AD AD215 120 khz bandwidth, low distortion, isolation amplifier Datasheet

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
120 kHz Bandwidth, Low Distortion,
Isolation Amplifier
AD215
FUNCTIONAL BLOCK DIAGRAM
FB 4
AD215
UNCOMMITTED
INPUT OP AMP
SIGNAL
R
IN– 3
IN+ 1
MODULATOR
IN COM 2
DEMODULATOR
R
38 OUT HI
LOW-PASS
FILTER
150kHz
OUTPUT
BUFFER
T1
36 TRIM
33kΩ
0.01µF
37 OUT LO
POWER
APPLICATIONS INCLUDE
High Speed Data Acquisition Systems
Power Line and Transient Monitors
Multichannel Muxed Input Isolation
Waveform Recording Instrumentation
Power Supply Controls
Vibration Analysis
+VISO 6
–VISO 5
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 performance of the AD215 allows for unsurpassed galvanic isolation
of virtually any wideband dynamic signal.
430kHz
POWER
OSCILLATOR
ISOLATED
DC
SUPPLY
T2
42 +15VIN
44 –15VIN
43 PWR RTN
Flexible Input and Buffered Output Stages: An uncommitted 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.
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.
© 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
AD215–SPECIFICATIONS (Typical @ +258C, V = 615 V dc, 2 kV output load, unless otherwise noted.)
S
Parameter
GAIN
Range1
Error
vs. Temperature
vs. Supply Voltage
vs. Isolated Supply Load2
Nonlinearity3
AD215BY Grade
AD215AY Grade
INPUT VOLTAGE RATINGS
Input Voltage Rating
Maximum Safe Differential Range
CMRR of Input Op Amp
Isolation Voltage Rating4
AD215BY Grade
AD215AY Grade
IMRR (Isolation Mode Rejection Ratio)
Leakage Current, Input to Output
INPUT IMPEDANCE
Differential
Common Mode
INPUT OFFSET VOLTAGE
Initial
vs. Temperature
OUTPUT OFFSET VOLTAGE
Initial
vs. Temperature
Conditions
Min
AD215AY/BY
Typ
Max
1
G = 1 V/V, No Load on VISO
0°C to +85°C
–40°C to 0°C
± (14.5 V dc to 16.5 V dc)
± 0.5
+15
+50
+100
+20
± 10 V Output Swing, G = 1 V/V
± 10 V Output Swing, G = 10 V/V
± 10 V Output Swing, G = 1 V/V
± 10 V Output Swing, G = 10 V/V
± 0.005
± 0.01
± 0.01
± 0.025
G = 1 V/V
IN+ or IN–, to IN COM
Input to Output, AC, 60 Hz
100% Tested4
100% Tested4
RS ≤ 100 Ω (IN+ & IN–), G = 1 V/V, 60 Hz
RS ≤ 100 Ω (IN+ & IN–), G = 1 V/V, 1 kHz
RS ≤ 100 Ω (IN+ & IN–), G = 1 V/V, 10 kHz
RS ≤ 1 kΩ (IN+ & IN–), G = 1 V/V, 60 Hz
RS ≤ 1 kΩ (IN+ & IN–), G = 1 V/V, 1 kHz
RS ≤ 1 kΩ (IN+ & IN–), G = 1 V/V, 10 kHz
240 V rms, 60 Hz
± 10
Units
10
±2
V/V
%
ppm/°C
ppm/°C
ppm/V
ppm/mA
± 0.015
%
%
%
%
± 0.025
V
V
dB
± 15
100
1500
750
120
100
80
105
85
65
2
V rms
V rms
dB
dB
dB
dB
dB
dB
µA rms
G = 1 V/V
16
2i4.5
@ +25°C
0°C to +85°C
–40°C to 0°C
± 0.4
±2
± 20
± 2.0
mV
µV/°C
µV/°C
–35
± 30
± 80
± 350
–35
–80
mV
µV/°C
µV/°C
µV/V
µV/mA
@ +25°C, Trimmable to Zero
0°C to +85°C
–40°C to 0°C
0
vs. Supply Voltage
vs. Isolated Supply Load2
MΩ
GΩipF
INPUT BIAS CURRENT
Initial
vs. Temperature
@ +25°C
–40°C to +85°C
300
± 400
nA
nA
INPUT DIFFERENCE CURRENT
Initial
vs. Temperature
@ +25°C
–40°C to +85°C
±3
± 40
nA
nA
INPUT VOLTAGE NOISE
Input Voltage Noise
Frequency > 10 Hz
20
nV/√Hz
120
2.2
6
3
kHz
µs
V/µs
µs
DYNAMIC RESPONSE (2 kΩ Load)
Full Signal Bandwidth (–3 dB)
Transport Delay6
Slew Rate
Rise Time
G = 1 V/V, 20 V pk-pk Signal
± 10 V Output Swing
10% to 90%, ± 10 V Output Swing
–2–
100
REV. 0
AD215
Parameter
DYNAMIC RESPONSE (2 kΩ Load) Cont.
