August 1998 - Linear Technology

Linear Technology Chronicle •

August 1998

A Showcase of Linear T echnology’ s Focus Products

Linear Technology Chronicle

August 1998 Vol. 7 No. 8

Product of the Month

LTC1412: 12-Bit, 3Msps ADC—Speed,

Performance, Low Power, No Pipeline Delay

A new 12-bit 3Msps ADC brings

unparalleled levels of performance and ease

of use to circuit designers. Excellent

dynamic specifications enable high speed

modem designs with cleaner signals over

greater distances. Low noise and high DC

performance fit it for CCD imaging. No

pipeline delay facilitates servo-loop and mo-

tor control, DSP, sampling systems and

multiplexed data acquisition. Low power and

small package size make it easy for everyone

to live with.

SAR Architecture, Clean and Simple

The LTC

1412’s successive approxi-

mation (SAR) design avoids the many

problems found in pipelined and subranging

ADCs in the Msps speed range. These prob-

lems include compromised AC and DC

performance, general operational misbehav-

ior and cumbersome analog support

circuitry. Other pipeline drawbacks are poor

noise and SNR, pipeline delay (latency), no

three-state outputs, poor frequency domain

performance and large package and power

dissipation.

Conversion data is present at the

LTC1412’s three-state outputs 300ns after

the conversion begins. Inputs can be multi-

plexed. The new LTC1412 is the only clean,

simple-to-use alternative faster than

1.25Msps.

Cleaner Behavior and Superior Linearity

The LTC1412 depends solely on capaci-

tor matching for accuracy. This results in

typical 0.25LSB INL and DNL (Figures 1

and 2) that have nearly zero drift with time,

temperature, supply voltage or reference

voltage. There is virtually no potential for

sparkle codes to which pipelined ADCs are

susceptible.

Lower Noise

Pipelined ADCs add noise to their con-

version because they resample the input

signal as the conversion moves through the

converter. The LTC1412 has nearly perfect

noise performance because its single

sample-and-hold and single-pass conversion

add almost no noise. Its 73dB (typical) SNR

at 3Msps is within 1dB of the theoretical

quantization noise. The LTC1412 also has

premier distortion performance of 80dB at

its Nyquist frequency.

Simple Input and Reference Circuitry

The LTC1412’s high impedance, dif-

ferential input sample-and-hold eliminates

the level shifting, complementary differen-

tial input or transformers typically used in

single supply ADCs. The internal reference

does away with the multiple reference pins,

multiple bypassing caps and fast reference

buffer amps commonly used with pipeline

converters. The LTC1412 reference allows

slow and fast span adjustments and main-

tains linearity over a 2:1 reference voltage

range.

The unique sample-and-hold circuit

provides a wide, 40MHz full-power input

bandwidth that allows the circuit to under-

sample signals far above the converter’s

Nyquist frequency and preserve their

fidelity. The common mode rejection of

60dB is especially useful for suppressing the

perturbating effects of common mode noise

and ground loops.

Size and Power Efficiency

The LTC1412’s simple, efficient archi-

tecture and low power dissipation (150mW)

allow small 28-lead SSOP packaging. Thus,

the LTC1412 offers the smallest footprint

among 3Msps, parallel-output ADCs plus

generally fewer external components (see

Figure 3).

Inside This Issue:

LT1167: Industrial-Strength Instrumentation Amplifier, Single Resistor Sets Gain .................. 2

LTC1515: Battery-Powered Buck-Boost Converter Requires No Magnetics ........................... 3

LTC1710: SMBus Compatible High Side Switches ................................................................. 3

LT1780/LT1781: 15kV ESD Protected RS232 Transceivers .................................................. 4

LTC1542: Micropower Op Amp and Comparator ................................................................... 4

OUTPUT CODE

–1.0

DNL (LSBs)

–0.5

0.5

1.0

512 1024 1536 2048

1412 G06

2560 3072 3584 4096

, LTC and LT are registered trademarks of Linear Technology

Corporation.

OUTPUT CODE

–1.0

INL (LSBs)

–0.5

0.5

1.0

512 1024 1536 2048

1412 G07

2560 3072 3584 4096

Figure 2. Integral Nonlinearity

vs Output Code

Figure 1. Differential Nonlinearity

vs Output Code

Figure 3. Complete 3Msps 12-Bit

ADC System (175% of Actual Size)

Continued on page 2

Linear Technology Chronicle •

August 1998

determined by the tolerance of the external

resistor.

