AD AD210 Precision, wide bandwidth 3-port isolation amplifier Datasheet

a
FEATURES
High CMV Isolation: 2500 V rms Continuous
63500 V Peak Continuous
Small Size: 1.00" 3 2.10" 3 0.350"
Three-Port Isolation: Input, Output, and Power
Low Nonlinearity: 60.012% max
Wide Bandwidth: 20 kHz Full-Power (–3 dB)
Low Gain Drift: 625 ppm/8C max
High CMR: 120 dB (G = 100 V/V)
Isolated Power: 615 V @ 65 mA
Uncommitted Input Amplifier
APPLICATIONS
Multichannel Data Acquisition
High Voltage Instrumentation Amplifier
Current Shunt Measurements
Process Signal Isolation
GENERAL DESCRIPTION
The AD210 is the latest member of a new generation of low
cost, high performance isolation amplifiers. This three-port,
wide bandwidth isolation amplifier is manufactured with surface-mounted components in an automated assembly process.
The AD210 combines design expertise with state-of-the-art
manufacturing technology to produce an extremely compact
and economical isolator whose performance and abundant user
features far exceed those offered in more expensive devices.
The AD210 provides a complete isolation function with both
signal and power isolation supplied via transformer coupling internal to the module. The AD210’s functionally complete design, powered by a single +15 V supply, eliminates the need for
an external DC/DC converter, unlike optically coupled isolation
devices. The true three-port design structure permits the
AD210 to be applied as an input or output isolator, in single or
multichannel applications. The AD210 will maintain its high
performance under sustained common-mode stress.
Providing high accuracy and complete galvanic isolation, the
AD210 interrupts ground loops and leakage paths, and rejects
common-mode voltage and noise that may other vise degrade
measurement accuracy. In addition, the AD210 provides protection from fault conditions that may cause damage to other
sections of a measurement system.
PRODUCT HIGHLIGHTS
The AD210 is a full-featured isolator providing numerous user
benefits including:
High Common-Mode Performance: The AD210 provides
2500 V rms (Continuous) and ± 3500 V peak (Continuous) common-
Precision, Wide Bandwidth
3-Port Isolation Amplifier
AD210
FUNCTIONAL BLOCK DIAGRAM
FB
16
–IN
17
+IN
19
ICOM
18
+VISS
14
–VISS
15
INPUT
OUTPUT
T1
DEMOD
FILTER
MOD
T2
1
VO
2
OCOM
3
+VOSS
4
–VOSS
T3
POWER
OUTPUT
POWER
SUPPLY
INPUT
POWER
SUPPLY
POWER
OSCILLATOR
30
29
PWR
PWR COM
AD210
mode voltage isolation between any two ports. Low input
capacitance of 5 pF results in a 120 dB CMR at a gain of 100,
and a low leakage current (2 µA rms max @ 240 V rms, 60 Hz).
High Accuracy: With maximum nonlinearity of ± 0.012% (B
Grade), gain drift of ± 25 ppm/°C max and input offset drift of
(± 10 ± 30/G) µV/°C, the AD210 assures signal integrity while
providing high level isolation.
Wide Bandwidth: The AD210’s full-power bandwidth of
20 kHz makes it useful for wideband signals. It is also effective
in applications like control loops, where limited bandwidth
could result in instability.
Small Size: The AD210 provides a complete isolation function
in a small DIP package just 1.00" × 2.10" × 0.350". The low
profile DIP package allows application in 0.5" card racks and
assemblies. The pinout is optimized to facilitate board layout
while maintaining isolation spacing between ports.
Three-Port Design: The AD210’s three-port design structure
allows each port (Input, Output, and Power) to remain independent. This three-port design permits the AD210 to be used
as an input or output isolator. It also provides additional system
protection should a fault occur in the power source.
Isolated Power: ± 15 V @ 5 mA is available at the input and
output sections of the isolator. This feature permits the AD210
to excite floating signal conditioners, front-end amplifiers and
remote transducers at the input as well as other circuitry at the
output.
