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Volume 43, Number 4, 2009
A forum for the exchange of circuits, systems, and software for real-world signal processing
In This Issue
2
Editors’ Notes; New Product Introductions
3
Isolation in High-Voltage Battery Monitoring for Transportation Applications
6
Synchronizing Device Clocks Using IEEE 1588 and Blackfin Embedded Processors
11
Using Isolated RS-485 in DMX512 Lighting Applications
13
Designing High-Performance Phase-Locked Loops with High-Voltage VCOs
17
Adjustable-Gain Difference Amplifier Circuit Measures Hundreds of Volts, Rejects Large
Common-Mode Signals
19
Automobile Tail-Lamp and Brake-Lamp Controller
www.analog.com/analogdialogue
Editors’ Notes
PRODUCT INTRODUCTIONS: VOLUME 43, NUMBER 4
Data sheets for all ADI products can be found by entering the part
number in the search box at www.analog.com.
IN THIS ISSUE
Isolation in High-Voltage Battery Monitoring for Transportation
Applications
Battery stacks for transportation can provide hundreds of volts.
These high voltages can prove lethal to human beings—and even
lower voltages can damage electronic equipment—so safety is a
key concern. Although these stacks are inherently dangerous,
they must still communicate with the cell-monitoring electronics.
Galvanic isolation is thus required to make the communications
method safe and reliable. Page 3.
October
Ampliier
, instrumentation, micropower ..............................
AD8235
Controller
, dc-to-dc, step-down, 2-output ........................
ADP1877
Sensor
, inertial, six-degrees-of-freedom ..........................
ADIS16362
Supervisor
, voltage, 4-channel,
±
supplies .......................
ADM12914
November
ADC
, SAR, 16-bit, 2.5-MSPS ..............................................
AD7985
ADC
, SAR, 16-bit, 10-MSPS, 1.5-LSB INL ........................
AD7626
Ampliier
, operational, quad, rail-to-rail .......................
ADA4692-4
DAC
, TxDAC+, dual, 16-bit, 1.2-GSPS ................................
AD9122
Gain Blocks
, RF/IF, 4-GHz ..............................
ADL5601/ADL5602
Generator
, clock, 10-output, Ethernet ..................................
AD9571
Gyroscope
, yaw-rate, digital-output ...............................
ADIS16265
Power Supply
, 1.2-A, 16-bit level-setting DACs ...................
AD5560
Regulator
, low-dropout, 150-mA ........................................
ADP150
Regulator
, low-dropout, dual, 200-mA .............................
ADP5030
Transceiver
, RS-485, 16-Mbps, full-duplex ...................
ADM1490E
Synchronizing Device Clocks Using IEEE 1588 and Blackin
Embedded Processors
IEEE 1588 deines a protocol to synchronize distributed clocks
on a network. The preferred clock synchronization method for
many applications, it is cost-effective, supports heterogeneous
systems, and provides nanosecond-level synchronization. The
ADSP-BF518 Blackin
®
processor includes dedicated hardware
support for IEEE 1588. This article shows clock synchronization
performance obtained using this solution. Page 6.
December
Ampliier
, difference, dual, gain of ½ or 2 ............................
AD8279
Ampliier
, difference, precision, high-voltage .......................
AD8209
Ampliier
, operational, micropower, rail-to-rail ..............
ADA4051-1
Ampliier
, operational, zero crossover distortion ..................
AD8505
Ampliier
, ultralow-noise, dual, selectable gain ....................
AD8432
ADC
, SAR, 14-bit, 2.5-MSPS ..............................................
AD7944
ADC
, sigma-delta, 8-channel, 24-bit, 4.8-kHz .....................
AD7194
ADCs
, pipelined, 10-/12-/14-bit,
80-MSPS ...............................................
AD9609/AD9629/AD9649
ADCs
, pipelined, 14-/16-bit, 125-MSPS .................
AD9255/AD9265
Codecs
, audio, stereo, 24-bit, 96-kHz ..........
ADAU1381/ADAU1382
Controller
, digital, isolated power supply .........................
ADP1043A
Controllers
, synchronous buck, 20-V ................
ADP1872/ADP1873
Driver
, current/voltage, programmable .................................
