup-

plies—LT1806/LT1807

and LT1809/LT1810

The LT

1806/LT1807 are single and

dual rail-to-rail op amps optimized for use in

low noise, high performance communica-

tions systems. In addition to a low voltage

noise of 3.5nV/ , these amplifiers feature

a 325MHz gain-bandwidth product, a

140V/µs slew rate and an 85mA output cur-

rent. The 325MHz gain bandwidth and low

THD of –80dBc at 5MHz assures high per-

formance at low supply voltages. The unique

combination of low voltage operation, wide

bandwidth, low THD and low noise makes

the LT1806/LT1807 the perfect op amps in a

wide variety of applications, such as broad-

band digital communications, high speed

data acquisition and high performance video

applications (see Figure 1).

Continued on page 2

Continued on page 4

√Hz

Linear Technology Chronicle

• February 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.

LT1616: 600mA, 1.4MHz Fixed

Frequency, Inputs up to 25V

The LT1616 regulates a wide range of

power sources with voltages of 3.6V to 25V

such as 4-cell battery packs, 5V logic rails,

unregulated wall adapters and lead-acid

batteries. The 1.4MHz switching frequency

keeps switching noise well above the pass-

band of most communication systems. The

LT1616 remains in fixed frequency mode

even with light loads for systems needing the

lowest noise.

The complete LT1616 regulator foot-

print occupies less than 0.15in2 (1cm2). Its

600mA internal switch eliminates the need

for an external MOSFET and a sense resistor

(Figure 2). High efficiency, up to 85%,

reduces thermal dissipation compared to

other DC/DC converters. The shutdown

mode consumes very low current (less than

1µA) and completely disconnects the output

for easy power management. Built-in

current limiting protects against shorted

outputs.

LTC1701/LTC1701B: 500mA Regulators

Switch at 1MHz

The LTC1701 accepts inputs of 2.5V

to 5.5V (6V maximum) for long life in

single-cell Li-Ion or 3-/4-cell NiCd/NiMH

battery systems. The area used by the com-

plete regulator is less than 0.3in2 (2cm2).

The LTC1701 may also be configured as a

zeta converter for step-up/step-down

applications.

The output voltage is adjustable from

1.25V to 5V. The built-in 0.28Ω switch fur-

nishes up to 500mA of output current at 94%

efficiency. LTC’s unique OPTI-LOOP

ITH/RUN

LTC1779

20k 169k

78.7k

10Ω

22µH

100pF GND

VFB

1779 F01a

VIN

SENSE–

10µF

16V

0.1µF

C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT

C2: SANYO POSCAP 6TPA47M

D1: IR10BQ015

L1: COILTRONICS UP1B220

VIN

2.5V

TO 9.8V

VOUT

2.5V

100mA

47µF

BOOST

GND FB

SHDN SW

4.5V TO 25V

OFF ON 4

0.01µF

10µH

10k

16.5k

LT1616

10µF

1616 TA01

1µF

OUT

3.3V

300mA: V

= 4.5V TO 25V

400mA: V

= 4.7V TO 20V

C1: TAIYO-YUDEN TMK316BJ105

C2: TAIYO-YUDEN JMK316BJ106ML

D1: ON SEMICONDUCTOR MBR0530

D2: 1N4148

L1: SUMIDA CR43-100

Figure 1. LTC1779 High Efficiency 2.5V/100mA Step-Down Converter Figure 2. LT1616 Step-Down Converter, 3.3V Output

LTC1779/LT1616/LTC1701 from page 1

compensation enables fast transient

response. Automatic Burst Mode operation

maintains high efficiency at low output cur-

rents by reducing the switching losses. With

no load, the converter draws only 135µA; in

shutdown, it requires less than 1µA.

The low cost and low ESR of ceramic

capacitors make them attractive for use in

switching regulators. However, ceramic

capacitors are prone to changes with tem-

perature and their ESR is so low that they

cause loop-stability problems. OPTI-LOOP

compensation in the LTC1701 facilitates its

use in an all ceramic capacitor design.

The new LTC1701B version switches

continuously at 1MHz even with very low

loads for the lowest ripple and noise. The

quiescent current for this version is

185µA.