Flexible Input: An uncommitted operational amplifier is provided at the input. This amplifier provides buffering and gain as
required and facilitates many alternative input functions as
required by the user.
REV. A
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
AD210–SPECIFICATIONS (typical @ +258C, and V = +15 V unless otherwise noted)
S
Model
AD210AN
AD210BN
OUTLINE DIMENSIONS
AD210JN
Dimensions shown in inches and (mm).
GAIN
Range
Error
vs. Temperature(0°C to +70°C)
(–25°C to +85°C)
vs. Supply Voltage
1
Nonlinearity
1 V/V – 100 V/V
± 2% max
+25 ppm/°C max
± 50 ppm/°C max
± 0.002%/V
± 0.025% max
*
± 1% max
*
*
*
± 0.012% max
*
*
*
*
*
*
INPUT VOLTAGE RATINGS
Linear Differential Range
Maximum Safe Differential Input
Max. CMV Input-to-Output
ac, 60 Hz, Continuous
dc, Continuous
Common-Mode Rejection
60 Hz, G = 100 V/V
RS ≤ 500 Ω Impedance Imbalance
Leakage Current Input-to-Output
@ 240 V rms, 60 Hz
± 10 V
± 15 V
*
2500 V rms
± 3500 V peak
*
*
120 dB
*
2 µA rms max
*
*
*
*
*
*
1500 V rms
± 2000 V peak
*
*
*
*
INPUT IMPEDANCE
Differential
Common Mode
l012 Ω
5 GΩi5 pF
*
*
*
*
INPUT BIAS CURRENT
Initial, @ +25°C
30 pA typ (400 pA max) *
vs. Temperature (0°C to +70°C)
10 nA max
*
(–25°C to +85°C) 30 nA max
*
*
*
*
INPUT DIFFERENCE CURRENT
Initial, @ +25°C
vs. Temperature(0°C to + 70°C)
(–25°C to +85°C)
5 pA typ (200 pA max)
2 nA max
10 nA max
*
*
*
*
*
*
INPUT NOISE
Voltage (l kHz)
(10 Hz to 10 kHz)
Current (1 kHz)
18 nV/√Hz
4 µV rms
0.01 pA/√Hz
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
FREQUENCY RESPONSE
Bandwidth (–3 dB)
*
G = 1 V/V
20 kHz
G = 100 V/V
15 kHz
Settling Time (± 10 mV, 20 V Step) *
G = 1 V/V
150 µs
G = 100 V/V
500 µs
Slew Rate (G = 1 V/V)
1 V/µs
OFFSET VOLTAGE (RTI)2
Initial, @ +25°C
vs. Temperature (0°C to +70°C)
(–25°C to +85°C)
± 15 ± 45/G) mV max
(± 10 ± 30/G) µV/°C
(± 10 ± 50/G) µV/°C
(± 5 ±15/G) mV max
*
*
*
*
*
RATED OUTPUT3
Voltage, 2 kΩ Load
Impedance
Ripple (Bandwidth = 100 kHz)
± 10 V min
1 Ω max
10 mV p-p max
*
*
*
*
*
*
ISOLATED POWER OUTPUTS 4
Voltage, No Load
Accuracy
Current
Regulation, No Load to Full Load
Ripple
± 15 V
± 10%
± 5 mA
See Text
See Text
*
*
*
*
*
*
*
*
*
*
POWER SUPPLY
Voltage, Rated Performance
Voltage, Operating
Current, Quiescent
Current, Full Load – Full Signal
+15 V dc ± 5%
+15 V dc ± 10%
50 mA
80 mA
*
*
*
*
*
*
*
*
TEMPERATURE RANGE
Rated Performance
Operating
Storage
–25°C to +85°C
–40°C to +85°C
–40°C to +85°C
*
*
*
*
*
*
PACKAGE DIMENSIONS
Inches
Millimeters
1.00 × 2.10 × 0.350
25.4 × 53.3 × 8.9
*
*
*
*
NOTES
*Specifications same as AD210AN.
