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
L DESIGN FEATURES
–
+
–
+
S S
S
INVERTING
INPUT
1M
2
3
1
6
5
7
A
1/2 LT1078
10.1k 1M
10.1k
NONINVERTING
INPUT
B
1/2 LT1078
4
8
3V (LITHIUM CELL)
S
OUT
–
+
The LT1112 and LT1114 vs LT1881
Family and LT6010 Family
The LT1112 and LT1114 have a wide
supply range of 2V to 40V, high precision and very low noise; there is
not much missing from these older
standards. An alternative to these
parts is the LT1881 family, which adds
rail-to-rail outputs. The LT1881 family
brings the performance of the LT1112
to applications that need the wide
dynamic range. Another option is the
LT6010 family, which achieves higher
precision than the LT1112/LT1114
and includes rail-to-rail outputs. It
is especially attractive for low power
applications due to its lower supply
current and shutdown capability.
Conclusion
Amplifiers are highly versatile building
blocks that can often be reused from
one system design to the next, which
can simplify redesign. The pitfall of
reuse is that designers can miss out on
the benefits offered by newer amplifiers, sometimes settling for sub-optimal
performance, higher costs and larger
system size, when a better solution is
just as easy to use. Not only are most
of the newer devices pin-to-pin functional equivalents, they offer additional
benefits such as lower power, smaller
size, or rail-to-rail outputs which can
help next generation designs achieve
longer battery life, better precision and
smaller form factors.
L
Table 3. LT1078 vs LTC6078
Feature: LT1078 LTC6078
Rail-to-Rail Outputs NO
Minimum Supply Voltage
Maximum Supply Voltage
L
2.3V
L
44V
Shutdown Mode NO
Supply Current
V
OS
I
B
L
50µA
120µV
10nA
Noise Voltage Density 28nV/√Hz
GBW 200kHz
Figure 2. AC speed: single battery, micropower, gain = 100 instrumentation amplifier
L
YES
2.7V
6V
L
YES
72µA
L
25µV
L
1pA
L
16 nV/√Hz
L
750kHz
LTC2978, continued from page 5
tion has been selected, the designer
can save the parameters to a file and
upload it to the LTC factory. LTC can
use the file to pre-program parts, thus
allowing the customer to bring up their
boards with minimum hassle.
The LTC2978 utilizes the industry
standard PMBus interface protocol
which is a superset of the I2C compatible SMBus standard. PMBus is an
open and widely adopted standard that
clearly defines the protocols for digital power management of individual
DC/DC POL converters. The LTC2978
supports a large number of the PMBus
commands. It also features a number
18
of DC/DC converter manufacturerspecific commands to keep complexity
low and versatility high.
configuration to the LTC factory. From
this, Linear Technology can provide
ready-to-use, pre-programmed devices, customized for the particular
Conclusion
With its unprecedented parametric accuracy, rich feature set, and modular
architecture, the LTC2978 is an ideal
solution for managing large arrays of
DC/DC POL converters.
The industry standard PMBus interface, free PC-based graphical setup
software, and integrated EEPROM
make it easy to customize the LTC2978
for any application. Designers can
use the PC-based graphical interface
application.
Other features include an integrated
precision reference, a multiplexed
15-bit ∆Σ ADC, eight 10-bit voltagebuffered IDACs, eight overvoltage and
undervoltage 10-bit voltage supervisors with programmable thresholds
and response times, and an integrated
EEPROM for storing configuration
parameters and fault-log information.
The LTC2978 is offered in a 64-lead
9mm × 9mm QFN package.
L
to configure a device and upload the
Linear Technology Magazine • September 2009
Loading...