Settling Time
Overshoot
Harmonic Distortion Components
Overload Recovery Time
Output Overload Recovery Time
RATED OUTPUT
Voltage
Current
Max Capacitive Load
Output Resistance
Output Ripple and Noise7
ISOLATED POWER OUTPUT8
Voltage
vs. Temperature
Current at Rated Supply Voltage2, 9
Regulation
Line Regulation
Ripple
POWER SUPPLY
Supply Voltage
Current
Conditions
Min
to ± 0.10%, ± 10 V Output Swing
@ 1 kHz
@ 10 kHz
G = 1 V/V, ± 15 V Drive
G>5
Out HI to Out LO
2 kΩ Load
AD215AY/BY
Typ
Max
9
1
–80
–65
5
10
µs
%
dB
dB
µs
µs
500
1
10
2.5
V
mA
pF
Ω
mV pk-pk
mV pk-pk
± 10
±5
1 MHz Bandwidth
50 kHz Bandwidth
Units
1 MHz Bandwidth, No Load2
± 14.25 ± 15
+20
+25
± 10
–90
290
50
Rated Performance
Operating10
Operating (+15 V dc/–15 V dc Supplies)
± 14.5 ± 15
± 16.5
± 14.25
± 17
+40/–18
V dc
V dc
mA
–40
–40
°C
°C
No Load
0°C to +85°C
–40°C to 0°C
No Load to Full Load
TEMPERATURE RANGE
Rated Performance
Storage
± 17.25
+85
+85
V
mV/°C
mV/°C
mA
mV/V
mV/V
mV rms
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 preserved 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.
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.
REV. 0
–3–
WARNING!
ESD SENSITIVE DEVICE
AD215
FB 4
AD215
UNCOMMITTED
INPUT OP AMP
IN–
IN+ 1
IN COM
SIGNAL
MODULATOR
R
R
3
DEMODULATOR
LOW-PASS
FILTER
150kHz
2
38
OUT HI
36
TRIM
37
OUT LO
42
+15VIN
44
–15VIN
43
PWR RTN
OUTPUT
BUFFER
T1
33kΩ
0.01µF
POWER
+VISO 6
–VISO 5
430kHz
POWER
OSCILLATOR
ISOLATED
DC
SUPPLY
T2
Figure 1. Functional Block Diagram
INSIDE THE AD215
PIN CONFIGURATIONS
1
3
2
5
4
BOTTOM VIEW OF
FOOTPRINT
6
37
43
36 38
42 44
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.
AD215 PIN DESIGNATIONS
Pin
Designation
Function
1
2
3
4
5
6
36
37
38
42
43
44
IN+
IN COM
IN–
FB
–VISO OUT
+VISO OUT
TRIM
OUT LO
OUT HI
+15 VIN
PWR RTN
–15 VIN
Noninverting Input
Input Common
Inverting Input
Amplifier Feedback
Isolated –15 V dc Power Supply
Isolated +15 V dc Power Supply
Output Offset Trim Adjust
Output Low
Output High
+15 V dc Power
± 15 V dc Power Supply Common
–15 V dc Power
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.
ORDERING GUIDE
Model
Temperature Range
VCMV
Nonlinearity*
AD215AY
AD215BY
–40°C to +85°C
–40°C to +85°C
750
1500
0.01%
0.005%
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.
*Typical @ +25°C, G = 1 V/V.