1
Nonlinearity is specified as a % deviation from a best straight line..
2
RTI – Referred to Input.
3
A reduced signal swing is recommended when both ± VISS and ± VOSS supplies are fully
loaded, due to supply voltage reduction.
4
See text for detailed information.
_
Specifications subject to change without notice.
–2–
AC1059 MATING SOCKET
AD210 PIN DESIGNATIONS
Pin
Designation
Function
1
2
3
4
14
15
16
17
18
19
29
30
VO
OCOM
+VOSS
–VOSS
+VISS
–VISS
FB
–IN
ICOM
+IN
Pwr Com
Pwr
Output
Output Common
+Isolated Power @ Output
–Isolated Power @ Output
+Isolated Power @ Input
–Isolated Power @ Input
Input Feedback
–Input
Input Common
+Input
Power Common
Power Input
WARNING!
ESD SENSITIVE DEVICE
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can
discharge without detection. Although the AD210
features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to
high energy electrostatic discharges. Therefore,
proper ESD precautions are recommended to avoid
performance degradation or loss of functionality.
REV. A
AD210
RF
INSIDE THE AD210
The AD210 basic block diagram is illustrated in Figure 1.
A +15 V supply is connected to the power port, and
± 15 V isolated power is supplied to both the input and
output ports via a 50 kHz carrier frequency. The uncommitted input amplifier can be used to supply gain or buffering of input signals to the AD210. The fullwave
modulator translates the signal to the carrier frequency for
application to transformer T1. The synchronous demodulator in the output port reconstructs the input signal. A
20 kHz, three-pole filter is employed to minimize output
noise and ripple. Finally, an output buffer provides a low
impedance output capable of driving a 2 kΩ load.
FB
16
–IN
17
+IN
19
ICOM
18
+VISS
14
–VISS
15
INPUT
OUTPUT
T1
DEMOD
FILTER
MOD
T2
1
VO
2
OCOM
3
+VOSS
4
–VOSS
16
(
1
17
VSIG
AD210
2
18
14
+VISS
15
–VISS
30
30
29
PWR
PWR COM
+VOSS
3
–VOSS
4
29
+15V
Figure 3. Input Configuration for G > 1
Figure 4 shows how to accommodate current inputs or sum currents or voltages. This circuit configuration can also be used for
signals greater than ± 10 V. For example, a ± 100 V input span
can be handled with RF = 20 kΩ and RS1 = 200 kΩ.
IS
RF
16
OUTPUT
POWER
SUPPLY
INPUT
POWER
SUPPLY
POWER
OSCILLATOR
1
17
AD210
RS2
RS1
VS2
VS1
19
2
18
USING THE AD210
The AD210 is very simple to apply in a wide range of applications. Powered by a single +15 V power supply, the
AD210 will provide outstanding performance when used
as an input or output isolator, in single and multichannel
configurations.
14
+VISS
15
–VISS
Input Configurations: The basic unity gain configuration for signals up to ± 10 V is shown in Figure 2. Additional input amplifier variations are shown in the following
figures. For smaller signal levels Figure 3 shows how to
obtain gain while maintaining a very high input impedance.
16
1
17
VOUT
(±10V)
19
AD210
2
18
14
VOUT
+VISS
+VOSS
30
VOUT = –RF
VOUT
AD210
Figure 1. AD210 Block Diagram
VSIG
±10V
)
19
RG
T3
POWER
VOUT
R
= VSIG 1+ F
RG
VS1
V
( RS1 + RS2
S2
)
+ IS + ...
+VOSS
3
–VOSS
4
29
+15V
Figure 4. Summing or Current Input Configuration
Adjustments
When gain and offset adjustments are required, the actual circuit adjustment components will depend on the choice of input
configuration and whether the adjustments are to be made at
the isolator’s input or output. Adjustments on the output side
might be used when potentiometers on the input side would
represent a hazard due to the presence of high common-mode
voltage during adjustment. Offset adjustments are best done at
the input side, as it is better to null the offset ahead of the gain.