Fast Settling, True 16-Bit Voltage Output DAC

Includes Precision 4-Quadrant Resistors On-Chip—LTC1821

LTC1821-1

OUT

OFS

10 9

24 23 7

15pF

17 16

–

R1 R

COM

REF

11 12 14

0.1µF

122

OUT

15pF

OUT

1821 TA01

DGNDNC AGNDSAGNDF

–

LT1468

3 TO 6,

25 TO 36

CLR

16-BIT DAC

R1 R2

DATA

INPUTS

0.1µF

15V

–15V

0.1µF

–

DNC*

*DO NOT CONNECT

DNC*

REF

–V

REF

–V

REF

The LTC1821 is the industry’s first

voltage output DAC to offer true 16-bit lin-

earity over the industrial temperature range

as well as 2µs settling time for precision ap-

plications. This combination of precision

performance and 16-bit accuracy makes it

suitable for digital waveform generation as

well as data acquisition, automatic test

equipment, process control and industrial

automation. The LTC1821 comes in two

16-bit monotonic grades. The A grade offers

±1LSB INL whereas the B grade offers

±2LSB INL, both over industrial and com-

mercial temperature ranges.

4-quadrant multiplication is achieved

with on-chip 4-quadrant multiplication resis-

tors. These on-chip resistors simplify the

connection to an external op amp for multi-

plying the reference input and configuring

the analog output for unipolar or bipolar

Figure 1. LTC1821 Block Diagram

Continued on page 3

Linear Technology Chronicle

• February 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

FET Input, Fast, High Gain Photodiode Amplifier Using the LT1806

The LT1806 is a low noise rail-to-rail

input and output unity-gain stable op amp

that features a 325MHz gain bandwidth

product, a 140V/µs slew rate and an 85mA

output current. It is optimized for low volt-

age, high performance signal conditioning

systems.

Figure 1 shows a fast, high gain

transimpedance amplifier applied to a pho-

todiode. A JFET buffer is used for its

extremely low input bias current and high

speed. The LT1097 and 2N3904 keep the

JFET biased at I

DSS

for zero offset and

lowest voltage noise. The JFET then drives

the LT1806, with R

closing the high speed

loop back to the JFET input and setting the

transimpedance gain. C4 helps improve the

phase margin of the fast loop. Output volt-

age noise density was measured as 9nV/

with R

short circuited. With R

varied

from 100k to 1M, total output noise was

below 1mV

RMS

measured over a 10MHz

bandwidth. Table 1 shows results achieved

with various values of R

and Figure 2

shows the time domain response with

= 499k.

Table 1. Results Achieved for Various

RF, 1.2V Output Step

10% TO 90%

RISE TIME –3dB BANDWIDTH

100k 64ns 6.8MHz

200k 94ns 4.6MHz

499k 154ns 3MHz

1M 263ns 1.8MHz

–

10k

10M

SIEMENS/

INFINEON

SFH213FA

PHOTODIODE R2

49.9Ω

50Ω

18067 F10

33Ω

2.4k

VS+

VS–

2200pF

0.1µF

100pF

3pF

LT1097

–

VOUT

2N5486

VS+

VS–

3LT1806

2N3904 *ADJUST PARASITIC CAPACITANCE AT

RF FOR DESIRED RESPONSE

CHARACTERISTICS

VS = ±5V

Figure 1. Fast, High Gain Photodiode Amplifier

100mV/DIV

18067 F11

Figure 2. Step Response

with RF = 499k

√Hz

LTC1821 from page 2

ranges. The resistor connections allow 0V to

10V, 0V to –10V or ±10V output ranges

with ±15V supplies.

An asynchronous clear pin resets the

LTC1821 to zero scale while the LTC1821-1

is reset to midscale allowing bipolar applica-

tions to reset to zero volts. The LTC1821

and LTC1821-1, both A and B versions, are

available in the commercial and industrial

temperature ranges. All versions of the

LTC1821 devices are packaged in the 36-pin

SSOP package, providing a much smaller

design than comparable parallel input

DACs.

