October 2000 - Linear Technology

Linear Technology Chronicle

• October 2000 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, No Latency Delta-Sigma,

No Latency ∆Σ and C-Load are trademarks of Linear Technology

Corporation.

Linear Technology Chronicle

October 2000 Vol. 9 No. 10

Inside This Issue:

24-Bit No Latency Delta-SigmaTM ADC with Differential Inputs

Fits in MSOP Package—LTC2411 ......................................................................................... 2

Amplifier with ±42V Common Mode Input Range on a Single 5V Supply

Without Sacrificing Differential Gain—LT1884........................................................................ 3

Dual and Quad Rail-to-Rail Output, Picoamp Input Precision Op Amps—LT1881/LT1882 ... 3

New LDO Regulators Have Lowest Noise, Withstand Reverse Voltage and Operate

with Low Cost Ceramic Capacitors—LT1962/LT1963 ............................................................ 4

Figure 1. 3.3V to 5V/450mA Step-Up

DC/DC Converter

First 1A Switching Regulators in SOT-23 Package

Have Low Noise and Switch at 1.2MHz—

LT1930 and LT1931

The LT

1930 and LT1931 are the only

SOT-23 switching regulators on the market

that include an integrated 1A switch. Their

high 1.2MHz switching frequency enables

the use of small, low cost capacitors and

inductors, minimizing the total PCB foot-

print and maintaining a height profile below

2mm. Their constant high frequency keeps

the output noise low and predictable so that

output voltage ripple of less than 5mVP-P is

easily achievable.

With an input voltage range of 2.6V to

16V, the LT1930 and LT1931 are a good fit

for a variety of input sources. The onboard

switch features a low VCESAT voltage of

400mV at 1A, resulting in very good effi-

ciencies even at high load currents. Their

36V switches allow outputs as high as 34V

or –34V. The devices are pin compatible

with other LTC devices for simple upgrades

and design flexibility.

An integrated shutdown function limits

the supply current to 0.01µA (typical) when

the part is disabled. Shutdown virtually

eliminates battery drain, extending operating

time in portable devices.

LT1930: 1A Switcher for Boost, SEPIC

and Flyback

The LT1930 is a 1A boost DC/DC converter

in a 5-lead SOT-23 package. It offers the

smallest solution size (8mm × 10mm) for

generating a 5V (at 400mA) output from a

battery voltage as low as 2.6V. The 36V

rated switch is useful for boost converters up

to 34V, as well as for buck-boost SEPIC

(single-ended primary inductance convert-

ers) and flyback designs. The LT1930 can

generate 480mA at 5V from a 3.3V input

(Figure 1) or 300mA at 12V from a 5V

input.

Small form factor, minimal external

parts count and high efficiency make the

LT1930 a good choice for conversion needs

in modems, xDSL power supplies, PDAs

and medical diagnostic equipment. The

device is pin-to-pin compatible with the

lower power fixed frequency LT1613 and

the LT1615 with Burst Mode

operation.

GND

SHDN FB

5.6µH

40.2M

LT1930

1930 TA04

10µF

4.7µF

13.3k

OUT

480mA

C1: TAIYO-YUDEN X5R JMK212BJ475MG

C2: TAIYO-YUDEN X5R JMK316BJ106ML

D1: ON SEMICONDUCTOR MBR0520

L1: SUMIDA CR43-SR6

SHDN

LT1931: Low Noise Inverting 1A Switch-

ing Regulator

The LT1931 SOT-23 inverting switch-

ing regulator has an on-chip 1A switch that

allows high output currents. In a typical 5V

to –5V application the part can deliver

350mA. Its low noise architecture makes it

perfect for supplying critical negative bias

for disk drive MR heads, GaAs FETs, digital

camera CCDs and LCDs. The device is pin-

for-pin compatible with the lower power

constant frequency LT1611 and the LT1617

with Burst Mode operation.

Low Noise, High Speed

Rail-to-Rail Op Amp

Operates on Supplies as

Low as 2.5V Without

Compromising

Performance—LT1806

The LT1806 offers a unique combina-

tion of low voltage operation, wide band-

width, low distortion and low noise. The

325MHz unity-gain bandwidth product, low

THD of –80dBc at 5MHz and 3.5nV/

noise ensures high performance at low volt-

ages, perfect for a wide variety of applica-

tions such as high speed data acquisition,

broadband digital communications and high

performance video systems.

