Page 1
120 kHz Bandwidth, Low Distortion,
OUT HI
TRIM
OUT LO
+15V
IN
–15V
IN
PWR RTN
FB
IN–
IN+
IN COM
+V
ISO
–V
ISO
1
3
MODULATOR
37
36
38
42
44
43
6
2
5
4
UNCOMMITTED
INPUT OP AMP
RR
OUTPUT
BUFFER
33kΩ
0.01µF
DEMODULATOR
LOW-PASS
FILTER
150kHz
POWER
ISOLATED
DC
SUPPLY
430kHz
POWER
OSCILLATOR
T1
T2
AD215
SIGNAL
a
FEATURES
Isolation Voltage Rating: 1,500 V rms
Wide Bandwidth: 120 kHz, Full Power (–3 dB)
Rapid Slew Rate: 6 V/ms
Fast Settling Time: 9 ms
Low Harmonic Distortion: –80 dB @ 1 kHz
Low Nonlinearity: 60.005%
Wide Output Range: 610 V, min (Buffered)
Built-in Isolated Power Supply: 615 V dc @ 610 mA
Performance Rated over –408C to +858C
APPLICATIONS INCLUDE
High Speed Data Acquisition Systems
Power Line and Transient Monitors
Multichannel Muxed Input Isolation
Waveform Recording Instrumentation
Power Supply Controls
Vibration Analysis
GENERAL DESCRIPTION
The AD215 is a high speed input isolation amplifier designed to
isolate and amplify wide bandwidth analog signals. The innovative circuit and transformer design of the AD215 ensures wideband dynamic characteristics while preserving key dc performance
specifications.
The AD215 provides complete galvanic isolation between the
input and output of the device including the user-available
front-end isolated power supplies. The functionally complete
design, powered by a ±15 V dc supply, eliminates the need for a
user supplied isolated dc/dc converter. This permits the designer
to minimize circuit overhead and reduce overall system design
complexity and component costs.
The design of the AD215 emphasizes maximum flexibility and
ease of use in a broad range of applications where fast analog
signals must be measured under high common-mode voltage
(CMV) conditions. The AD215 has a ± 10 V input/output
range, a specified gain range of 1 V/V to 10 V/V, a buffered output with offset trim and a user-available isolated front-end
power supply which produces ±15 V dc at ± 10 mA.
PRODUCT HIGHLIGHTS
High Speed Dynamic Characteristics: The AD215 features
a typical full-power bandwidth of 120 kHz (100 kHz min), rise
time of 3 µs and settling time of 9 µs. The high speed perfor-
mance of the AD215 allows for unsurpassed galvanic isolation
of virtually any wideband dynamic signal.
REV. 0
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.
Isolation Amplifier
AD215
FUNCTIONAL BLOCK DIAGRAM
Flexible Input and Buffered Output Stages: An uncommit-
ted op amp is provided on the input stage of the AD215 to
allow for input buffering or amplification and signal conditioning. The AD215 also features a buffered output stage to drive
low impedance loads and an output voltage trim for zeroing the
output offset where needed.
High Accuracy: The AD215 has a typical nonlinearity of
±0.005% (B grade) of full-scale range and the total harmonic
distortion is typically –80 dB at 1 kHz. The AD215 provides
designers with complete isolation of the desired signal without
loss of signal integrity or quality.
Excellent Common-Mode Performance: The AD215BY
(AD215AY) provides 1,500 V rms (750 V rms) common-mode
voltage protection from its input to output. Both grades feature
a low common-mode capacitance of 4.5 pF inclusive of the
dc/dc power isolation. This results in a typical common-mode
rejection specification of 105 dB and a low leakage current of
2.0 µA rms max (240 V rms, 60 Hz).
Isolated Power: An unregulated isolated power supply of
±15 V dc @ ±10 mA is available at the isolated input port of
the AD215. This permits the use of ancillary isolated front-end
amplifiers or signal conditioning components without the need
for a separate dc/dc supply. Even the excitation of transducers
can be accomplished in most applications.
Rated Performance over the –408C to +858C Temperature
Range: With an extended industrial temperature range rating,
the AD215 is an ideal isolation solution for use in many industrial environments.
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
Page 2
AD215–SPECIFICA TIONS
(Typical @ +258C, VS = 615 V dc, 2 kV output load, unless otherwise noted.)