Figure 5 shows the input adjustment circuit for use when the input amplifier is configured in the noninverting mode. This offset
adjustment circuit injects a small voltage in series with the
GAIN
3
47.5kΩ
15
–VISS
–VOSS
30
16
4
5kΩ
29
1
17
19
+15V
Figure 2. Basic Unity Gain Configuration
VSIG
The high input impedance of the circuits in Figures 2 and
3 can be maintained in an inverting application. Since the
AD210 is a three-port isolator, either the input leads or
the output leads may be interchanged to create the signal
inversion.
AD210
RG
HI
LO
2
18
200Ω
14
+VISS
+VOSS
3
–VOSS
4
100kΩ
50kΩ
15
OFFSET
–VISS
30
29
+15V
Figure 5. Adjustments for Noninverting Input
REV. A
–3–
VOUT
AD210
low side of the signal source. This will not work if the source has
another current path to input common or if current flows in the
signal source LO lead. To minimize CMR degradation, keep the
resistor in series with the input LO below a few hundred ohms.
CHANNEL OUTPUTS
Figure 5 also shows the preferred gain adjustment circuit. The
circuit shows RF of 50 kΩ, and will work for gains of ten or
greater. The adjustment becomes less effective at lower gains
(its effect is halved at G = 2) so that the pot will have to be a
larger fraction of the total RF at low gain. At G = 1 (follower)
the gain cannot be adjusted downward without compromising
input impedance; it is better to adjust gain at the signal source
or after the output.
3
2
1
0.1"
GRID
POWER
Figure 6 shows the input adjustment circuit for use when the
input amplifier is configured in the inverting mode. The offset
adjustment nulls the voltage at the summing node. This is preferable to current injection because it is less affected by subsequent gain adjustment. Gain adjustment is made in the feedback
and will work for gains from 1 V/V to 100 V/V.
GAIN
47.5kΩ
5kΩ
1
17
RS
VOUT
19
2
18
+VISS
+VOSS
3
–VOSS
4
100kΩ
15
OFFSET
–VISS
30
RG RF
3
2
CHANNEL INPUTS
Synchronization: The AD210 is insensitive to the clock of an
adjacent unit, eliminating the need to synchronize the clocks.
However, in rare instances channel to channel pick-up may
occur if input signal wires are bundled together. If this happens,
shielded input cables are recommended.
50kΩ
14
1
Figure 8. PCB Layout for Multichannel Applications with
Gain
AD210
200Ω
VSIG
RG RF
RG RF
16
29
+15V
PERFORMANCE CHARACTERISTICS
Figure 6. Adjustments for Inverting Input
Figure 7 shows how offset adjustments can be made at the output, by offsetting the floating output port. In this circuit, ± 15 V
would be supplied by a separate source. The AD210’s output
amplifier is fixed at unity, therefore, output gain must be made
in a subsequent stage.
Common-Mode Rejection: Figure 9 shows the commonmode rejection of the AD210 versus frequency, gain and input
source resistance. For maximum common-mode rejection of
unwanted signals, keep the input source resistance low and carefully lay out the input, avoiding excessive stray capacitance at
the input terminals.
180
16
G=1
O =0
Ω
140
AD210
RL
50kΩ
200Ω
+VISS
+VOSS
–VISS
–VOSS
30
29
CMR – dB
2
18
15
RL
VOUT
19
14
G = 100
160
1
17
0.1µF
3
+15V
O =0
Ω
100
RL
O =1
0kΩ
100k
OFFSET
4
O =5
00Ω
RL
120
RL
80
O =1
0kΩ
–15V
60
+15V
Figure 7. Output-Side Offset Adjustment
40
10
PCB Layout for Multichannel Applications: The unique
pinout positioning minimizes board space constraints for multichannel applications. Figure 8 shows the recommended printed
circuit board layout for a noninverting input configuration with
gain.