In addition to the low voltage noise per-

formance, the overall DC precision of this

high speed op amp is unmatched by any

competitive device. A maximum offset volt-

age of less than 0.5mV, CMRR of 106dB

and a large-signal voltage gain of 300V/mV

dispel any concern about DC accuracy at

low voltages. The LT1806 also features a

shutdown pin that reduces power consump-

tion to less than 2mW on a 3V supply.

√Hz

Continued on page 2

Continued on page 4

Linear Technology Chronicle

• October 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.

LT1806 from page 1

As systems migrate to lower supply

voltages, dynamic range becomes precious.

The LT1806 maintains its performance for

supplies from 2.5V to 12V and is fully speci-

fied on 3V, 5V and ±5V supplies. The

LT1806 has an input range that includes

both supply rails and an output that swings

within 20mV of either supply rail. This

combination of low minimum supply voltage

and rail-to-rail input and output maximizes

the signal dynamic range in low supply volt-

age applications. The part’s high 85mA out-

put current and low distortion also makes it

useful as a line driver, cable driver or buffer

amplifier.

–

LT1806

1806 TA01

33µF

150µF

75ΩR

LOAD

75Ω

OUT

75Ω

COAX CABLE

1000µF

The LT1806 is available in the 8-pin SO

package for operation over the industrial and

commercial temperature ranges. Available in

the standard 8-pin pinout, the LT1806 can

easily be used to upgrade existing sockets

moving to lower supply voltages or requiring

higher performance.

Figure 1. LT1806 3V Single Supply Video Line Driver

24-Bit No Latency Delta-

Sigma ADC with

Differential Inputs Fits in

MSOP Package—

LTC2411

Packaged in the tiny 10-pin MSOP, the

LTC

2411 is the smallest 24-bit analog-to-

digital converter (ADC) with differential

inputs and reference available today. The

10-lead MSOP package is less than half the

size of an SO-8 and allows the LTC2411 to

fit within the shell of a sensor or transducer.

Operating from a supply as low as 2.7V, the

part consumes just 200µA during conversion

and 3µA during auto shutdown, extending

battery life in portable instruments. The dif-

ferential reference voltage can range from

0.1V to VCC, providing the flexibility to

operate in ratiometric and remote sensing

applications. The LTC2411 is not only small

and low power, but also very accurate and

offers a host of integrated features that make

it very easy to use.

The LTC2411 performs transparent off-

set and full-scale calibration on every con-

version to provide 5ppm total unadjusted

error, 0.5ppm offset error, 4ppm full-scale

error and 4ppm integral nonlinearity (INL).

It has a proprietary No Latency ∆Σ

archi-

tecture that allows its digital filter to settle in

a single cycle, eliminating the need to throw

away data after an input signal step, as

required with other high resolution ADCs.

Transparent calibration and single-cycle set-

tling dramatically simplify system software

development.

Another integrated feature is the highly

accurate on-chip oscillator that eliminates

the need for external frequency setting com-

ponents such as crystals or external clock

sources. The 4th order sinc filter rejects line

frequencies to 110dB and is pin selectable

between 50Hz or 60Hz or can be tuned with

an external clock input. The external clock

feature allows the LTC2411 to output data

as fast as 15Hz without compromising the

accuracy or to output data faster with

reduced resolution.

The LTC2411 is available in the MS-10

package in both commercial and industrial

temperature ranges.

LTC2411

IN+

REF+VCC

REF–

VCC

GND FO

IN–

1µF

SDO

3-WIRE

SPI INTERFACE

SCK

2411 TA02

610

BRIDGE

IMPEDANCE

100Ω TO 10kΩ

Figure 1. LTC2411 Directly Digitizes Bridge Output

Linear Technology Chronicle

• October 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

Amplifier with

42V Common Mode Input Range On a Single 5V Supply

Without Sacrificing Differential Gain—LT1884

Measuring small voltages on top of

large voltages can be quite difficult. Often,

the standard difference amplifier topology

is implemented with very high value input

resistors and low value divide and feedback

resistors, as shown in Figure 1. However,

this results in significant differential mode

attenuation.