The low gain error is maintained over

the output voltage range. Since gain

nonlinearity (GNL) cannot be trimmed, the

LT1167 was designed to cancel gain errors

due to die stress and thermal gradients. Gain

error and GNL over temperature are fully

specified for the LT1167.

Gain nonlinearity can contribute signifi-

cant system error, especially at higher gains

and larger loads. Figure 1 shows the GNL of

a competitive device into a 1kΩ load at a

gain of 1000. The LT1167 exhibits the

greatly improved GNL as shown in Figure 2.

Ideal for Many Applications

The ability to operate at ±3V on 0.9mA

makes the LT1167 ideal for battery-powered

systems. Its low current noise and low volt-

age noise make it ideal for ECG monitors

that have megohm source impedances. The

LT1167’s ruggedness, accuracy, wide supply

voltage range, ease of use and small size

make it suitable for a broad range of preci-

sion data acquisition, medical instrument-

ation, industrial measurement and process

control and flow control applications. Con-

tact 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 LT1167: Industrial-Strength Instrumentation

Amplifier, Single Resistor Sets Gain

The LT

1167 is the next generation

instrumentation amplifier. Gain from 1 to

10,000 is set with a single external resistor.

It has improved performance and features

over other monolithic instrumentation amps

and has improvements over multiple op amp

solutions. The LT1167 combines excellent

DC precision with industrial-quality fault

protection. The pinout and gain equation are

compatible with other monolithic instrumen-

tation amps, allowing easy upgrade for

existing products.

4kV ESD Input Protection

Instrumentation amplifiers are subjected

to hostile environments, connected to sen-

sors and input lines that experience voltage

and current transients and ESD. The LT1167

is designed with low leakage internal protec-

tion diodes from each input to the supplies.

These diodes have a current rating of 20mA

and protect the IC when the input voltage

exceeds the supply rails.

Because of the ultralow 350pA bias cur-

rent of the LT1167, high value resistors in

series with the inputs do not degrade VOS.

For example, 10% tolerance 100k resistors

add only 5µV of offset to the LT1167. With

20k resistors, the LT1167 can handle both

±400VDC input faults and ESD spikes over

4kV. This meets the IEC 1004-2 level 2

European standard. Higher value resistors

can be used for higher voltage protection.

Industry Best DC Performance

The LT1167 input bias current is com-

parable to that of a JFET input stage at room

temperature. However, IB for the LT1167

does not double for every 10°C rise as do

JFET types. At 85°C, it is still less than 1nA.

The LT1167 is trimmed to meet critical

DC parameters over a wide range of operat-

ing conditions. Input-referred offset voltage

is only 15µV at 25°C and 40µV over the

industrial temperature range (typical values).

Common Mode Rejection Ratio (CMRR) is

a minimum of 90dB and 106dB at gains of 1

and 10. Power Supply Rejection Ratio

(PSRR) is guaranteed at 109dB and 125dB.

CMRR and PSRR are tested and guaranteed

over temperature. Competing devices are not

specified over temperature.

Single Gain-Set Resistor, Low Gain

Nonlinearity

Gain is easily set with a single external

resistor. No expensive matched resistor

arrays are needed. Gain error is trimmed to a

very low 0.04% worst-case over temperature

(at a gain of 1). The system gain accuracy is

Figure 1. Gain Nonlinearity of a Previous

Generation Instrumentation Amp:

RL = 1k; VO =

10V

GAIN

NONLINEARITY

100PPM/DIV

GAIN

NONLINEARITY

100PPM/DIV

Figure 2. LT1167 Gain Nonlinearity:

RL = 1k; VO =

10V

High Speed, High Resolution Applications

The LTC1412 is designed for applica-

tions such as telecom digital-data transmis-

sion, wide bandwidth multichannel data

acquisition and baseband signal recovery

through undersampling. Its simple parallel

LTC1412 from page 1

interface and conversion start signal make it

easy to use in DSP-based designs.

Now there is a clean 12-bit, 3Msps

ADC alternative: the LTC1412. It does

everything a pipelined ADC does, and bet-

ter, but without the drawbacks. For a data

sheet and evaluation samples, contact your

local Linear Technology sales office. For

more information, visit our web site at

www.linear-tech.com.