AD5751
Driver
, laser-diode, differential, 11.3-Gbps .......................
ADN2531
Drivers
, MOSFET, dual 2-A .............
ADP3629/ADP3630ADP3631
Filter
, video, 6-channel, SD/ED/HD .............................
ADA4424-6
Gyroscopes
, yaw-rate, digital-output ...........
ADIS16260/ADIS16265
Isolators
, digital, 4-channel, 1-kV rms isolation ..............
ADuM744x
Mixer
, balanced, 500-MHz to 1700-MHz .........................
ADL5367
Mixer
, balanced, 1200-MHz to 2500-MHz .......................
ADL5365
Mixer
, balanced, dual, 1200-MHz to 2500-MHz ..............
ADL5356
Multiplexer
, CMOS, 4-channel, differential, 4.5-
Ω
..........
ADG1439
Multiplexer
, CMOS, 8-channel, 9.5-
Ω
..............................
ADG1438
Multiplexer
, CMOS, 8-channel, differential, 4.5-
Ω
..........
ADG1607
Multiplexer
, CMOS, 16-channel, 4.5-
Ω
............................
ADG1606
Prescaler
, divide-by-4, 4-GHz to 18-GHz ........................
ADF5001
Receivers
, IF, dual/quad .......................................
AD6642/AD6657
Regulators
, very-low-dropout, 300-mA ...............
ADP122/ADP123
Reset Circuits
, microprocessor,
ultralow-power ..............................................
ADM632x/ADM634x
Rheostats
, digital, 1024-/256-position, 1% accuracy ............
AD527x
Switch
, digital crosspoint, 4.25-Gbps, 16
×
16 ..................
ADN4604
Switch
,
i
CMOS, octal SPST, 9.5-
Ω
...................................
ADG1414
Switch
,
i
CMOS, SPDT, 2.1-
Ω
...........................................
ADG1419
Switches
,
i
CMOS, dual SPST, 2.1-
Ω
.................................
ADG142x
Switches
,
i
CMOS, SPST, 1-
Ω
..........................
ADG1401/ADG1402
Transceiver
, multiband, 3G femtocell ...............................
ADF4602
Transceivers
, RS-485,
isolated signal and power ..........................
ADM2582E/ADM2587E
Using Isolated RS-485 in DMX512 Lighting Applications
Theatrical lighting applications have evolved from lanterns in
open-air theaters into the more complex systems available today.
Modern lighting equipment includes dimmers, lashing lights,
moving lights, colored lights, and gobos. These lighting systems
are often controlled over long distances—up to 4000 feet—using
the DMX512 communications protocol. Page 11.
Designing High-Performance Phase-Locked Loops with
High-Voltage VCOs
Phase-locked loops are used to provide the local oscillator in
radio receivers and transmitters; for clock distribution and
noise reduction, and as the clock source for high-sampling-rate
ADCs. This article considers the basics of PLLs, examines the
current state of the art in PLL design, discusses pros and cons
of typical architectures, and introduces some alternatives to
high-voltage VCOs. Page 13.
Adjustable-Gain Difference Ampliier Circuit Measures Hundreds
of Volts, Rejects Large Common-Mode Signals
To monitor power-line voltages or other large signals, a differential
ampliier in a feedback loop with an inverting op amp is useful
for measuring differential signals up to 500 V. This circuit also
rejects large common-mode voltages and allows the differential
gain to be set by a ratio of resistors, enabling the user to select the
level of attenuation. Page 17.
Automobile Tail-Lamp and Brake-Lamp Controller
Light emitting diodes (LEDs) are recently f inding uses in
automobiles, where they provide signaling, daytime running
lights, and interior lighting. As this technology hits the road,
manufacturers continue to investigate new ways to apply it, taking
advantage of the styling possibilities afforded by LED headlights
and taillights. Page 19.
Analog Dialogue
,
www.analog.com/analogdialogue
, the technical magazine of
Analog Devices, discusses products, applications, technology, and techniques
for analog, digital, and mixed-signal processing. Published continuously
for 43 years—starting in 1967—it is currently available in two versions.