AD215AY/BY
Parameter Conditions Min Typ Max Units
GAIN
1
Range
Error G = 1 V/V, No Load on V
ISO
1 10 V/V
±0.5 ±2%
vs. Temperature 0°C to +85°C +15 ppm/°C
–40°C to 0°C +50 ppm/°C
vs. Supply Voltage ±(14.5 V dc to 16.5 V dc) +100 ppm/V
vs. Isolated Supply Load
Nonlinearity
3
2
+20 ppm/mA
AD215BY Grade ±10 V Output Swing, G = 1 V/V ±0.005 ±0.015 %
±10 V Output Swing, G = 10 V/V ±0.01 %
AD215AY Grade ± 10 V Output Swing, G = 1 V/V ±0.01 ± 0.025 %
±10 V Output Swing, G = 10 V/V ±0.025 %
INPUT VOLTAGE RATINGS
Input Voltage Rating G = 1 V/V ±10 V
Maximum Safe Differential Range IN+ or IN–, to IN COM ±15 V
CMRR of Input Op Amp 100 dB
Isolation Voltage Rating
AD215BY Grade 100% Tested
AD215AY Grade 100% Tested
IMRR (Isolation Mode Rejection Ratio) R
4
Input to Output, AC, 60 Hz
≤ 100 Ω (IN+ & IN–), G = 1 V/V, 60 Hz 120 dB
S
R
≤ 100 Ω (IN+ & IN–), G = 1 V/V, 1 kHz 100 dB
S
R
≤ 100 Ω (IN+ & IN–), G = 1 V/V, 10 kHz 80 dB
S
R
≤ 1 kΩ (IN+ & IN–), G = 1 V/V, 60 Hz 105 dB
S
R
≤ 1 kΩ (IN+ & IN–), G = 1 V/V, 1 kHz 85 dB
S
R
≤ 1 kΩ (IN+ & IN–), G = 1 V/V, 10 kHz 65 dB
S
4
4
1500 V rms
750 V rms
Leakage Current, Input to Output 240 V rms, 60 Hz 2 µA rms
INPUT IMPEDANCE
Differential G = 1 V/V 16 MΩ
Common Mode 2i4.5 GΩipF
INPUT OFFSET VOLTAGE
Initial @ +25°C ±0.4 ±2.0 mV
vs. Temperature 0°C to +85°C ±2 µV/°C
–40°C to 0°C ±20 µV/°C
OUTPUT OFFSET VOLTAGE
Initial @ +25°C, Trimmable to Zero 0 –35 –80 mV
vs. Temperature 0°C to +85°C ±30 µV/°C
–40°C to 0°C ±80 µV/°C
vs. Supply Voltage ±350 µV/V
vs. Isolated Supply Load
2
–35 µV/mA
INPUT BIAS CURRENT
Initial @ +25°C 300 nA
vs. Temperature –40°C to +85°C ±400 nA
INPUT DIFFERENCE CURRENT
Initial @ +25°C ±3nA
vs. Temperature –40°C to +85°C ±40 nA
INPUT VOLTAGE NOISE
Input Voltage Noise Frequency > 10 Hz 20 nV/√Hz
DYNAMIC RESPONSE (2 kΩ Load)
Full Signal Bandwidth (–3 dB) G = 1 V/V, 20 V pk-pk Signal 100 120 kHz
Transport Delay
6
2.2 µs
Slew Rate ±10 V Output Swing 6 V/µs
Rise Time 10% to 90%, ±10 V Output Swing 3 µs
–2–
REV. 0
Page 3
AD215
AD215AY/BY
Parameter Conditions Min Typ Max Units
DYNAMIC RESPONSE (2 kΩ Load) Cont.