The circuit in Figure 2 uses an LT1884

to achieve high common mode input range

and rejection without sacrificing differential

gain. U1B samples the common mode

through R5 and R6 and nulls it through R3

and R4. The R3-R1 ratio must be extremely

well matched to the R4-R2 ratio to avoid

Figure 2. Single Supply Difference Amplifier. U1B Nulls the Common Mode

So That U1A Can Concentrate on the Difference Mode

Figure 1. Standard Difference Amplifier

Can Handle High Voltage Common Mode

Inputs, But at Cost of Differential Gain

causing a common mode to differential

mode translation at this point. Once the com-

mon mode is nulled, the differential mode

input voltage is converted to a differential

input current and appears unattenuated

across R7. The common mode input voltage

can theoretically be as high as about 250V

(limited by the output of U1B going to

ground and the ÷100 ratio maintaining com-

mon mode at 2.5V), but is limited in fact by

the working voltage of R1 and R2 and by the

ratio matching of R1-R3 and R2-R4.

The LT1884 dual op amp combines

rail-to-rail outputs, 2MHz gain bandwidth

product and excellent DC precision. Its low

drift input offset voltage is trimmed to

80µV while its input offset and input bias

currents are a maximum of 900nA. The

LT1884 and the quad LT1885 operate over

an input range of 2.7V to 36V (or to ±18V).

Supply current is 1mA maximum per

amplifier.

DN230 F02

10k

10k REF

–

U1A

1/2 LT1884

U1B

1/2 LT1884

10k

R6*

10k

*1% METAL FILM

†

CADDOCK (541) 496-0700 T912 0.01% MATCHED RESISTOR PAIRS

†

10k

= 42V

P-P

= ±2.5V

†

10k

R5*

10k

LT1634B-2.5

DN230 F03

R7*

R8*

OUT

2.5V ±V

†

–

†

Dual and Quad Rail-to-Rail Output, Picoamp Input

Precision Op Amps—LT1881/LT1882

The LT1881 and LT1882 offer unsur-

passed DC precision in a rail-to-rail op amp.

The high input precision includes bias and

offset currents of 500pA, input offset voltage

of less than 80µV and a maximum offset

drift of 0.8µV/°C. The LT1881 is also of-

fered in an A grade with reduced bias and

offset current of 200pA max and an input

offset voltage of 50µV. A high 114dB

CMRR and an open-loop gain of 120dB add

to the precision performance of the parts.

AC specs include a gain bandwidth of

1.1MHz (typ) and 0.4V/µs slew rate.

The amplifiers work on any total power

supply voltage between 2.7V and 36V (fully

specified at 5V and ±15V). The rail-to-rail

output voltage swings to within 40mV of the

negative supply and 220mV of the positive

supply, making these amplifiers an excellent

choice for low voltage single supply opera-

tion. Both parts are also C-Load

stable,

driving capacitive loads of up to 1000pF in

unity gain.

The dual LT1881 and LT1881A are

available with standard pinouts in SO-8 and

PDIP packages. The quad LT1882 is in a

14-pin SO package. The LT1881 and

LT1882 are available in both commercial

and industrial temperature grades. For a

higher speed device with similar DC specifi-

cations, Linear Technology offers the

LT1884/LT1885.

Table 1. Dual and Quad Rail-to-Rail Output, Picoamp Input Precision Op Amps

Offset Offset Bias Offset Gain Slew

Voltage Drift Current Current Bandwidth Rate

(Max) (Max) (Max) (Max) (Typ) (Typ)

LT1881/LT1882 80µV0.8µV/°C 500pA 500pA 1.2MHz 0.4V/µs

LT1881A 50µV0.8µV/°C 200pA 200pA 1.2MHz 0.4V/µs

LT1884/LT1885 80µV0.8µV/°C 900pA 900pA 2MHz 0.9V/µs

LT1884A 50µV0.8µV/°C 400pA 300pA 2MHz 0.9V/µs

Linear Technology Chronicle

• October 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.