Monthly editions offer technical articles; timely information including recent
application notes, new-product briefs, pre-release products, webinars and
tutorials, and published articles; and potpourri, a universe of links to important
and relevant information on the Analog Devices website,
www.analog.com
.
Printable quarterly issues feature collections of monthly articles. For history
buffs, the
Analog Dialogue
archive includes all regular editions, starting with
Volume 1, Number 1 (1967), and three special anniversary issues. If you wish
to subscribe, please go to
www.analog.com/analogdialogue/subscribe.html
.
Your comments are always welcome; please send messages to
dialogue.
editor@analog.com
or to
Dan Sheingold
, Editor [
dan.sheingold@analog.com
]
or
Scott Wayne
, Publisher and Managing Editor [
scott.wayne@analog.com
].
Dan Sheingold
[
dan.sheingold@analog.com
]
Scott Wayne
[
scott.wayne@analog.com
]
ISSN 0161-3626 ©Analog Devices, Inc. 2011
2
Isolation in High-Voltage
Battery Monitoring for
Transportation Applications
of window comparators. It is beyond the scope of this article to
discuss these products in any depth, but it is worth noting how such
devices communicate in a stack coniguration. Each cell establishes
the common-mode level for the measurement input from the one
above it. A daisy-chain interface allows each individual AD7280 in
a stack to communicate directly with the next AD7280 above it or
below it (and thus pass digital information up or down the stack)
without needing isolation. The SPI interface of the bottommost
AD7280 is used to exchange data and control signals for the
whole stack with the system microcontroller. It is at this point that
high-voltage galvanic isolation must be employed to protect the
low-voltage electronics elsewhere in the system.
By John Wynne
Cars with wheels driven by battery-powered electric motors,
continuously or intermittently, have become a hot topic. These
“green” vehicles rely on batteries of series-connected cells to obtain
suficiently high voltage to operate the motor eficiently. Such
high-voltage (HV) stacks are used in
all-electric vehicles
(EV)—as
well as
hybrid electric vehicles
(HEV), which rely on an internal-
combustion engine (ICE) for charging and (in many cases) shared
propulsion. EVs must be plugged into a power source for charging;
some newer hybrids are designed as
plug-in hybrid electric vehicles
(PHEV), which are considered to be essentially EVs with an ICE
for range extension.
HV stacks are already used in many industries and applications
outside of the transportation industry—typically in uninterruptible
power supplies (UPS) to store energy from the grid in dc form;
as emergency dc supplies in 48-V communications equipment; as
emergency supplies in crane and lift systems; and in wind turbines
for feathering the blades in an emergency. Although we discuss
here the use of battery stacks in vehicles, the underlying issues are
common to all types of stacks.
Battery stacks for transportation can typically involve 100 or more
cells, providing hundreds of volts. Since it is generally accepted
that more than 50 V or 60 V can prove lethal to human beings,
and even lower voltages can damage electronic equipment—
considering the stability concerns about cells using some types of
electrochemical reactions—safety is a key concern. Although these
stacks are inherently dangerous, they must still communicate with
the cell monitoring electronics, which are usually located within
the battery enclosure. Thus, the communications method must
be safe and reliable.
CELL
MONITOR
BIDIRECTIONAL
DAISY-CHAIN BUS
BETWEEN PACKS
CELL
MONITOR
ISOLATION
SAFETY
SWITCH
CELL
MONITOR
BIDIRECTIONAL
COMMUNICATION BUS
CAN
BUS
MICROPROCESSOR
WITH CAN
CONTROLLER
CELL
MONITOR
ISOLATION
Organizing Cells in HV Stacks
The original equipment manufacturer generally speciies the
physical packing of the cells into enclosures called
packs
, which
typically contain from six to 24 cells in series. Packs containing
large numbers of cells are physically larger and more awkward to it
into typical vehicle spaces. The cell-monitoring integrated circuits
associated with the cells are physically close to the monitored
cells and are powered by the cells themselves. Whether it is
essential to monitor the voltage of each cell depends on the cell
chemistry. For instance, the behavior of HV stacks based upon
nickel-metal hydride
(NiMH) chemistry is very well understood,
and generally no effort is made to measure individual cell voltages;
it is suficient to measure the total voltage of all the cells within
a particular pack. With stacks based upon
lithium-ion
(Li-Ion)
chemistry, however, it will be necessary to monitor the voltage
of each cell to detect an over- or undervoltage condition on any
individual cell in the string. It is not generally necessary to measure
the temperature of each Li-Ion cell, but the facility to do so should
be available. The electronics for monitoring a NiMH stack are thus
considerably simpler than those for a Li-Ion stack. Figure 1 shows
a common approach to building and monitoring an HV stack.