Settling Time to ±0.10%, ±10 V Output Swing 9 µs
Overshoot 1%
Harmonic Distortion Components @ 1 kHz –80 dB
@ 10 kHz –65 dB
Overload Recovery Time G = 1 V/V, ± 15 V Drive 5 µs
Output Overload Recovery Time G > 5 10 µs
RATED OUTPUT
Voltage Out HI to Out LO ±10 V
Current 2 kΩ Load ±5mA
Max Capacitive Load 500 pF
Output Resistance 1 Ω
Output Ripple and Noise
ISOLATED POWER OUTPUT
Voltage No Load ± 14.25 ±15 ±17.25 V
vs. Temperature 0°C to +85°C +20 mV/°C
Current at Rated Supply Voltage
Regulation No Load to Full Load –90 mV/V
Line Regulation 290 mV/V
Ripple 1 MHz Bandwidth, No Load
7
1 MHz Bandwidth 10 mV pk-pk
50 kHz Bandwidth 2.5 mV pk-pk
8
2, 9
–40°C to 0°C +25 mV/°C
±10 mA
2
50 mV rms
POWER SUPPLY
Supply Voltage Rated Performance ±14.5 ±15 ±16.5 V dc
Operating
10
±14.25 ±17 V dc
Current Operating (+15 V dc/–15 V dc Supplies) +40/–18 mA
TEMPERATURE RANGE
Rated Performance –40 +85 °C
Storage –40 +85 °C
NOTES
11
The gain range of the AD215 is specified from 1 to 10 V/V. The AD215 can also be used with gains of up to 100 V/V. With a gain of 100 V/V a 20% reduction in the
–3 dB bandwidth specification occurs and the nonlinearity degrades to ±0.02% typical.
12
When the isolated supply load exceeds ±1 mA, external filter capacitors are required in order to ensure that the gain, offset, and nonlinearity specifications are pre-
served and to maintain the isolated supply full load ripple below the specified 50 mV rms. A value of 6.8 µF is recommended.
13
Nonlinearity is specified as a percent (of full-scale range) deviation from a best straight line.
14
The isolation barrier (and rating) of every AD215 is 100% tested in production using a 5 second partial discharge test with a failure detection threshold of 150 pC. All
“B” grade devices are tested with a minimum voltage of 1,800 V rms. All “A” grade devices are tested with a minimum voltage of 850 V rms.
15
The AD215 should be allowed to warm up for approximately 10 minutes before any gain and/or offset adjustments are made.
16
Equivalent to a 0.8 degrees phase shift.
17
With the ±15 V dc power supply pins bypassed by 2.2 µF capacitors at the AD215 pins.
18
Caution: The AD215 design does not provide short circuit protection of its isolated power supply. A current limiting resistor may be placed in series with the isolated
power terminals and the load in order to protect the supply against inadvertent shorts.
19
With an input power supply voltage greater than or equal ±15 V dc, the AD215 may supply up to ± 15 mA from the isolated power supplies.
10
Voltages less than 14.25 V dc may cause the AD215 to cease operating properly. Voltages greater than ±17.5 V dc may damage the internal components of the
AD215 and consequently should not be used.
Specifications subject to change without notice.
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.
WARNING!
Although the AD215 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.
ESD SENSITIVE DEVICE
REV. 0
–3–
Page 4
AD215
IN–
IN+
IN COM
+V
–V
FB
ISO
ISO
4
3
1
2
6
5
UNCOMMITTED
INPUT OP AMP
ISOLATED
SIGNAL
DC
SUPPLY
MODULATOR
DEMODULATOR
T1
POWER
T2
Figure 1. Functional Block Diagram
LOW-PASS
FILTER
150kHz
430kHz
POWER
OSCILLATOR
AD215
R
R
OUTPUT
BUFFER
33kΩ
0.01µF
38
36
37
42
44
43
OUT HI
TRIM
OUT LO
+15V
IN
–15V
IN
PWR RTN
PIN CONFIGURATIONS
1
3
5
4
2
6
BOTTOM VIEW OF
FOOTPRINT
37
36 38
43
44
42
AD215 PIN DESIGNATIONS
Pin Designation Function
1 IN+ Noninverting Input
2 IN COM Input Common
3 IN– Inverting Input
4 FB Amplifier Feedback
5–V
6+V
OUT Isolated –15 V dc Power Supply
ISO
OUT Isolated +15 V dc Power Supply
ISO
36 TRIM Output Offset Trim Adjust
37 OUT LO Output Low
38 OUT HI Output High
42 +15 V
IN
+15 V dc Power
43 PWR RTN ±15 V dc Power Supply Common
44 –15 V
IN
–15 V dc Power
ORDERING GUIDE
Model Temperature Range V
CMV
Nonlinearity
*
AD215AY –40°C to +85°C 750 0.01%
AD215BY –40°C to +85°C 1500 0.005%
*Typical @ +25°C, G = 1 V/V.