20
50 60 100
200
500
1k
2k
5k
10k
FREQUENCY – Hz
Figure 9. Common-Mode Rejection vs. Frequency
–4–
REV. A
0
40
–20
φG = 1
GAIN – dB
20
–40
φG = 100
0
–60
–20
–80
–40
–100
–60
–120
–80
10
100
1k
10k
PHASE SHIFT – Degrees
60
ERROR – %
Phase Shift: Figure 10 illustrates the AD210’s low phase shift
and gain versus frequency. The AD210’s phase shift and wide
bandwidth performance make it well suited for applications like
power monitors and controls systems.
+0.04
+8
+0.03
+6
+0.02
+4
+0.01
+2
0
0
–0.01
–2
–0.02
–4
–0.03
–6
ERROR – mV
AD210
–8
–0.04
–10
–8
–6
–4
–2
0
+2
+4
+6
+8
+10
OUTPUT VOLTAGE SWING – Volts
Figure 12. Gain Nonlinearity Error vs. Output
0.01
100
–140
100k
90
0.009
80
0.008
70
0.007
60
0.006
50
0.005
40
0.004
30
0.003
20
0.002
10
0.001
ERROR – ppm of Signal Swing
Figure 10. Phase Shift and Gain vs. Frequency
Input Noise vs. Frequency: Voltage noise referred to the input
is dependent on gain and signal bandwidth. Figure 11 illustrates
the typical input noise in nV/√Hz of the AD210 for a frequency
range from 10 to 10 kHz.
60
NOISE – nV/√Hz
50
0.000
0
40
0
2
4
6
8
10
12
14
16
18
20
TOTAL SIGNAL SWING – Volts
Figure 13. Gain Nonlinearity vs. Output Swing
30
Gain vs. Temperature: Figure 14 illustrates the AD210’s
gain vs. temperature performance. The gain versus temperature
performance illustrated is for an AD210 configured as a unity
gain amplifier.
20
10
400
0
10
100
1k
10k
200
FREQUENCY – Hz
G=1
0
GAIN ERROR – ppm of Span
Figure 11. Input Noise vs. Frequency
Gain Nonlinearity vs. Output: Gain nonlinearity is defined as the
deviation of the output voltage from the best straight line, and is
specified as % peak-to-peak of output span. The AD210B provides
guaranteed maximum nonlinearity of ± 0.012% with an output span of
± 10 V. The AD210’s nonlinearity performance is shown in Figure 12.
Gain Nonlinearity vs. Output Swing: The gain nonlinearity
of the AD210 varies as a function of total signal swing. When
the output swing is less than 20 volts, the gain nonlinearity as a
fraction of signal swing improves. The shape of the nonlinearity
remains constant. Figure 13 shows the gain nonlinearity of the
AD210 as a function of total signal swing.
–200
–400
–600
–800
–1000
–1200
–1400
–1600
–25
0
+25
+50
+70
TEMPERATURE – °C
Figure 14. Gain vs. Temperature
REV. A
ERROR – % of Signal Swing
FREQUENCY – Hz
–5–
+85
AD210
Isolated Power: The AD210 provides isolated power at the
input and output ports. This power is useful for various signal
conditioning tasks. Both ports are rated at a nominal ± 15 V at
5 mA.
The load characteristics of the isolated power supplies are
shown in Figure 15. For example, when measuring the load
rejection of the input isolated supplies VISS, the load is placed
between +VISS and –VISS. The curves labeled VISS and VOSS are
the individual load rejection characteristics of the input and the
output supplies, respectively.
The isolated power supplies exhibit some ripple which varies as
a function of load. Figure 16a shows this relationship. The
AD210 has internal bypass capacitance to reduce the ripple to a
point where performance is not affected, even under full load.
Since the internal circuitry is more sensitive to noise on the
negative supplies, these supplies have been filtered more heavily.
Should a specific application require more bypassing on the isolated power supplies, there is no problem with adding external
capacitors. Figure 16b depicts supply ripple as a function of
external bypass capacitance under full load.
