LINEAR TECHNOLOGY LT1494 User Manual

L DESIGN FEATURES

Consider New Precision Amplifiers for
Updated Industrial Equipment Designs

Introduction

Industrial equipment is designed for
long life cycles, so the electronic com­ponents used in industrial applications
are often chosen with significant em­phasis on proven performance, quality
and reliability. Precision amplifiers are
no exception. Even if new and innova­tive amplifiers become available over a
product’s lifetime, a redesigned board
is often built using the same proven
op amps in the old board. Even for
entirely new applications, designers
will choose amplifiers that have proven
their mettle in other circuits, making a
choice based more on familiarity than
performance.

Although an amplifier may have
been tried and proven in a design, it
is not necessarily the best solution for
every new design. Many can benefit
from using more recently released
amplifiers, which can improve overall
system performance, reduce power
consumption, shrink the board real
estate and expand the capability of
the system while reducing component
count.

Table 1 shows is a list of high per­formance amplifiers and their features.
Many are pin compatible with older
amplifiers, making it easy to swap
them into existing designs to update
industrial applications.

Table 1. Comparison of old and new high performance industrial amplifiers

Industry

Standard

Amplifiers

LT1078
LT2078

LT1012
LT1097

LT1112
LT1114

LT1494

LT1008

LT1055 Family

LT1169

LT1013
LT1014

Features

❏ Precision
❏ Micropower
❏ Single Supply

❏ Precision
❏ Low Noise
❏ Stable with any C-Load

❏ Low Power
❏ Matching Specs
❏ C-Load Stable

❏ Ultralow Power
❏ Rail-to-Rail
❏ Precision

❏ Picoamp Input

Bias Current

❏ Low Offset

Alternative

Amplifiers

LTC6078*

LT1880

LT1881 Family
LT6010 Family

LT6003*

LTC6240 Family*
LTC6084 Family*
LTC6088 Family*

LT1490A
LT1491A

by Brian Black

Feature

Improvements

❏ Higher Precision
❏ Lower Noise
❏ Faster

❏ Rail-to-Rail Out

❏ Higher Precision
❏ Rail-to-Rail Out

❏ Lower Power
❏ Lower Supply

Range

❏ Smaller Package

❏ Lower Power
❏ Lower Noise
❏ Higher Precision
❏ Faster
❏ Rail-to-Rail Out

❏ Rail-to-Rail In/Out
❏ Over-The-Top
❏ Lower Noise

Old and New Amplifiers Go
Head-to-Head

What follows is a comparison of some
old and new amplifiers, where the
new can easily be swapped in for the
old. Figures 1 and 2 show two ap­plications that can benefit from the
updated features offered in recently
released amps.

Rugged LT1494 vs
Miniscule LT6003

The LT1494 (introduced in 1997) is a
precision micropower (375µV offset
voltage at 1.5µA supply current) rail­to-rail input and output amplifier ideal

16

❏ Low Noise

LT1028

LT1007
LT1037

LT1124 Family

LTC1050

Family

* Maximum supply voltage is lower than predecessor

❏ Low Drift
❏ Unity Gain Stable

❏ Low Noise

❏ Low Noise
❏ Low 1/f Corner
❏ Precision

❏ Zero Drift
❏ No External Capacitors

LT6200 Family*
LT6230 Family*

LT1677 Family

LT6202 Family*
LT6233 Family*

LTC2050 Family*

Linear Technology Magazine • September 2009

❏ Lower Power
❏ Faster
❏ Rail-to-Rail In/Out

❏ Rail-to-Rail In/Out

❏ Lower Power
❏ Lower Noise
❏ Faster
❏ Rail-to-Rail In/Out

❏ Shutdown
❏ Lower Offset/Drift

DESIGN FEATURES L

+

–

0V TO 10V

INPUT

10kHZ

TRIM

5k

4.7k
15V

2N3906

15V

–15V

–15V

= 1N4148

3M

0.001 (POLYSTYRENE)

0.1MF

THE LOW OFFSET VOLTAGE OF LT1056
CONTRIBUTES ONLY 0.1Hz OF ERROR
WHILE ITS HIGH SLEW RATE PERMITS
10kHz OPERATION.

0.1MF

22k

75k

1.5k

LM329

3.3M

7

6

4

3

2

33pF

*1% FILM

OUTPUT
1Hz TO 10kHz

0.005%
LINEARITY

LT1056

Table 2. LT1056 vs LTC6240HV

Feature: LTC1056 LTC6240HV

Rail-to-Rail Outputs NO

Minimum Supply Voltage 10V

Maximum Supply Voltage

Single Supply NO

Supply Current 7mA

V

OS

I

B

Noise Voltage Density 22nV/√Hz

GBW 5.5MHz

Slew Rate

Settling Time

for low power battery operated ap­plications. Its rugged design includes
reverse battery protection along with
Linear Technology’s Over -The-Top

®

feature, which allows inputs to oper­ate above the voltage rails without
affecting the amplifier.

For handheld systems where reduc­ing space and extending battery life
are top design priorities, the LT6003

Linear Technology Magazine • September 2009

Figure 1. Precision: 1Hz to 10kHz voltage-to-frequency converter

L

YES

L

2.8V

L

40V

12V

L

YES

L

3.3mA

800µV

150pA

L

250µV

L

1pA

L

10nV/√Hz

L

18mHz

L

14V/µs

L

600ns

10V/µs

900ns

can be swapped for the LT1494.
The LT6003 is designed specifically
with handheld devices in mind with
higher integration, a smaller package,
and a lower supply voltage than the
LT1494.

The LT6003 also has a lower mini­mum supply voltage, 1.6V vs 2.2V for
the LT1494. This feature allows the
LT6003 to operate on a wider range

of supplies and allows for a deeper
discharge of alkaline batteries (known
for the steep dropoff in battery voltage
when depleted). The LT6003 further
extends battery life with a lower sup­ply current of 1µA vs 1.5µA for the
LT1494. Consistent rail-to-rail inputs
and outputs preserve dynamic range
even at low supply voltages.

Furthermore, the LT6003 is offered
in a tiny 2mm × 2mm DFN package,
which is three times smaller than the
LT1494’s MSOP package. The LT1494
still has the advantage of higher
maximum supply voltage of up to 36V
vs the 18V of the LT6003. Also, the
Over-The-Top inputs of the LT1494
make it a great choice for applications
in which the inputs may go above the
positive supply.

The LT1677 Updates the LT1007
with Rail-to-Rail Inputs and
Outputs

The LT1007, introduced in 1985 as
one of Linear Technology’s first prod­uct releases, is a precision low noise
40V amplifier with a great combina­tion of DC performance, high gain,
and low noise performance, making
it ideal for small signal applications.
However, since neither the inputs
nor the outputs are rail-to-rail, the
designer must take care to consider
the headroom required for the part to
function properly. Systems that can
benefit from rail-to-rail inputs and
outputs as a way to increase dynamic
range, to reduce the supply voltage,
or to eliminate the negative supply
rail altogether, should consider using
the LT1677.

The LT1677 is a single supply
drop-in update to the LT1007 with the
added benefits of rail-to-rail inputs and
outputs. An important feature in low
voltage (as low as 3V), single-supply
applications is the ability to maximize
the dynamic range. The LT1677’s input
common mode range can swing 100mV
beyond either rail and the output is
guaranteed to swing to within 170mV
of either rail. This rail-to-rail benefit
comes with minimal impact on noise
and DC precision.

17