INSIDE THE AD215
The AD215 is a fully self-contained analog signal and power
isolation solution. It employs a double-balanced amplitude
modulation technique to perform transformer coupling of signals ranging in frequency from true dc values to those having
frequencies of 120 kHz or less.
To generate the power supplies used for the isolated front-end
circuitry, an internal clock oscillator drives the primary winding
of the integral dc/dc power supply’s transformer, T2. The
resultant voltage developed across the secondary winding is
then rectified and filtered for use as the isolated power supply.
This built-in isolated dc/dc converter provides sufficient power
for both the internal isolated circuit elements of the AD215 as
well as any ancillary components supplied by the user. It saves
onboard space and component cost where additional amplification or signal conditioning is required.
After an input signal is amplified by the uncommitted op amp,
it is modulated at a carrier frequency of approximately 430 kHz
and applied across the primary winding of the signal isolation
transformer T1.
The resultant signal induced on the secondary winding of the
transformer is then demodulated and filtered using a low-pass
Bessel response filter set at a frequency of 150 kHz. The function of the filter reconstructs the original signal as it appears on
the input.
The signal transformer design and construction allow nonlinearity to be independent of both the specified temperature
and gain ranges.
After complete reconstruction, the signal is subjected to an offset trim stage and final output buffer. The trim circuit allows
the designer flexibility to adjust for any offset as desired.
–4–
REV. 0
Page 5
0.10
FREQUENCY – Hz
150
140
60
10 100k100
CMR – dB
1k 10k
130
120
110
100
90
80
70
RS ≤ 100Ω
RS ≤ 1kΩ
INPUT SIGNAL FREQUENCY – kHz
1
0
–12
0.1 10001.0
GAIN – dB
10 100
–1
–2
–3
–4
–5
–6
–7
–8
–9
–10
–11
G = 100
G = 10
G = 1
0.05
0
–0.05
–0.10
GAIN ERROR – %
–0.15
–0.20
–0.25
–40 100–20020406080
TEMPERATURE – °C
Performance Characteristics–AD215
Figure 2. Gain Error vs. Temperature
1mV
100
90
+1
0
–1
10
NONLINEARITY – mV
0%
–10 –8 –6 –4 –2 0 2 4 6 8 10
OUTPUT VOLTAGE – Volts
+0.004
–0.004
NONLINEARITY – %
Figure 3. Gain Nonlinearity vs. Output Voltage (G = 1 V/V)
3
2
1
0
DELAY – µs
TRANSPORT
0
Figure 4. Typical Common-Mode Rejection vs. Frequency
Figure 5. Normalized Gain as a Function of Signal
Frequency
G = 100
G =10
G = 1
REV. 0
45
90
130
PHASE SHIFT – Degrees
10 20 30 40 50 60 70 80 90 100 110 120
FREQUENCY – kHz
Figure 6. Phase Shift and Transport Delay vs. Frequency
–5–
G = 1
G =10
G = 100
Page 6
AD215–Performance Characteristics
100
90
100mV
5V
10
0%
5µs
OVERSHOOT
Figure 7a. Overshoot to a Full-Scale Step Input
(G = 1 V/V)
100
90
5V
OUTPUT
INPUT
(+10V STEP)
INPUT
(–10V STEP)
60
56
52
48
44
40
36
32
28
24
RIPPLE – mV p-p
20
ISO
V
16
12
8
4
0
010123456789
Figure 9.±V
16.2
16.0
15.8
0.33µF BYPASS CAPS
1.0µF BYPASS CAPS
3.3µF BYPASS CAPS
10µF BYPASS CAPS
V
LOAD – mA
ISO
Supply Ripple vs. Load
ISO
VS = ±15V dc
100mV
10
0%
5µs
UNDERSHOOT
OUTPUT
Figure 7b. Undershoot to a Full-Scale Input
(G = 1 V/V)
5V
100
90
10
0%
±10V, 15kHz STEP OUTPUT RESPONSE (G=1)
10µs
Figure 8. Output Response to Full-Scale Step Input
(G = 1 V/V)
15.6
– ±V
ISO
V
15.4
15.2
15.0
14.8
Figure 10.±V
NOTE:
THE GAIN AND
OFFSET ERRORS
WILL INCREASE
WHEN THE
ISOLATED
POWER SUPPLY
LOAD EXCEEDS
±10mA
V
LOAD – ±mA
ISO
Supply Voltage vs. Load
ISO
15510
–6–
REV. 0
Page 7
AD215
R
IN
= 2kΩ
V
SIGNAL
IN+
IN–
FB
IN COM
OUT HI
OUT LO
PWR
RTN
COM
TRIM
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
1
3
4
2
38
36
37
43
AD215
C
F
47pF
R
F
R
G
POWERING THE AD215
The AD215 is powered by a bipolar ±15 V dc power supply
connected as shown in Figure 11. External bypass capacitors
should be provided in bused applications. Note that a small
signal-related current (50 mA/V
) will flow out of the OUT
OUT
LO pin (Pin 37). Therefore, the OUT LO terminals should be
bused together and referenced at a single “Analog Star Ground”
to the ±15 V dc supply common as illustrated Figure 11.