Cell-monitor ICs typically handle six or 12 cells. Currently, two
application-speciic special-purpose (ASSP) products are available
from Analog Devices for cell monitoring: the
AD7280
,
1
intended
for use as a primary monitor, is based on a high-speed multiplexed
12-bit analog-to-digital converter; another device, intended
for use as a backup, or redundancy monitor, is based on a series
CURRENT
SHUNT
SIGNAL
CONDITIONING
SIGNAL
REPRESENTING
STACK CURRENT
ISOLATION
Figure 1. Serial cell monitoring and isolation in a battery stack.
In Figure 1, the string of serially connected cells has a switch or
contactor placed in the middle of the string. Normally, this switch
is closed at all times, whether the vehicle is in normal operation or
parked. For vehicle maintenance or in emergency situations the
switch is physically pulled or removed from its position to disable
the stack voltage from appearing at the stack terminals. In order
not to compromise the isolation provided by the open switch,
it is important not to have any electronic components bridging
the switch terminals. Thus, the top half of the stack should be
electrically isolated from the bottom half with the switch open.
This means that cell data from the top half of the stack must be
communicated via its bottommost cell monitor across an isolation
barrier to the microprocessor or microcontroller that is managing
the low of data into and out of the complete stack. Similarly,
the bottom half of the stack must also be isolated from this
microprocessor or microcontroller, so it has an identical isolation
barrier to that of the top half.
In addition to the cell monitors, a current monitor is positioned
somewhere in the stack to measure and report on the stack
current. This monitor is generally placed at the bottom of the
stack; it also needs to be considered for isolation. Hall-effect
Analog Dialogue Volume 43 Number 4
3
current sensors have inherent galvanic isolation and need no
further isolation circuitry. If, however, the current sensor uses a
shunt element, the associated shunt monitor circuitry will require
an individual isolation barrier. Current sensing using shunts
is becoming very popular; it is much more stable and accurate
than, yet price competitive with, Hall-effect sensing. The
use of low-value shunt resistors with low-cost high-resolution
monitoring electronics—such as the AD820x and AD821x
families of AEC-Q100 qualiied current shunt monitors, which
have shipped over 100M channels into automotive sockets to
date—minimizes self-heating, a traditional objection to this
approach. Thus, the system in Figure 1 requires three separate
isolation barriers, unless the current-sense monitor can feed into
the bottommost cell monitor, sharing its isolation barrier.
Another popular approach to organizing cells in a battery stack is to
group the battery packs into a series of electrically separate clusters
(Figure 2). The bottommost monitor of each cluster communicates
the local cell conditions across a dedicated isolation barrier back
to the microcontroller on the nonisolated side.
discharges or surges to enter a piece of equipment—and for
interfering signals to escape, either by conduction of the spurious
signals on the I/O lines or by radiation from the I/O cable. Adding
more cables to a battery stack can reduce its EMC performance
signiicantly unless careful attention is paid to the robustness of
the signals and the communication protocol chosen. Because of
this, the EMC performance of the I/O device connected to the
port is crucial to the EMC of the entire equipment.
The popular SPI communication protocol is suitable for
communicating between devices on the same printed circuit board
(PCB); but single-ended signals can be dificult to transmit reliably
over 24 to 36 inches of wire, especially in a noisy environment.
Where digital signals are to be transmitted off board, prudent system
design might include differential transceivers, such as the
ADM485
.
These transceivers can be powered from the low-side power source,
so no power is drawn directly from the cells in the stack.