–4–
REV. 0
Performance Characteristics–AD215
150
0.10
140
0.05
130
RS ≤ 100Ω
120
CMR – dB
GAIN ERROR – %
0
–0.05
–0.10
110
100
90
RS ≤ 1kΩ
–0.15
80
–0.20
70
–0.25
–40
–20
0
20
40
60
TEMPERATURE – °C
80
60
10
100
100
1k
FREQUENCY – Hz
10k
100k
Figure 4. Typical Common-Mode Rejection vs. Frequency
Figure 2. Gain Error vs. Temperature
1
0
–1
–2
–3
0
–0.004
–1
10
GAIN – dB
+0.004
+1
NONLINEARITY – %
NONLINEARITY – mV
1mV
100
90
–4
–5
–6
–7
G=1
–8
–9
0%
G = 10
–10
–11
–10 –8
–6 –4 –2 0
2
4
6
OUTPUT VOLTAGE – Volts
8
10
1.0
10
100
INPUT SIGNAL FREQUENCY – kHz
G = 100
G =10
G=1
3
2
1
0
PHASE SHIFT – Degrees
0
45
90
G=1
G =10
130
G = 100
10
20
30
40
50 60 70 80 90 100 110 120
FREQUENCY – kHz
Figure 6. Phase Shift and Transport Delay vs. Frequency
REV. 0
1000
Figure 5. Normalized Gain as a Function of Signal
Frequency
Figure 3. Gain Nonlinearity vs. Output Voltage (G = 1 V/V)
TRANSPORT
DELAY – µs
G = 100
–12
0.1
–5–
AD215–Performance Characteristics
60
56
52
100
OUTPUT
90
VISO RIPPLE – mV p-p
INPUT
(+10V STEP)
5V
0.33µF BYPASS CAPS
48
100mV
10
0%
5µs
44
40
36
32
1.0µF BYPASS CAPS
28
24
20
3.3µF BYPASS CAPS
16
12
OVERSHOOT
8
10µF BYPASS CAPS
4
0
0
Figure 7a. Overshoot to a Full-Scale Step Input
(G = 1 V/V)
1
2
3
4
5
6
VISO LOAD – mA
7
8
9
10
Figure 9. ± VISO Supply Ripple vs. Load
16.2
100
16.0
90
5V
INPUT
(–10V STEP)
VISO – ±V
100mV
OUTPUT
10
VS = ±15V dc
15.8
0%
5µs
15.6
15.4
NOTE:
THE GAIN AND
OFFSET ERRORS
WILL INCREASE
WHEN THE
ISOLATED
POWER SUPPLY
LOAD EXCEEDS
±10mA
15.2
UNDERSHOOT
15.0
14.8
Figure 7b. Undershoot to a Full-Scale Input
(G = 1 V/V)
5
10
15
VISO LOAD – ±mA
Figure 10. ± VISO Supply Voltage vs. Load
5V
10µs
100
90
10
0%
±10V, 15kHz STEP OUTPUT RESPONSE (G=1)
Figure 8. Output Response to Full-Scale Step Input
(G = 1 V/V)
–6–
REV. 0
AD215
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/VOUT) will flow out of the 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.
AD2151
AD215N
37
OUT LON
37
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.
RIN = 2kΩ
1
RF
VSIGNAL
ANALOG STAR GROUND
RG
OUT LO1
CF
47pF
3
4
2
SIG COM
IN+
IN–
FB
IN COM
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
TRIM
42
42
43
+VIN
PWR RTN
43
AD215
+15V dc
2.2µF
COM
–VIN
44
44
NTH CHANNEL
1ST CHANNEL
38
37
OUT HI
OUT LO
36
43
COM
PWR
RTN
2.2µF
Figure 13. Noninverting Input Configuration for
Gain > 1 V/V
–15V dc
In this circuit, the gain equation is as follows:
VO = (1 + RF/RG) × VSIG
Figure 11. Typical Power Supply Connections
where:
Power Supply Voltage Considerations
VO
VSIG
RF
RG
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.
= Output Voltage (V)
= Input Signal Voltage (V)
= Feedback Resistor Value (Ω)
= Gain Resistor Value (Ω)
Note: Power supply voltages greater than ±17.5 V dc may damage
the internal components and consequently should not be used.
The values for resistors RF and RG are subject to the following
constraints:
USING THE AD215
• The total impedance of the gain network should be less than
10 kΩ.
Unity Gain Input Configuration
The basic unity gain configuration for input signals of up to
± 10 V is shown in Figure 12.
RIN = 2kΩ
1
3
VSIGNAL
4
2
IN+
38
IN–
FB
IN COM
OUTPUT FILTER,
BUFFER AND
TRIM CIRCUITRY
37
TRIM
OUT HI
OUT LO
36
AD215
COM
43
PWR
RTN
• The current drawn in RF is less than 1 mA at ± 10 V. Note that
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 (RF) and gain resistor
(RG).
It is recommended that RF is bypassed with a 47 pF capacitor as
shown.
Note: The 2 kΩ input resistor (RIN) in series with the input
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.