AD215
N
OUT LO
37
42
43
44
NTH CHANNEL 1ST CHANNEL
N
AD215
37
42
43
44
1
ANALOG STAR GROUND
OUT LO
1
+V
IN
PWR RTN
–V
IN
SIG COM
+15V dc
2.2µF
COM
2.2µF
–15V dc
Figure 11. Typical Power Supply Connections
Power Supply Voltage Considerations
The rated performance of the AD215 remains unaffected for
power supply voltages in the ±14.5 V dc to ±16.5 V dc range.
Voltages below ±14.25 V dc may cause the AD215 to cease operating properly.
Note: Power supply voltages greater than ±17.5 V dc may damage
the internal components and consequently should not be used.
USING THE AD215
Unity Gain Input Configuration
The basic unity gain configuration for input signals of up to
±10 V is shown in Figure 12.
R
= 2kΩ
V
SIGNAL
IN
1
3
4
2
IN+
IN–
FB
IN COM
AD215
OUTPUT FILTER,
BUFFER AND
TRIM CIRCUITRY
TRIM
38
37
36
43
OUT HI
OUT LO
PWR
RTN
COM
Noninverting Configuration for Gain Greater Than Unity
Figure 13 shows how to achieve a gain greater than one while
continuing to preserve a very high input impedance. A recommended PC board layout for multichannel applications is shown
in Figure 20b.
Figure 13. Noninverting Input Configuration for
Gain > 1 V/V
In this circuit, the gain equation is as follows:
= (1 + RF/RG) × V
V
O
SIG
where:
= Output Voltage (V)
V
O
V
= Input Signal Voltage (V)
SIG
R
= Feedback Resistor Value (Ω)
F
R
= Gain Resistor Value (Ω)
G
The values for resistors R
and RG are subject to the following
F
constraints:
• The total impedance of the gain network should be less than
10 kΩ.
• The current drawn in R
is less than 1 mA at ±10 V. Note that
F
for each mA drawn by the feedback resistor, the isolated
power supply drive capability decreases by 1 mA.
• Amplifier gain is set by the feedback (R
(R
).
G
It is recommended that R
is bypassed with a 47 pF capacitor as
F
) and gain resistor
F
shown.
Note: The 2 kΩ input resistor (R
) in series with the input
IN
signal source and the IN+ terminal in Figures 12 and 13 is recommended to limit the current at the input terminals of the to
5.0 mA when the AD215 is not powered.
REV. 0
Figure 12. Basic Unity Gain
–7–
Page 8
AD215
Compensating the Uncommitted Input Op Amp
The open-loop gain and phase versus frequency for the uncommitted input op amp are given in Figure 14. These curves can
be used to determine appropriate values for the feedback resistor (R
) and compensation capacitor (CF) to ensure frequency
F
stability when reactive or nonlinear components are used.
25
20
15
10
5
0
–5
–10
–15
AVERAGE VOLTAGE GAIN – dB
–20
–25
100k 100M1M
FREQUENCY – Hz
PHASE
GAIN
10M
80
100
120
140
160
180
200
220
Ø, EXCESS PHASE – Degrees
240
260
280
Figure 14. Open-Loop Gain and Frequency Response
Inverting, Summing or Current Input Configuration
Figure 14 shows how the AD215 can measure currents or sum
currents or voltages.