DIGITAL INPUT CODE

INTEGRAL NONLINEARITY (LSB)

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

–0.6

–0.8

–1.0 16384 32768

1821 TA02

49152 65535

VREF = 10V

VOUT = ±10V BIPOLAR

LTC1821/LTC1821-1 Integral

Nonlinearity

Revised SOT-23

Packages are Thinner

LTC is putting into production as of

January 2001, revised 5-lead and 6-lead

SOT-23 packages that are thinner in height.

This change is in response to customer

desires to make even thinner circuits. The

previous maximum thickness (height from

the board) was 1.45mm. The revised maxi-

mum height is 1.0mm.

The revised packages will be used on

new builds of all products that are supplied

in these packages. Shipments of products in

the revised packages will begin Spring 2001.

Contact your sales office or distributor for

details.

Linear Technology Chronicle

• February 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.

In addition to the low voltage low noise

performance, the overall DC precision of

these high speed op amps is unmatched by

any competitive device. A maximum offset

voltage of less than 0.5mV, CMRR of

106dB and a large-signal voltage gain of

300V/mV dispel any concerns about low

voltage operation.

The LT1806/LT1807 have an input

range that includes both supply rails and an

output that swings within 20mV of either

supply rail to maximize the signal dynamic

range in low supply applications. The

LT1806/LT1807 maintain their performance

for supplies from 2.5V to 12.6V and are

specified at 3V, 5V and ±5V supplies. With

the LT1806/LT1807, you can now lower

your systems supplies without losing preci-

sion and bandwidth.

The LT1806 is available in an 8-pin SO

package with the standard op amp pinout

and a 6-pin SOT-23 package. The LT1807

features the standard dual op amp pinout and

is available in 8-pin SO and MSOP pack-

ages. Both parts are available in commercial

and industrial temperature grades.

LT1806/LT1807 and LT1809/LT1810 from page 1

The LT1809/LT1810 are single and

dual rail-to-rail input and output op amps

optimized for use in low voltage, high per-

formance signal conditioning systems. With

180MHz gain bandwidth, 350V/µs slew rate

and low THD of –90dBc up to 5MHz (see

Figure 2), the LT1809/LT1810 are the first

op amps designed for 3V broadband applica-

tions. A wide input common mode range that

includes both rails and a rail-to-rail output

stage that is guaranteed to swing within

20mV of either rail offers exceptional

dynamic range. The LT1809/LT1810 main-

tain their performance for supplies from

2.5V to 12.6V and are specified at 3V, 5V

and ±5V supplies. The inputs can be driven

beyond the supplies without damage or

phase reversal of the output.

This unique combination of low distor-

tion, rail-to-rail input and output and low

supply voltage operation makes the LT1809/

LT1810 the first op amps to support com-

plete 3V system design of broadband com-

munication, high performance video and

high speed data acquisition systems.

The LT1809 is available in the 8-pin SO

package with the standard op amp pinout

and the 6-pin SOT-23 package. The LT1810

features the standard dual op amp pinout and

is available in 8-pin SO and MSOP pack-

ages. Both devices are available in both

commercial and industrial temperature

ranges.

Table 1. Operating Performance for

LT1806/LT1807 and LT1809/LT1810

LT1806/ LT1809/

LT1807 LT1810

Gain-Bandwidth 325MHz 320MHz

Product

Slew Rate 140V/µs 350V/µs

THD –80dBc –90dBc

Voltage Noise 3.5nV/

√Hz

16nV/

√Hz

Offset Voltage 700µV 3.5mV

Bias Current 5mA 10mA

CMRR 83dB 70dB

VOL

100dB 89dB

Supply Current 16mA 20mA

Per Amp

–

1/2 LT1807

909Ω

49.9Ω

100Ω

100ΩC1 5.6pF

C2 5.6pF

–

1/2 LT1807

470pF

LTC1420

PGA GAIN = 1

REF

= 4.096V

12 BITS

10Msps

+AV

–5V

18067 TA01

–AV

Figure 1. Gain of 20 Differential A/D Driver Using LT1807

FREQUENCY (MHz)

0.3

–70

DISTORTION (dB)

–60

–50

–40

11030

1809 TA02

–80

–90

–100

–110

= +1

= 2V

P-P

= ±5V

= 100Ω, 2ND

= 1k, 3RD

= 1k, 2ND

= 100Ω, 3RD

Figure 2. Distortion vs Frequency

for the LT1809

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