Figure 12. Basic Unity Gain
REV. 0
–7–
AD215
Compensating the Uncommitted Input Op Amp
GAIN AND OFFSET ADJUSTMENTS
General Comments
25
80
20
100
120
15
PHASE
140
10
160
5
GAIN
0
180
–5
200
–10
220
–15
240
–20
260
–25
100k
1M
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).
Ø, EXCESS PHASE – Degrees
AVERAGE VOLTAGE GAIN – dB
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 (RF) and compensation capacitor (CF) to ensure frequency
stability when reactive or nonlinear components are used.
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.
280
100M
10M
FREQUENCY – Hz
• 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.
Figure 14. Open-Loop Gain and Frequency Response
Inverting, Summing or Current Input Configuration
• It is recommended that input offset adjustments are made
prior to gain adjustments.
Figure 14 shows how the AD215 can measure currents or sum
currents or voltages.
4
RF
IS
RS2
RS1
VS2
VS1
CF
47pF
3
1
2
• The AD215 should be allowed to warm up for approximately
10 minutes before gain or offset adjustments are made.
FB
Input Gain Adjustments for Noninverting Mode
IN–
OUT HI
IN+
IN COM
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
TRIM
AD215
Figure 16 shows a suggested noninverting gain adjustment circuit. Note that the gain adjustment potentiometer RP is incorporated into the gain-setting resistor network.
38
OUT LO
37
RIN = 2kΩ
36
1
COM
43
RP
PWR
RTN
VSIGNAL
Figure 15. Noninverting Summing/Current Configuration
RC
3
38
IN–
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
CF
0.47pF
4
RG
IN+
RF
2
FB
IN COM
37
For this circuit, the output voltage equation is:
TRIM
VO = –RF × (IS + VS1/RS1 + VS2/RS2 + . . .)
AD215
V
VS1
VS2
IS
RF
RS1
RS2
= Output Voltage (V)
= Input Voltage Signal 1 (V)
= Input Voltage Signal 2 (V)
= Input Current Source (A)
= Feedback Resistor (Ω) (10 kΩ, typ)
= Input Signal 1 Source Resistance (Ω)
= Input Signal 2 Source Resistance (Ω)
OUT LO
36
43
where:
OUT HI
COM
PWR
RTN
Figure 16. Gain Adjustment for Noninverting Configuration
For a ± 1% trim range:
(RP ≈1kΩ), RC ≈ 0.02 ×
RG × RF
RG + RF
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 VS1, RS1 and RF were connected as shown
with the solid lines, the input voltage span of VS1 could accommodate up to ± 50 V when RF = 10 kΩ and RS1 = 50 kΩ.
–8–
REV. 0
AD215
USING ISOLATED POWER
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
(RP) in the feedback loop. The adjustments are effective for all
gains in the 1 to 10 V/V range.
RIN
RC
RF
4
RF
1kΩ
CF
47pF
3
1
FB
IN–
IN+
38
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
IN COM
AD215
IN–
3
OUT HI
VSIGNAL
2
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.
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
IN+
1
FB
4
IN COM
2
OUT LO
37
TRIM
AD215
38
37
TRIM
LOAD
36
+VS
6
COM
43
+VISO
PWR
RTN
1.5kΩ
C1
6.8µF
1.5kΩ
C2
6.8µF
–VISO
430kHz
POWER
OSCILLATOR
ISOLATED
DC
SUPPLY
5
PWR
RTN
–VS
OUT HI
OUT LO
36
+15V dc
42
2.2µF
43
COM
2.2µF
–15V dc
44
Figure 17. Gain Adjustment for Inverting Configuration
For an approximate ± 1% gain trim range,
Figure 19. Using the Isolated Power Supplies
R × RF
RX = IN
RIN + RF
PCB LAYOUT FOR MULTICHANNEL APPLICATIONS
RC = 0.02 × RIN
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.
and select
while
PWR
RTN
RF < 10 kΩ
CF = 47 pF
Note: RF and RIN should have matched temperature coefficient
drift characteristics.
2.2µF
2.2µF
Output Offset Adjustments
38
36
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.