FB
4
C
R
R
R
I
S
S2
V
V
S2
F
F
47pF
IN–
3
IN+
S1
S1
1
2
IN COM
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
AD215
TRIM
38
37
36
43
OUT HI
OUT LO
PWR
RTN
COM
Figure 15. Noninverting Summing/Current Configuration
For this circuit, the output voltage equation is:
= –RF × (IS + VS1/RS1 + VS2/RS2 + . . .)
V
O
where:
V = Output Voltage (V)
V
= Input Voltage Signal 1 (V)
S1
V
= Input Voltage Signal 2 (V)
S2
I
= Input Current Source (A)
S
R
= Feedback Resistor (Ω) (10 kΩ, typ)
F
R
= Input Signal 1 Source Resistance (Ω)
S1
R
= Input Signal 2 Source Resistance (Ω)
S2
The circuit of Figure 15 can also be used when the input signal
is larger than the ±10 V input range of the isolator. For example,
in Figure 15, if only V
with the solid lines, the input voltage span of V
modate up to ±50 V when R
, RS1 and RF were connected as shown
S1
= 10 kΩ and RS1 = 50 kΩ.
F
could accom-
S1
GAIN AND OFFSET ADJUSTMENTS
General Comments
The AD215 features an output stage TRIM pin useful for zeroing the output offset voltage through use of user supplied circuitry.
When gain and offset adjustments are required, the actual compensation circuit ultimately used depends on the following:
• The input configuration mode of the isolation amplifier (noninverting or inverting).
• The placement of any adjusting potentiometer (on the
isolator’s input or output side).
As a general rule:
• Gain adjustments should be accomplished at the gain-setting
resistor network at the isolator’s input.
• To ensure stability in the gain adjustment, potentiometers
should be located as close as possible to the isolator’s input
and its impedance should be kept low. Adjustment ranges
should also be kept to a minimum since their resolution and
stability is dependent upon the actual potentiometers used.
• Output adjustments may be necessary where adjusting potentiometers placed near the input would present a hazard to the
user due to the presence of high common-mode voltages during the adjustment procedure.
• It is recommended that input offset adjustments are made
prior to gain adjustments.
• The AD215 should be allowed to warm up for approximately
10 minutes before gain or offset adjustments are made.
Input Gain Adjustments for Noninverting Mode
Figure 16 shows a suggested noninverting gain adjustment circuit. Note that the gain adjustment potentiometer R
is incorpo-
P
rated into the gain-setting resistor network.
R
= 2kΩ
V
SIGNAL
IN
R
P
0.47pF
R
C
R
R
G
IN+
1
IN–
3
C
F
FB
4
F
2
IN COM
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
AD215
TRIM
38
37
36
43
OUT HI
OUT LO
PWR
RTN
COM
Figure 16. Gain Adjustment for Noninverting Configuration
For a ±1% trim range:
× R
R
G
(RP≈1kΩ), RC≈ 0.02×
RG+ R
F
F
–8–
REV. 0
Page 9
AD215
Input Gain Adjustments for the Inverting Mode
Figure 17 shows a suggested inverting gain adjustment circuit.
In this circuit, gain adjustment is made using a potentiometer
(R
) in the feedback loop. The adjustments are effective for all
P
gains in the 1 to 10 V/V range.
R
R
V
SIGNAL
R
IN
R
1kΩ
F
C
47pF
F
FB
4
C
F
IN–
3
1
2
IN+
IN COM
AD215
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
TRIM
38
37
36
43
OUT HI
OUT LO
PWR
RTN
COM
Figure 17. Gain Adjustment for Inverting Configuration
For an approximate ±1% gain trim range,
R
RX=
IN×RF
RIN+R
F
and select
= 0.02 × R
R
C
IN
while
R
< 10 kΩ
F
CF = 47 pF
Note: R
and RIN should have matched temperature coefficient
F
drift characteristics.
Output Offset Adjustments
Figure 18 illustrates one method of adjusting the output offset
voltage. Since the AD215 exhibits a nominal output offset of
–35 mV, the circuit shown was chosen to yield an offset correction of 0 mV to +73 mV. This results in a total output offset
range of approximately –35 mV to +38 mV.