There is also some effect on either isolated supply when loading
the other supply. The curve labeled CROSSLOAD indicates the
sensitivity of either the input or output supplies as a function of
the load on the opposite supply.
RIPPLE – Peak-Peak Volts
1V
30
VOLTAGE
CROSSLOAD
100mV
+V
( +VISS
OSS )
10mV
ISS
( –V
–VOSS )
25
1mV
0.1µF
VOSS
VOSS
Figure 16b. Isolated Power Supply Ripple vs. Bypass
Capacitance (Volts p-p, 1 MHz Bandwidth, 5 mA Load)
VISS SIMULTANEOUS
20
5
100µF
10µF
CAPACITANCE
VISS
0
1µF
SIMULTANEOUS
APPLICATIONS EXAMPLES
10
CURRENT – mA
Figure 15. Isolated Power Supplies vs. Load
Lastly, the curves labeled VOSS simultaneous and VISS simultaneous indicate the load characteristics of the isolated power supplies when an equal load is placed on both supplies.
The AD210 provides short circuit protection for its isolated
power supplies. When either the input supplies or the output
supplies are shorted to input common or output common,
respectively, no damage will be incurred, even under continuous
application of the short. However, the AD210 may be damaged
if the input and output supplies are shorted simultaneously.
Noise Reduction in Data Acquisition Systems: Transformer
coupled isolation amplifiers must have a carrier to pass both ac
and dc signals through their signal transformers. Therefore,
some carrier ripple is inevitably passed through to the isolator
output. As the bandwidth of the isolator is increased more of the
carrier signal will be present at the output. In most cases, the
ripple at the AD210’s output will be insignificant when compared to the measured signal. However, in some applications,
particularly when a fast analog-to-digital converter is used following the isolator, it may be desirable to add filtering; otherwise ripple may cause inaccurate measurements. Figure 17
shows a circuit that will limit the isolator’s bandwidth, thereby
reducing the carrier ripple.
+VOSS
+VISS
16
100
R
RIPPLE – mV p-p
VSIG
+VOSS
75
AD542
R
1
17
–VOSS
19
AD210
0.001µF
VOUT
0.002µF
2
18
–VISS
50
–VOSS
14
+VISS
15
–VISS
+VOSS
3
–VOSS
4
R (kΩ) =
25
30
0
0
1
2
3
4
5
6
Under any circumstances, care should be taken to ensure that
the power supplies do not accidentally become shorted.
C
29
+15V
7
Figure 17. 2-Pole, Output Filter
LOAD – mA
Figure 16a. Isolated Supply Ripple vs. Load
(External 4.7 µ F Bypass)
( f 112.5
)
(kHz)
Self-Powered Current Source
The output circuit shown in Figure 18 can be used to create a
self-powered output current source using the AD210. The 2 kΩ
resistor converts the voltage output of the AD210 to an equiva–6–
REV. A
AD210
lent current VOUT/2 kΩ. This resistor directly affects the output
gain temperature coefficient, and must be of suitable stability for
the application. The external low power op amp, powered by
+VOSS and –VOSS, maintains its summing junction at output
common. All the current flowing through the 2 kΩ resistor flows
through the output Darlington pass devices. A Darlington configuration is used to minimize loss of output current to the base.
FDH333
16
+VOSS
2kΩ
VSIG
0-10V
1
17
2N3906
(2)
LF441
monitors the input terminal (cold-junction). Ambient temperature changes from 0°C to +40°C sensed by the AD590, are cancelled out at the cold junction. Total circuit gain equals 183;
100 and 1.83, from A1 and the AD210 respectively. Calibration
is performed by replacing the thermocouple junction with plain
thermocouple wire and a millivolt source set at 0.0000 V (0°C)
and adjusting RO for EOUT equal to 0.000 V. Set the millivolt
source to +0.02185 V (400°C) and adjust RG for VOUT equal to
+4.000 V. This application circuit will produce a nonlinearized
output of about +10 mV/°C for a 0°C to +400°C range.