New LDO Regulators Have Lowest Noise, Withstand Reverse Voltage and

Operate with Low Cost Ceramic Capacitors—LT1962/LT1963

The LT1962 and LT1963 are the latest

members of LTC’s advanced low dropout

voltage (LDO) regulator family (Table 1).

The devices operate from 2.3V to 20V input

supplies, offering compatibility with a wide

variety of input power sources. Built-in pro-

tection circuitry in these regulators guards

against reverse current flow without requir-

ing external protection diodes. In addition,

the outputs can be pulled below ground

without damaging the devices. Other protec-

tion includes current limiting and thermal

limiting.

LT1962: 300mA, 300mV Dropout and

Low Supply Current

The LT1962 is a micropower regulator

that offers the lowest supply current and the

lowest noise in the industry. Sourcing up to

300mA with only 270mV* dropout in a tiny

8-lead MSOP package, the device is ideal for

powering embedded processors and DSPs in

applications such as notebook PCs, PDAs,

cellular phones and portable instruments.

By using a tiny 0.01µF bypass capaci-

tor, only 20µVRMS output noise over a

10kHz to 100kHz bandwidth is generated by

the LT1962. Supply current is only 30µA

operating and less than 0.5µA in shutdown

mode, virtually eliminating battery drain.

The design works with all types of capaci-

tors in values as low as 3.3µF and is stable

using low ESR, low cost ceramic capacitors,

allowing the smallest total solution for

space-constrained applications.

Output voltages are fixed at 1.5V, 1.8V,

2.5V, 3.3V and 5V or can be adjusted

between 1.22V and 20V.

LT1963: 1.5A with Fast Transient

Response

The LT1963 is a fast transient response,

low noise regulator for multipurpose use

over wide input and output voltage ranges. It

can deliver up to 1.5A with only a 340mV

dropout and with only 40µVRMS output

noise over a 10Hz to 100kHz bandwidth,

which makes it useful for powering noise-

sensitive RF circuits. Very low dropout

means it will regulate 2.5V supplies from a

3.3V input. The LT1963 is ideal for power-

ing FPGAs, ASICs and DSPs in applications

such as telecommunications, data processing

and networking.

Stable with all types of capacitors,

including low ESR, surface mount ceramic

capacitors, the LT1963 provides the small-

est total solution. Its supply current of 1mA

is reduced to less than 1µA in shutdown.

Outputs of 1.5V, 1.8V, 2.5V, 3.3V

and a version that can be adjusted between

1.21V and 20V are each available in an

8-lead SO, SOT-223, 5-lead TO-220 and

DD packages.

*Typical values unless stated otherwise. See data

sheets.

Table 1. Low Noise, Low Dropout Regulator Family

RMS Noise Dropout

Output Quiescent 10Hz to 100kHz Voltage at

Device Current Current C

BYP

= 0.01µF Packages Max Output

Micropower

LT1761 100mA 20µA20µV SOT-23 0.34V

LT1762 150mA 25µA20µV MSOP-8 0.27V

LT1962 300mA 30µA20µV MSOP-8 0.27V

LT1763 500mA 30µA20µV SO-8 0.3V

Fast Transient

LT1963 1.5A 1mA 40µV SO-8, SOT-223 0.34V

DD, TO-220

LT1764 3A 1mA 40µV DD, TO-220 0.34V

LT1930 and LT1931 from page 1

The LT1931 may use tiny uncoupled

inductors to fit within a 0.1 in2 (65mm2)

area. This circuit has an output voltage ripple

of only 6mVP-P. In applications where soft-

start is required, a resistor, a diode and a ca-

pacitor may be added to the shutdown circuit

to limit how quickly VOUT can be

charged.

OUT

–5V

350mA

1931 F01

10µHL2

10µH

GND

LT1931

OPTIONAL

SOFT-START

C1: TAIYO YUDEN X5R JMK212BJ475MG

C2: TAIYO YUDEN X5R LMK212BJ105MG

C3: TAIYO YUDEN X5R JMK325BJ226MM

D1: ON SEMICONDUCTOR MBR0520

L1, L2: LQH3C100K04

4.7µFC3

22µF

1µF

10k

29.4k C4

220pF

NFB

SHDN

Figure 2. 300mA 5V TO –5V Converter Fits in 0.1in2 (65mm2)

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