Isolation Technology Is Key to Stack Communications
For battery stack voltages to get higher in order to satisfy the
demands of higher power electric motors found in heavier
private vehicles, as well as light delivery trucks and vans, the
number of cells in battery stacks must increase. In addition to
increased numbers of serially connected cells, many battery
packs now contain paralleled strings of cells in order to
increase the ampere-hour (AH) capacity of the overall battery
pack. The cells of each parallel string must be monitored—
resulting in the collection of a lot of data. The cell monitor
data associated with all of these cells must be transmitted
back to the battery-measuring-system (BMS) microcontroller
reliably and within the system loop time requirements set by
the system integrators.
Accordingly, the dificulties associated with providing reliable data
communications across system-to-system boundaries have also
increased. A key element to providing reliable communications across
so many isolated boundaries inside a typical battery stack is
automotive-
qualiied isolation technology
, now available from Analog Devices.
The basis of the technology is
magnetic isolation
, with transformers
fabricated in a planar fashion using cost-effective standard CMOS
processes (see Figure 3). This facilitates the integration of multiple
isolation channels into a single component—or the integration of
isolation channels with other semiconductor functions, such as line
drivers and analog-to-digital converters (for example, the
AD7400
isolated
∑
-
∆
modulator).
CELL
MONITOR
ISOLATION
ISOLATED
COMMUNICATION BUS
CELL
MONITOR
ISOLATION
SAFETY
SWITCH
CELL
MONITOR
ISOLATION
CAN
BUS
MICROPROCESSOR
WITH CAN
CONTROLLER
CELL
MONITOR
ISOLATION
V
DD1
GND
1
V
IA
V
IB
V
OC
V
OD
V
E1
GND
1
V
DD2
GND
2
V
OA
V
OB
V
IC
V
ID
V
E2
GND
2
1
2
3
16
15
14
CURRENT
SHUNT
SIGNAL
CONDITIONING
SIGNAL
REPRESENTING
STACK CURRENT
ISOLATION
ENCODE
DECODE
4
ENCODE
DECODE
13
Figure 2. Battery stack with parallel access to packs.
DECODE
ENCODE
5
12
The increased use of digital isolators makes this approach
somewhat more expensive than the system shown in Figure 1, but
it offers the possibility of reading back all the cell data in a much
shorter time, with all cell clusters simultaneously being asked
to report on what the cell monitors are seeing within the packs.
Another important beneit is that it allows backup monitoring to
continue in the presence of problems developing with the daisy
chain, such as broken wires or poor connector contacts. The data
from “off-the-air” packs can still be determined by correlating the
remaining pack voltages with the overall stack voltage.
It does require more cabling, which can be problematic, since
up to 75% of
electromagnetic-compatibility
(EMC) problems are
considered to occur in relation to input/output (I/O) ports. The I/O
port is an open gateway for electrostatic discharges or fast transient
DECODE
ENCODE
6
7
11
10
9
8
Figure 3. Functional block diagram of
ADuM1402
quad isolator.
These
i
Coupler
®
digital isolators that, unlike optocouplers, do
not degrade over the lifetime of the vehicle can accommodate
the harsh operating conditions often encountered through the
changing seasons. The recently released family of devices listed in
Table 1—AEC-Q100 qualiied to 125
°
C—uses the same materials
as its well-established counterparts in the ADI family of
i
Coupler
products, with more than 300 million channels of isolation shipped
to date. The 2-channel, 3-channel, and 4-channel digital isolator
4
Analog Dialogue Volume 43 Number 4
Table 1. AEC Q100-Qualiied
i
Coupler Isolators
Output
Reverse
Direction
Options
Total
Number
of
Channels
Max
Data
Rate
(Mbps)
Max
Propagation
Delay (ns)
Supply
Range
(V)
Max
Temperature
(°C)
Price
($U.S.)
