slyt211.pdf
(
291 KB
)
Pobierz
Texas Instruments Incorporated
Power Management
Miniature solutions for voltage isolation
By Geoff Jones
(Email: gjones@ti.com)
Marketing Manager
The hot growth in distributed-power architecture has
fueled the development of miniature low-power (<2-W)
DC/DC converters. As their name implies, these devices
minimize the impact of the converter onboard space. They
provide point-of-use isolated power conversion for analog
circuitry in industrial applications and safety-critical appli-
cations such as telecommunications and medical equipment.
Additionally, miniature DC/DC converters benefit designers
who need galvanically isolated output power or noise
reduction in analog circuitry.
In most modern noise-sensitive circuitry, system designers
often have a small number of components that require
total isolation from their input power supply. It is neces-
sary to isolate the load and noise presented to the local
power-supply rails from the main-supply rails of the entire
system. Mixed-signal integrated circuit (IC) design, for
example, frequently leads to nonfunctional devices
because of noise problems. Large amounts of digital noise
combined with sensitive analog circuitry often results in
interference noise.
1
Miniature DC/DC converters with galvanic isolation offer
very low output noise and high accuracy. Galvanic isolation
helps to reduce system noise by providing a floating
ground on the secondary side of the converter.
2
The
input-to-output isolation can then be used to provide a
simple, isolated-output power source; or, it could be used
to generate different voltage rails, dual-polarity rails,
and/or nonstandard voltages. Also, as a noise reduction
technique in analog circuitry, the isolation barrier prevents
noise from the digital ground bus from affecting the sensi-
tive analog circuits.
The standard brick-type converter is not well suited for
this requirement. In addition to its higher cost, the brick’s
output power is overkill for applications requiring <2 W.
What’s more, the installed size of a brick is often prohibitive.
Designers require miniaturization to save valuable board
real estate. Because they are significantly smaller than
even the new sixteenth-brick format (0.29 in
2
vs. 1.17 in
2
),
miniature DC/DC converters are particularly suited to gen-
erating onboard voltages in space-constrained designs.
So why not “roll your own” DC/DC power supply? Discrete
component onboard converter designs are a low-cost alterna-
tive to bricks and off-the-shelf miniature DC/DC converters.
However, fewer designers are developing discrete designs
because of their disadvantages. Extra functionality, such as
device protection and module-to-module synchronization,
are difficult to implement; reliability is often poor; and
achieving a small-sized power supply is difficult. In addi-
tion, many designers of higher-level products—of which
the DC/DC converters are only one component—lack the
time to become expert enough in converter design to
build their own devices. As a result of these challenges,
more and more designers are specifying miniature DC/DC
converters for their applications. The converters offer
significantly lower risk, much faster time to market, and
development-cost savings.
Besides their advantages over bricks and discrete designs,
miniature DC/DC converters also provide a compact-sized
power solution for point-of-load (POL) power conversion.
POL converters enable designers to overcome the chal-
lenges caused by the high peak-current demands and
low-noise margins of the latest high-performance semicon-
ductor devices. The converters can be placed close to
their loads. This minimizes losses caused by voltage drops,
helps overcome noise sensitivity and EMI emission issues,
and ensures tight regulation under dynamic load conditions.
What’s available?
Miniature DC/DC converters offered by C&D Technologies,
Texas Instruments, Wall Industries, and others benefit
designers who require isolation and output current in the
20- to 500-mA range. The converters are available with
5-, 12-, 15-, or 24-V inputs. Single-output converters are
available with voltages from 3.3 to 24 VDC. Dual-output
converters with voltages from ±3.3 to ±24 VDC are also
available.
Miniature DC/DC converters offer regulated or unregulated
outputs with input-to-output isolation ratings of 1000,
1500, or 3000 VDC. Operating temperature extends from
–40°C to +100°C. Due to their high switching frequencies
(up to 400 MHz), the converters deliver efficiencies of up
to 85%.