Linear Technology Chronicle •

August 1998

Application of the Month

Battery-Powered Buck-Boost Converter Requires No Magnetics

One of the problems that designers of

portable equipment face is generating a

regulated voltage that is between the

charged and discharged voltage of a battery

pack. As an example, when generating a

3.3V output from a 3-cell battery pack, the

regulator input voltage changes from about

4.5V at full charge to about 2.7V when dis-

charged. At full charge, the regulator must

step down the input voltage, and when the

battery voltage drops below 3.3V, the regu-

lator must step up the voltage. The same

problem occurs when a 5V output is

required from a 4-cell input voltage that

varies from about 3.6V to 6V. Ordinarily, a

flyback or SEPIC configuration is required

to solve this problem.

The LTC1515 switched-capacitor

DC/DC converter can provide this buck-

boost function for load currents up to 50mA

with only three external capacitors. The

circuit shown in Figure 1 will provide a

regulated 3.3V output from a 3-cell input or

a 5V output from a 4-cell input. Connecting

the 5/3 pin to VIN will program the output to

5V, whereas grounding the 5/3 pin programs

the output to 3.3V.

The absence of bulky magnetics pro-

vides another benefit; this circuit requires

only 0.07 square inches of board space in

those applications where components can be

mounted on both sides of the board. The

addition of R1 provides a power-on reset

flag that goes high 200ms after the output

reaches 93.5% of its programmed value. The

SHDN pin allows the output to be turned on

or off with a 3V logic signal.

Figure 1. Battery-Powered

Buck-Boost Converter

LTC1710: SMBus Compatible High Side Switches

Two 0.4

Ω

Switches in MSOP-8

The LTC1710 High Side SMBus dual

switch is a complete solution for supplying

power to portable equipment peripherals.

Two high side 0.4Ω N-channel MOSFET

switches, with 300mA capability and inde-

pendent drains, are included in the tiny

MSOP-8 package. The circuit is fully com-

patible with SMBus and I2C

prototcols.

With ultralow standby current (14µA), the

LTC1710 is a perfect fit for handheld elec-

tronics and other space-constrained

applications.

Internal Charge Pumps and Capacitors

To fully enhance the power switches,

the LTC1710 uses a charge pump tripler to

boost and regulate the gate drive of each

switch (Figure 1). Running at about 300kHz,

each charge pump is programmed to supply a

ramped voltage to the gate of each switch, so

that it turns on smoothly, avoiding large cur-

rent spikes into the load. The charge pump

capacitors are integrated on the IC.

Independent Voltage Control;

Fault Protection

The drains of the two switches are inde-

pendent of each other. As a result, SMBus

peripherals requiring different input voltages

can be simultaneously switched by the

C is a trademark of Philips Electronics N.V.

Three-State Programmable

Address Input

The SMBus is a serial bus interface that

uses only two bus lines, DATA and CLK, to

control low power peripheral devices in por-

table equipment. The LTC1710 operates over

an input voltage range of 2.7V to 5.5V and

maintains the SMBus specified 0.6V VIL and

1.4V VIH thresholds throughout.

To identify itself on the SMBus, the

LTC1710 has a three-state programmable

address pin that can be tied to VCC, to ground

or to VCC/2 with the help of two 1M resis-

tors. Thus, a total of six switches may be

controlled on the same bus. The format of the

address places the LTC1710 directly in the

reserved address range for power-plane

switching.

The LTC1710 features a double-buffered

output. The Stop signal can be used to syn-

chronize the output executions of several

differently-addressed peripherals whose data

were loaded at different times.

Compact, Complete Power Management

With two built-in 0.4Ω power switches

in an MSOP-8 or SO-8 package and low

standby current, the LTC1710 is an ideal

solution for delivering up to 300mA to

SMBus peripherals in complex portable

equipment. For a data sheet and evaluation

samples, contact your local Linear Technol-

ogy sales office. For more information, visit

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

LTC1710 (see Figure 1). If too much output

current is sourced, an internal thermal shut-

down circuit protects the system by turning

off both switches.

A power-on reset signal ensures that

the LTC1710 starts up with both switches

off. The POR signal inhibits operation until

about 300µs after VCC crosses the under-

voltage lockout threshold. The system

includes some hysteresis and delay to avoid

nuisance resets.