Part Number
Default EN
Package
0
1
2
H
L
Z
2.5 kV rms Isolation
ADuM120xA/WS
•
—
1
150
•
— — 3.0 to 5.5
125
8-lead SOIC_N
1.21/2.13
•
ADuM120xB/WT
2
•
—
10
50
•
— — 3.0 to 5.5
125
8-lead SOIC_N
1.76/3.11
•
ADuM120xC/WU
•
—
25
45
•
— — 3.0 to 5.5
125
8-lead SOIC_N
2.44/4.30
•
ADuM130xA/WS
•
—
1
100
•
—
•
3.0 to 5.5
125
16-lead SOIC_W 1.61/2.42
•
3
ADuM130xB/WT
•
—
1
32
•
—
•
3.0 to 5.5
125
16-lead SOIC_W 2.42/3.62
•
ADuM140xA/WS
1
100
•
—
•
3.0 to 5.5
125
16-lead SOIC_W 2.15/3.22
•
•
•
4
ADuM140xA/WS
10
50
•
—
•
3.0 to 5.5
125
16-lead SOIC_W 2.22/4.82
•
•
•
families in the table have data rates up to 25 Mbps and propagation
delays as low as 32 ns.
The planar transformers are inherently bidirectional; therefore,
signals can pass in either direction. All possible combinations of
drive and receive channels within the total number of channels are
available. For instance, the 2-channel ADuM120xW, 3-channel
ADuM130xW, and 4-channel ADuM140xW, alone or together,
offer seven different channel conigurations (4-0, 3-1, 2-2, 3-0,
2-1, 2-0, 1-1), ensuring an optimized solution for all situations.
Figure 4 summarizes the various conigurations available.
Two of the most distinguishing features of the
i
Coupler technology
are the ability to support high data rates and to operate with low
supply currents. The supply current drawn by an
i
Coupler channel
is largely a function of the data rate it is carrying. For 3-V operation,
the total power supply current—for both sides and all four channels
of the ADuM140xWS—is 1.6 mA typical (4 mA maximum) at a
data rate up to 2 Mbps. Low-power operation is important since,
on the isolated or “hot” side of the ADuM140xWS, the power
comes from the cells themselves through a voltage regulator. The
monitors are also powered from this same voltage source, so the less
power taken by all elements of the monitoring and communicating
circuitry the better. All isolation products are available in small,
low-proile, surface-mount 8-lead SOIC_W or 16-lead SOIC_W
packages and come with safety certiications from UL, CSA, and
VDE. They feature isolation ratings up to 2.5 kV rms and working
voltages up to 400 V rms.
i
Coupler Technology Begets
iso
Power Devices: Integrated,
Isolated Power
One of the most exciting developments of
i
Coupler technology is
the integration of both power transmission and signal transmission
within the same package. With microtransformers similar to those
used for signal isolation, power can now be transferred across an
isolation barrier—allowing fully integrated isolation for remotely
powering the data isolators in the battery packs. Local power is
supplied to an oscillating circuit that switches current through a
chip-scale air core transformer. Power transferred to the isolated
side is rectiied and regulated to either 3.3 V or 5 V. The isolated-
side controller provides feedback regulation of the output by
creating a PWM control signal that is sent back to the local side
by a dedicated
i
Coupler data channel. The PWM control signal
modulates the oscillator circuit to control the power being sent to
the isolated side. The use of feedback permits signiicantly higher
power and eficiency.
The
ADuM540xW
devices are 4-channel digital isolators that
include an
iso
Power
®
, integrated, isolated dc-to-dc converter, which
provides up to 500 mW of regulated, isolated power at either 5.0 V
from a 5.0-V input supply or 3.3 V from a 3.3-V supply. As with
the standard
i
Coupler devices, a variety of channel conigurations
and data rates is available. Because an
iso
Power device uses
high-frequency switching elements to transfer power through its
transformer, special care must be taken during PCB layout to
meet emissions standards. Refer to
AN-0971
Application Note,
Recommendations for Control of Radiated Emissions with isoPower
Devices
, for details on board-layout considerations.The ADuM540x
family is currently undergoing AEC-Q100 qualiication.
References
1
Informat ion on al l ADI components can be found at
www.analog.com
.
Author
John Wynne
[
john.wynne@analog.com
] is a precision converter
marketing manager at Analog Devices.
ADuM1200W ADuM1201W
ADuM1400W ADuM1402W
Figure 4. Seven different conigurations with the ADuM120xW/ADuM130xW/ADuM140xW.
ADuM1300W ADuM1301W
ADuM1401W
Analog Dialogue Volume 43 Number 4
5
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