–VISS
19
–VOSS
AD210
1000pF
13.7k 10k
THERMAL
CONTACT
2
18
RG
5k
AD590
16
14
+VISS
15
–VISS
30
+VOSS
3
–VOSS
4
ADJUST
TO 4mA
WITH 0V IN
500Ω
–VISS
14
+VISS
15
–VISS
30
+VISS
+15V
The AD7541 is a current output DAC and, as such, requires an
external output amplifier. The uncommitted input amplifier
internal to the AD210 may be used for this purpose. For best
results, its input offset voltage must be trimmed as shown.
+28V
CURRENT
LOOP
The output voltage of the AD210 will go from 0 V to –10 V for
digital inputs of 0 and full scale, respectively. However, since
the output port is truly isolated, VOUT and OCOM may be freely
interchanged to get 0 V to +10 V.
+VS
GAIN
2N2219
2kΩ
30
AD581
17
16
4
29
SPAN
ADJ
12-BIT
DIGITAL
INPUT
100Ω
1N4149
CURRENT
LOOP
4
15
AD7541
–VOSS
+VISS
+VISS
1kΩ
576Ω
–VISS
18
16
1
17
1
VOUT
0 - –10V
2
3
19
AD210
200Ω
2
18
RLOAD
50kΩ
+15V
HP5082-2811
OR EQUIVALENT
Figure 19. Isolated Voltage-to-Current Loop Converter
14
+VISS
+VOSS
3
–VOSS
4
100kΩ
Isolated Thermocouple Amplifier
15
OFFSET
The AD210 application shown in Figure 20 provides amplification, isolation and cold-junction compensation for a standard J
type thermocouple. The AD590 temperature sensor accurately
REV. A
4
The digital inputs of the AD7541 are TTL or CMOS compatible. Both the AD7541 and AD581 voltage reference are powered by the isolated power supply + VISS. ICOM should be tied to
input digital common to provide a digital ground reference for
the inputs.
2
3
–VOSS
The AD210, when combined with a digital-to-analog converter,
can be used to create a fully floating voltage output. Figure 21
shows one possible implementation.
–VS
+VOSS
3
This circuit provides a precision 0 V–10 V programmable reference with a ± 3500 V common-mode range.
AD308
+VISS
29
+VOSS
Figure 20. Isolated Thermocouple Amplifier
16
1
2
Precision Floating Programmable Reference
2N2907
15
1k 100k
10k
143Ω
3.0k
14
18
-20k-
Isolated V-to-I Converter
Illustrated in Figure 19, the AD210 is used to convert a 0 V to
+10 V input signal to an isolated 4–20 mA output current. The
AD210 isolates the 0 V to +10 V input signal and provides a
proportional voltage at the isolator’s output. The output circuit
converts the input voltage to a 4–20 mA output current, which
in turn is applied to the loop load RLOAD.
18
220pF
COLD
JUNCTION
Figure 18. Self-Powered Isolated Current Source
The low leakage diode is used to protect the base-emitter junction against reverse bias voltages. Using –VOSS as a current
return allows more than 10 V of compliance. Offset and gain
control may be done at the input of the AD210 or by varying
the 2 kΩ resistor and summing a small correction current
directly into the summing node. A nominal range of 1 mA–
5 mA is recommended since the current output cannot reach
zero due to reverse bias and leakage currents. If the AD210 is
powered from the input potential, this circuit provides a fully
isolated, wide bandwidth current output. This configuration is
limited to 5 mA output current.