IN–
3
1
4
2
IN+
FB
IN COM
LOW-PASS
AD215
FILTER,
(150kΩ)
OUTPUT
BUFFER
33kΩ
0.01µF
+15V
PWR RTN
–15V
TRIM
IN
IN
38
36
OUT LO
37
42
43
44
OUT HI
R
T
1MΩ
2.2µF
2.2µF
R
P2
10kΩ
R
S
100kΩ
+15V dc
COM
–15V dc
Figure 18. Output Offset Adjustment Circuit
Output Gain Adjustments
Since the output amplifier stage of the AD215 is fixed at unity
gain, any adjustments can be made only in a subsequent stage.
USING ISOLATED POWER
Each AD215 provides an unregulated, isolated bipolar power
source of ±15 V dc @ ±10 mA, referred to the input common.
This source may be used to power various ancillary components
such as signal conditioning and/or adjustment circuitry, references, op amps or remote transducers. Figure 19 shows typical
connections.
AND
430kHz
POWER
OSCILLATOR
AD215
TRIM
+V
PWR
RTN
–V
OUT HI
38
OUT LO
37
36
S
42
43
S
44
2.2µF
2.2µF
+15V dc
COM
–15V dc
LOAD
1.5kΩ
1.5kΩ
6.8µF
6.8µF
IN–
3
IN+
1
FB
4
IN COM
2
+V
ISO
6
C1
C2
ISOLATED
SUPPLY
–V
ISO
5
DC
OUTPUT
FILTER,
BUFFER
TRIM
CIRCUITRY
Figure 19. Using the Isolated Power Supplies
PCB LAYOUT FOR MULTICHANNEL APPLICATIONS
The pin out of the AD215 has been designed to easily facilitate
multichannel applications. Figure 20a shows a recommended
circuit board layout for a unity gain configuration.
PWR
RTN
+15V dc
2.2µF
38
36
37
36
37
36
37
36
37
38
38
38
42 44
42 44
42 44
42 44
2.2µF
–15V dc
2.2µF
43
43
43
43
2.2µF
SUPPLY BYPASS
CAPACITORS FOR
EVERY FOUR
AD215s
OUT HI
0
TRIM
0
OUT HI
1
TRIM
1
OUT HI
2
TRIM
OUT HI
TRIM
ANALOG
2
STAR
GROUND
3
3
Figure 20a. PCB Layout for Unity Gain
CAUTION
The AD215 design does not provide short-circuit protection of
its isolated power supply. A current limiting resistor should be
placed in series with the supply terminals and the load in order
to protect against inadvertent shorts.
REV. 0
–9–
Page 10
AD215
When gain setting resistors are used, 0.325" channel centers can
still be achieved as shown in Figure 20b.
R
IN
IN COM
+V
ISO
–V
I
SO
IN
IN COM
+V
ISO
–V
SO
I
C1, C2 ARE V
, RG ARE FEEDBACK, GAIN RESISTORS.
R
F
IS A FEEDBACK BYPASS CAPACITOR.
C
F
FILTER CAPACITORS.
ISO
F
R
F
C
F
R
G
C2
C
R
G
C2
C1
F
C1
2
1
2
1
6
4
5
3
6
4
5
3
Figure 20b. PCB Layout for Gain Greater than Unity
APPLICATIONS EXAMPLES
Motor Control
Figure 21 shows an AD215 used in a dc motor control application. Its excellent phase characteristics and wide bandwidth are
ideal for this type of application.
MOTOR
COMMAND
±10 VOLTS
COM
AD215
ISOLATED
4
3
1
G = 1
MOTOR
COMMAND
38
V
±10V
C
37
2
OUT LO
MOTOR
CONTROL
UNIT
ENCODER FEEDBACK
I
MOTOR
MOTOR
SHAFT
TACHOMETER
θ
OPTICAL
RESOLVER
OR
ENCODER
Figure 21. Motor Control Application
Multichannel Data Acquisition
The current drive capabilities of the AD215’s bipolar ±15 V dc
isolated power supply is more than adequate to meet the modest
±800 µA supply current requirements for the AD7502 multiplexer. Digital isolation techniques should be employed to isolate the Enable (EN), A0 and A1 logic control signals.