2.7V FAN

5V

DISPLAY

LTC1710

AD1

DATA

CLK

SW1

SW0

1710 F01



2.7V TO 5V SW0D

GND TO V

10µF10µF

FROM SMBus

CHARGE

PUMPS

Figure 1. The LTC1710 Switches Two

SMBus Peripherals with Different

Input Voltages

SHDN

POR

GND

5/3

OUT

–

LTC1515-3.3/5

C1

0.1µF

(0603)

C1 = AVX 0603YC104MAT2A

C2, C3 = MURATA GRM235Y5V106Z

C2

10µF

16V

(1210)

R1

100k

3.3V/50mA

OR

5V/50mA

ON OFF

3 OR 4

CELLS

RESET

5V 3.3V

1515 F01

Linear Technology Chronicle •

August 1998

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:

Arrow Electronics

Digi-Key

Electrosonic

Gerber Electronics

Marshall Industries

Phase 1

15kV ESD Protected

RS232 Transceivers—

LT1780/LT1781

The LT1780 and LT1781 are dual

RS232 transceivers that provide ESD protec-

tion compliant with the International

Electrotechnical Commission’s 1000-4-2

(Level 4) specification. The circuits operate

from a single 5V supply and the LT1780

offers a low power shutdown mode.

Each device includes two drivers and

two receivers. This configuration provides

the basic RS232 signals used in industrial,

instrumentation and medical applications.

ESD Protection

These transceivers are designed for

equipment with serial ports that may not be

protected from the environment. Therefore

the driver outputs and receiver inputs include

ESD protection structures. The LT1780 and

LT1781 meet the stringent European

standards:

IEC 1000-4-2:15kV Air Gap

Discharge Method

IEC 1000-4-2:8kV Contact Discharge

Method

Compliance with the IEC ESD require-

ments shortens the qualification process for

sale into European markets. The driver out-

puts are also protected from overload and

shorts up to ±30V.

Single Supply, Low Power and Fast

The LT1780/LT1781 generate the

RS232 bias voltages internally. The internal

charge pump requires only four small 0.1µF

capacitors. The LT1780 has a shutdown

mode for power savings in battery-operated

applications while the LT1781 is in an indus-

try standard footprint. In shutdown, the

LT1780 current drain drops to just 1µA.

The LT1780/LT1781 operate at

250kBaud for high speed RS232 applica-

tions. The low power and dual transceiver

configuration make these devices ideal for

portable instruments that communicate

through an RS232 interface to the host com-

puter. 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.

0.1µF

LOGIC

INPUTS

LOGIC

OUTPUTS

ON/OFF 18

17 5V INPUT

OUT

–

OUT

RS232 OUTPUT

RS232 INPUT

1780/81 • TA01

LT1780

Figure 1. LT1780 in Single Supply

Application

LTC1542: Micropower Op Amp and Comparator

The LTC1542 combines a micropower

amplifier and comparator in one miniature

8-pin package (MSOP or SO). This circuit

has very low input offset voltage and low

standby current. The outputs swing rail-to-

rail. These features are useful for battery-

powered applications such as cellular

phones, keyless entry systems and remote

controllers where precision sensing and low

power consumption are required.

The circuit operates from a single 2.5V

to 12.6V or dual ±1.25V to ±6.3V supply

with a typical supply current of 5µA. Both

the op amp and the comparator have a com-

mon mode input voltage range that extends

from the negative supply to within 1.3V of

the positive supply. The input current is

10pA typically for both op amp and com-

parator.

The Op Amp

The input offset voltage of the op amp

is a very low 700µV maximum. The input

bias current is 1nA maximum over the

extended temperature range.

The op amp is internally compensated

to be unity-gain stable with typical gain-

bandwidth of 12kHz and slew rate of 8V/ms.

Unlike other micropower CMOS op amps,

the LTC1542 maintains stability in unity-

gain configuration even while driving heavy

capacitive loads of up to 1000pF.

The Comparator

The comparator has a high impedance dif-

ferential input stage. The CMOS output

stage can swing from rail to rail and source

up to 20mA. The output stage has been

designed to eliminate the power supply

glitches that normally occur when the output

changes logic state. In addition, ±3mV of

internal hysteresis ensures clean output

switching, even with slow moving input

signals.

The Family

The LTC1542 is the newest member of

the micropower building block family of

useful combinations of analog functions (see

Table 1).

–

1.2V

0.2V

1.182V

Table 1. Micropower Building Block

Family

Op Amp Comparator Reference

LTC1542

LTC1541

LTC1540

LT1635

–

The LTC1542 is a much improved

design, pin-compatible to existing circuits.

Try it in your battery- or solar-powered sys-

tem, local area detectors and alarms, infrared

receivers or smoke detectors and safety sen-

sors. 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.