Built-in features
For system designers seeking to implement miniature
DC/DC converters, the devices offer various built-in features
that ease system integration and simplify design. Many of
the available products incorporate thermal and short-circuit
protection and internal filtering. Some of the more advanced
converters allow device-to-device synchronization. If an
application uses more than one converter on a PC board,
13
Analog Applications Journal
3Q 2005
www.ti.com/aaj
Analog and Mixed-Signal Products
Power Management
Texas Instruments Incorporated
Figure 1. Self-synchronizing DC/DC converters in
distributed-power application
DCP010512B
+5 V
Isolated
I/O Modules
Support
Op Amp, ADC,
DAC, MCU, etc.
+12 V
SYNC
IN
Create +12-V/1-W
Output with
1000-V Isolation
5-V
Power
Supply
10 to
30 VDC
+5 V
DCR010505
Nonisolated
I/O Modules
Support
Op Amp, ADC,
DAC, MCU, etc.
–5 V
SYNC
IN
Create Isolated
–5-V/1-W Output
from +5-V Input
+5 V
beat frequencies and other electrical interference can be
generated. DCP010512B and DCR010505 converters
(Figure 1) overcome this problem with a built-in synchro-
nization control that allows multiple converters to be syn-
chronized to one another. The feature makes it easy for
designers to synchronize up to eight devices by connecting
the SYNC
IN
pins together. This eliminates electrical inter-
ference caused by variations in switching frequencies.
(Figure 2). They use an IC lead-frame as the medium to
interconnect silicon devices and magnetic components
within the IC package (Figure 3). The result is an isolated
DC/DC converter that provides high reliability, excellent
thermal management, small size, and compatibility with
standard board-assembly processes. The standard IC format
also allows tape-and-reel assembly, which helps reduce
manufacturing costs.
Construction
Today’s DC/DC converter technologies continue to focus
on higher densities and efficiencies as well as on smaller
packages. One of the more innovative converters is manu-
factured with the same technology as standard IC packages,
including dual-in-line (DIL) and small-outline (SO) styles
Figure 3. IC lead-frame
Figure 2. Miniature isolated DC/DC converter
in standard IC package
14
Analog Applications Journal
Analog and Mixed-Signal Products
www.ti.com/aaj
3Q 2005
Texas Instruments Incorporated
Power Management
Different configurations
The galvanic isolation of the output from a miniature
DC/DC converter allows nonstandard voltage rails to be
generated by connecting multiple converters in series. This
is accomplished by simply connecting the positive output of
one converter to the negative output of another. This con-
figuration allows a wide variety of voltage variations to be
produced. The outputs on some dual-output converters
can also be connected in series to provide two times the
magnitude of output voltage. Figure 4 shows a dual ±15-V
converter connected to provide a 30-V rail.
3
Multiple converters connected in parallel often provide
a suitable solution for cases where a single converter is
unable to deliver the required output power. When parallel
connection is used, it is always a good design practice to
use parallel converters of the same type. Figure 5 shows
two converters connected in parallel.
2
Addressing voltage isolation in
low-power applications
Miniature DC/DC converters that provide input-to-output
isolation and low output power offer innovative solutions
for high-density power-supply designs in a variety of appli-
cations. Some typical examples include industrial process
control, DC motor drive, test and measurement, power
transmission, medical equipment, and data acquisition.
Figure 4. Connecting dual-output converters
in series
+V
IN
+V
OUT
+15 V
DC/DC
Converter
5V
GND
30 V
–15 V
–V
IN
–V
OUT
Figures 6-8 show examples of DC/DC converters and
operational amplifiers (op amps) used in common power-
supply designs.
Positive-to-negative voltage conversion
Positive-to-negative voltage conversion is a popular applica-
tion for miniature DC/DC converters. Precision op amps are
optimized for higher-speed applications. The devices offer
very low offset voltage and drift and are commonly found
in data acquisition, telecom equipment, professional audio
equipment, and portable applications requiring high preci-
sion. Some op amps require complementary power-supply
Figure 5. Connecting multiple DC/DC converters in parallel
+V
IN
+V
OUT
DC/DC
Converter
SYNC
IN
–V
IN
–V
OUT
2x
Power
Out
+V
IN
+V
OUT
DC/DC
Converter
SYNC
IN
–V
IN
–V
OUT
15
Analog Applications Journal
3Q 2005
www.ti.com/aaj
Analog and Mixed-Signal Products
Power Management
Texas Instruments Incorporated
Figure 6. Positive-to-negative voltage from
single supply
Figure 7. Positive and negative voltage from
single supply
+5 V
DCP010512DB
DCP010505B
+12 V
+V
IN
+V
IN
GND
5V
–V
IN
–V
IN
–5 V
–12 V
–V
CC
+
+V
CC
–V
CC
+
+V
CC
OPAy7xx
OPA277
–
–
rails. The isolated output of the converter in Figure 6 is
used to generate a negative supply voltage. The isolated
negative output is referenced to the op amp’s positive input.
voltage range of 4.5 to 5.5 V, the converter performs a
boost function that creates a +12-V output and a buck-
boost function with a –12-V output.