AC Transducer Applications
In applications such as vibration analysis, where the user must
acquire and process the spectral content of a sensor’s signal
rather than its “dc” level, the wideband characteristics of the
AD215 prove most useful. Key specifications for ac transducer
applications include bandwidth, slew rate and harmonic distortion. Since the transducer may be mechanically bonded or
welded to the object under test, isolation is typically required to
eliminate ground loops as well as protect the electronics used in
the data acquisition system. Figure 23 shows an isolated strain
gage circuit employing the AD215 and a high speed operational
amplifier (AD744).
To alleviate the need for an instrumentation amplifier, the
bridge is powered by a bipolar excitation source. Under this approach the common-mode voltage is ±V
only a few millivolts, rather than the V
which is typically
SPAN
4 2 that would be
EXC
achieved with a unipolar excitation source and Wheatstone
bridge configuration.
Using two strain gages with a gage factor of 3 mV/V and a
±1.2 V excitation signal, a ±6.6 mV output signal will result. A
gain setting of 454 will scale this low level signal to ±3 V, which
can then be digitized by a high speed, 100 kHz sampling ADC
such as the AD7870.
The low voltage excitation is used to permit the front-end circuitry to be powered from the isolated power supplies of the
AD215, which can supply up to ±10 mA of isolated power at
±15 V. The bridge draws only 3.5 mA, leaving sufficient current to power the micropower dual BiFET (400 µA quiescent
current) and the high speed AD744 BiFET amplifier (4 mA
quiescent current).
EN A1
A0
AD7502
(–15V)
(+15V)
DTL/TTL TO CMOS LEVEL
GND
DECODER/DRIVER
S1 – S4
TRANSLATOR
S5 – S8
6.8µF
6.8µF
FB
4
IN–
3
IN+
1
IN COM
2
+V
6
COM
2
–V
5
ISO
ISO
AD215
G = 1
38
37
42
44
43
OUT HI
OUT LO
+15V
–15V
PWR
RTN
Figure 22. Multichannel Data Acquisition Application
–10–
REV. 0
Page 11
AD215
1/2
220Ω
220Ω
350Ω
+
350Ω
–
+V
ISO
Q1
2N3904
+1.2V
ε
ε
–1.2V
Q2
2N3906
–V
ISO
1kΩ
–V
ISO
1MΩ
2MΩ
2.2pF
453kΩ
AD744
FB
4
IN–
3
IN+
1
MOD
DEMOD
OUTPUT
FILTER
AND
BUFFER
AD215
+V
ISO
6
6.8µF
C1
C2
6.8µF
COM
2
–V
ISO
5
ISOLATED
DC
SUPPLY
430kHz
POWER
OSC
38
37
36
42
44
43
OUT HI
OUT LO
TRIM
+15V
–15V
PWR
RTN
+V
ISO
1/2
AD648
+V
ISO
6.8kΩ
9.76kΩ500Ω
AD589
10kΩ
AD648
–V
ISO
Figure 23. Strain Gage Signal Conditioning Application
REV. 0
–11–
Page 12
AD215
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
AD215 SIP PACKAGE
2.480 (63.0) MAX
0.020 (0.5)
0.015 (0.4)
0.16 (4.1)
0.250
0.05 (1.3)
0.325
(6.4)
1
5
(8.3)
MAX
3
62
4
0.022 (0.56)
NOTE: PINS MEASURE 0.022 (0.56) x 0.010 (0.25) PRIOR TO TINNING.
TINNING MAY ADD UP TO 3 mils (0.003") TO THESE DIMENSIONS.
BOTTOM VIEW OF
0.712 (18.2)
2.15 (54.6)
1.50 (38.1)
FOOTPRINT
C
L
0.12 (3.0) TYP
0.094 (2.4)
0.712 (18.2)
0.1 (2.5)
36 38
0.325 (8.3)
MAX
0.010
(0.25)
0.1
(2.5)
0.840
(21.4)
MAX
0.165 (4.2)
0.135 (3.4)
C2134–20–4/96
0.815
(20.7)
30° TYP
0.16 (4.1)
0.2
(5.1)
0.1 (2.5)
0.11 (2.8)
43
37
42 44
0.11 (2.8)
–12–
PRINTED IN U.S.A.
REV. 0
Loading...