42
38
36
1
4
2
38
IN+
LOW-PASS OUTPUT
FILTER,
BUFFER
(150kΩ)
FB
42
IN COM
33kΩ
RP2
10kΩ
36
0.01µF
42
44
OUT HI2
TRIM 2
43
38
42
44
ANALOG
STAR
GROUND
OUT HI3
TRIM 3
37
RS
100kΩ
OUT HI1
43
38
36
TRIM
44
TRIM 1
37
OUT HI
RT
1MΩ
OUT HI0
43
37
IN–
44
SUPPLY BYPASS
CAPACITORS FOR
EVERY FOUR
AD215s
TRIM 0
37
36
3
–15V dc
+15V dc
43
2.2µF
2.2µF
OUT LO
37
+15VIN 42
AD215
+15V dc
Figure 20a. PCB Layout for Unity Gain
2.2µF
PWR RTN 43
COM
2.2µF
–15VIN 44
–15V dc
Figure 18. Output Offset Adjustment Circuit
Output Gain Adjustments
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.
Since the output amplifier stage of the AD215 is fixed at unity
gain, any adjustments can be made only in a subsequent stage.
REV. 0
–9–
AD215
When gain setting resistors are used, 0.325" channel centers can
still be achieved as shown in Figure 20b.
RF
CF
IN
IN COM
+VISO
–VISO
2
RG
1
C2
RF
IN COM
+VISO
–VISO
C1
2
RG
1
C1, C2 ARE VISO FILTER CAPACITORS.
C2
5
3
CF
IN
6
4
6
4
5
3
C1
RF, RG ARE FEEDBACK, GAIN RESISTORS.
Figure 20b. PCB Layout for Gain Greater than Unity
APPLICATIONS EXAMPLES
Motor Control
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.
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.
ENCODER FEEDBACK
G=1
4
MOTOR
COMMAND
3
1
±10 VOLTS
2
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 ± VSPAN which is typically
only a few millivolts, rather than the VEXC 4 2 that would be
achieved with a unipolar excitation source and Wheatstone
bridge configuration.
CF IS A FEEDBACK BYPASS CAPACITOR.
AD215
AC Transducer Applications
ISOLATED
MOTOR
IMOTOR
COMMAND
OPTICAL
SHAFT RESOLVER
38
MOTOR
V
±10V
OR
C CONTROL
MOTOR
TACHOMETER
UNIT
37
θ
OUT LO
ENCODER
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).
COM
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.
EN
A1
A0
AD7502
(–15V)
GND
DTL/TTL TO CMOS LEVEL
TRANSLATOR
DECODER/DRIVER
(+15V)
4
3
S1 – S4
S5 – S8
1
2
6
6.8µF
2
6.8µF
5
FB
AD215
G=1
IN–
IN+
OUT HI
38
OUT LO
IN COM
37
+VISO
COM
–VISO
42 +15V
44 –15V
43
PWR
RTN
Figure 22. Multichannel Data Acquisition Application
–10–
REV. 0
AD215
+VISO
+VISO
220Ω
Q1
2N3904
1/2
AD648
–VISO
1MΩ
+1.2V
+VISO
2MΩ
1
–1.2V
500Ω 9.76kΩ
1/2
AD648
–VISO
IN–
IN+
MOD
2.2pF
Q2
2N3906
–VISO
453kΩ
1kΩ
6
C1
6.8µF
C2
6.8µF
2
5
–11–
OUTPUT
FILTER
AND
BUFFER
38 OUT HI
37 OUT LO
36 TRIM
+VISO
42 +15V
COM
–VISO
ISOLATED
DC
SUPPLY
Figure 23. Strain Gage Signal Conditioning Application
REV. 0
DEMOD
AD215
220Ω
AD589
3
AD744
350Ω
–ε
10kΩ
6.8kΩ
FB
4
350Ω
+ε
430kHz
POWER
OSC
44 –15V
43 PWR
RTN
AD215
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
AD215 SIP PACKAGE
0.840
(21.4)
MAX
0.815
(20.7)
0.020 (0.5)
0.015 (0.4)
0.12 (3.0) TYP
0.094 (2.4)
30° TYP
0.16 (4.1)
0.16 (4.1)
0.010
(0.25)
2.15 (54.6)
0.1 (2.5)
0.1 (2.5)
1.50 (38.1)
0.05 (1.3)
1
3
2
5
4
0.165 (4.2)
0.135 (3.4)
0.2
(5.1)
0.250
(6.4)
6
0.11 (2.8)
BOTTOM VIEW OF
FOOTPRINT
0.712 (18.2)
37
43
36 38
42 44
0.712 (18.2)
0.1
(2.5)
0.11 (2.8)
0.022 (0.56)
C
L
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.
PRINTED IN U.S.A.
0.325
(8.3)
MAX
C2134–20–4/96
0.325 (8.3)
MAX
2.480 (63.0) MAX
–12–
REV. 0