Positive and negative voltage from a single supply
Miniature DC/DC converters in standard IC packaging
reduce the board space required to create positive and
negative output voltages to an op amp. Figure 7 shows the
ability of a single isolated converter to create positive-to-
negative output voltages efficiently for a signal conditioning
circuit with differential input. The dual-output converter is
used to create unregulated output voltages with a magni-
tude higher than its +5-V input. Operating from an input
Power-supply isolation for AC or DC
instrumentation amplifier
The challenge for system designers working with signal
conditioning circuits in AC or DC instrumentation amplifiers
is to eliminate ground loops that can affect measurement
accuracy. Miniature isolated DC/DC converters achieve
this goal. The circuit in Figure 8 uses a dual-output DC/DC
converter to produce an isolated voltage. The converter is
used in conjunction with a precision isolation amplifier to
Figure 8. Power-supply isolation for AC or DC
instrumentation amplifier
DCP021212D
+12 V
+V
IN
12 V
–12 V
–V
IN
Low-Cost
2-W Isolated
Converter
–
+
+V
CC
+V
CC
+V
CC
MUX
MUX
–V
CC
+
+
–V
CC
–V
CC
MPC
506
Input
INA101
OPA244
ISO122
–
–
16
Analog Applications Journal
Analog and Mixed-Signal Products
www.ti.com/aaj
3Q 2005
Texas Instruments Incorporated
Power Management
fully isolate the instrumentation from noise generated by
other parts of the circuit. The isolation barrier character-
istics do not affect the signal integrity, resulting in excel-
lent reliability and good high-frequency immunity across
the barrier.
Summary
In most modern noise-sensitive circuitry, system designers
often have a small number of components that require
total isolation from their input power supply. Miniature
DC/DC converters effectively isolate the load and noise
presented to the local power-supply rails from the main-
supply rails of the entire system.
The off-the-shelf devices use a highly integrated package
design that makes them suitable for a wide range of appli-
cations in space-constrained board designs. They are
smaller and lower-priced than the standard brick-type
converters. When compared to discrete designs, miniature
DC/DC converters offer lower risk, much faster time to
market, and development-cost savings.
References
For more information related to this article, you can down-
load an Acrobat Reader file at www-s.ti.com/sc/techlit/
litnumber
and replace
“litnumber”
with the
TI Lit. #
for
the materials listed below.
Document Title
TI Lit. #
1. “Noise Reduction is Crucial to Mixed-Signal
ASIC Design Success,”
Electronic Design
(October 30, 2000).
—
2. “Packaged DC-DC Converters Solve
Distributed Power Dilemmas,”
Electronic
Design
(June 12, 2000).
—
3. “Miniature, 2W Isolated Unregulated DC/DC
Converters,” DCP02 Series Datasheet . . . . . . .
.sbvs011
Related Web sites
power.ti.com
www.ti.com/sc/device/
partnumber
Replace
partnumber
with
DCP010512B,
DCP010512BD,
DCP021212D,
DCR010505,
INA101,
ISO122,
MPC506,
OPA244,
or
OPA277
17
Analog Applications Journal
3Q 2005
www.ti.com/aaj
Analog and Mixed-Signal Products
Plik z chomika:
TirNaNog
Inne pliki z tego folderu:
slyt331.pdf
(570 KB)
slyt333.pdf
(771 KB)
slyt335.pdf
(746 KB)
slyt332.pdf
(706 KB)
slyt334.pdf
(626 KB)
Inne foldery tego chomika:
ACE
AcornUser
AmigaComputing
AmigaFormat
AmigaShopper
Zgłoś jeśli
naruszono regulamin