AD210
19
AD210
RG
19
A1
52.3Ω
IOUT
RETURN
+15V
VSIG
1
17
"J"
29
17
VOUT
AD OP-07
IOUT
–VISS
30
29
+15V
Figure 21. Precision Floating Programmable Reference
–7–
AD210
200kΩ
8.25k
10T
AD210
16
RG 1kΩ
17
1
19
CHANNEL 1
2
18
25Ω
14
RO
50k
15
10T
RF
15.8k
16
RG 5k
17
50k
1kΩ
RO
1kΩ
AD590
CHANNEL 2
10T
+VISS
+VOSS
3
–VISS
–VOSS
4
30
29
AD210
+V
–V COM
1
19
2
18
–VISS
C1005–9–9/86
4-20mA
9.31k
50k
+VISS
AD580
100Ω
OFFSET
50k
14
+VISS
+VOSS
3
15
–VISS
–VOSS
4
10T
30
39k
29
TO A/D
AD210
16
+VISS
AD OP-07
AD7502
MULTIPLEXER
17
1
19
CHANNEL 3
EIN
1.0µF
0.47µF
50Ω
–VISS
50kΩ
+VISS
2
18
14
+VISS
+VOSS
3
15
–VISS
–VOSS
4
30
AD210
16
+10V
+VISS
17
A2
19
AD584
20k
CHANNEL 4
20k
–VISS
+VISS
20k
20k
1k
–VISS
1
2
18
14
+VISS
+VOSS
3
15
–VISS
–VOSS
4
1M
A1
CHANNEL
SELECT
29
30
29
COM
+15V
A1 A2 = AD547
DC POWER
SOURCE
Figure 22. Multichannel Data Acquisition Front-End
Illustrated in Figure 22 is a four-channel data acquisition frontend used to condition and isolate several common input signals
found in various process applications. In this application, each
AD210 will provide complete isolation from input to output as
well as channel to channel. By using an isolator per channel,
maximum protection and rejection of unwanted signals is
obtained. The three-port design allows the AD210 to be
configured as an input or output isolator. In this application the
isolators are configured as input devices with the power port
providing additional protection from possible power source
faults.
Channel 1: The AD210 is used to convert a 4–20 mA current
loop input signal into a 0 V–10 V input. The 25 Ω shunt resistor
converts the 4-20 mA current into a +100 mV to +500 mV signal.
The signal is offset by –100 mV via RO to produce a 0 mV to
+400 mV input. This signal is amplified by a gain of 25 to produce
the desired 0 V to +10 V output. With an open circuit, the AD210
will show –2.5 V at the output.
Channel 2: In this channel, the AD210 is used to condition and
isolate a current output temperature transducer, Model AD590. At
+25°C, the AD590 produces a nominal current of 298.2 µA. This
level of current will change at a rate of 1 µA/°C. At –17.8°C (0°F),
the AD590 current will be reduced by 42.8 µA to +255.4 µA. The
AD580 reference circuit provides an equal but opposite current,
resulting in a zero net current flow, producing a 0 V output from
the AD210. At +100°C (+212°F), the AD590 current output will
be 373.2 µA minus the 255.4 µA offsetting current from the
AD580 circuit to yield a +117.8 µA input current. This current is
converted to a voltage via RF and RG to produce an output of
+2.12 V. Channel 2 will produce an output of +10 mV/°F over a
0°F to +212°F span.
Channel 3: Channel 3 is a low level input channel configured with
a high gain amplifier used to condition millivolt signals. With the
AD210’s input set to unity and the input amplifier set for a gain of
1000, a ± 10 mV input will produce a ± 10 V at the AD210’s output.
Channel 4: Channel 4 illustrates one possible configuration for
conditioning a bridge circuit. The AD584 produces a +10 V
excitation voltage, while A1 inverts the voltage, producing negative
excitation. A2 provides a gain of 1000 V/V to amplify the low level
bridge signal. Additional gain can be obtained by reconfiguration
of the AD210’s input amplifier. ± VISS provides the complete power
for this circuit, eliminating the need for a separate isolated excitation source.
Each channel is individually addressed by the multiplexer’s channel select. Additional filtering or signal conditioning should follow
the multiplexer, prior to an analog-to-digital conversion stage.
–8–
REV. A
PRINTED IN U.S.A.
MULTICHANNEL DATA ACQUISITION FRONT-END