AD215BY [ADI]
120 kHz Bandwidth, Low Distortion, Isolation Amplifier; 120 kHz带宽，低失真，隔离放大器
| 型号： | AD215BY |
| 厂家： | 
ADI |
| 描述： | 120 kHz Bandwidth, Low Distortion, Isolation Amplifier |
| 文件： | 总12页 (文件大小：237K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
120 kHz Bandwidth, Low Distortion,
Isolation Amplifier
a
AD215
FEATURES
FUNCTIO NAL BLO CK D IAGRAM
Isolation Voltage Rating: 1,500 V rm s
Wide Bandw idth: 120 kHz, Full Pow er (–3 dB)
Rapid Slew Rate: 6 V/ s
Fast Settling Tim e: 9 s
Low Harm onic Distortion: –80 dB @ 1 kHz
Low Nonlinearity: ؎0.005%
FB
4
AD215
UNCOMMITTED
INPUT OP AMP
SIGNAL
R
R
3
1
IN–
IN+
38 OUT HI
LOW-PASS
FILTER
150kHz
MODULATOR
DEMODULATOR
2
IN COM
OUTPUT
T1
BUFFER
Wide Output Range: ؎10 V, m in (Buffered)
Built-in Isolated Pow er Supply: ؎15 V dc @ ؎10 m A
Perform ance Rated over –40؇C to +85؇C
36
TRIM
33kΩ
0.01µF
37 OUT LO
POWER
T2
+15VIN
+VISO
–VISO
6
5
42
44 –15VIN
43
APPLICATIONS INCLUDE
430kHz
POWER
OSCILLATOR
ISOLATED
DC
SUPPLY
High Speed Data Acquisition System s
Pow er Line and Transient Monitors
Multichannel Muxed Input Isolation
Waveform Recording Instrum entation
Pow er Supply Controls
PWR RTN
Vibration Analysis
Flexible Input and Buffer ed O utput Stages: An uncommit-
ted op amp is provided on the input stage of the AD215 to
allow for input buffering or amplification and signal condition-
ing. T he AD215 also features a buffered output stage to drive
low impedance loads and an output voltage trim for zeroing the
output offset where needed.
GENERAL D ESCRIP TIO N
T he AD215 is a high speed input isolation amplifier designed to
isolate and amplify wide bandwidth analog signals. T he innova-
tive circuit and transformer design of the AD215 ensures wide-
band dynamic characteristics while preserving key dc performance
specifications.
H igh Accur acy: T he 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. T he AD215 provides
designers with complete isolation of the desired signal without
loss of signal integrity or quality.
T he AD215 provides complete galvanic isolation between the
input and output of the device including the user-available
front-end isolated power supplies. T he 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.
Excellent Com m on-Mode P er for m ance: T he 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. T his 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).
T he 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. T he AD215 has a ±10 V input/output
range, a specified gain range of 1 V/V to 10 V/V, a buffered out-
put with offset trim and a user-available isolated front-end
power supply which produces ±15 V dc at ±10 mA.
Isolated P ower : An unregulated isolated power supply of
±15 V dc @ ±10 mA is available at the isolated input port of
the AD215. T his 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.
P RO D UCT H IGH LIGH TS
H igh Speed D ynam ic Char acter istics: T he AD215 features
a typical full-power bandwidth of 120 kHz (100 kHz min), rise
time of 3 µs and settling time of 9 µs. T he high speed perfor-
mance of the AD215 allows for unsurpassed galvanic isolation
of virtually any wideband dynamic signal.
Rated P er for m ance over the –40؇C to +85؇C Tem per atur e
Range: With an extended industrial temperature range rating,
the AD215 is an ideal isolation solution for use in many indus-
trial environments.
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703
(Typical @ +25؇C, V = ؎15 V dc, 2 k⍀ output load, unless otherwise noted.)
S
AD215–SPECIFICATIONS
AD 215AY/BY
P aram eter
Conditions
Min
Typ
Max
Units
GAIN
Range1
Error
1
10
±2
V/V
%
ppm/°C
ppm/°C
ppm/V
ppm/mA
G = 1 V/V, No Load on VISO
0°C to +85°C
–40°C to 0°C
±0.5
+15
+50
+100
+20
vs. T emperature
vs. Supply Voltage
vs. Isolated Supply Load2
Nonlinearity3
±(14.5 V dc to 16.5 V dc)
AD215BY Grade
±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
±0.015
± 0.025
%
%
%
%
AD215AY Grade
±0.025
INPUT VOLT AGE RAT INGS
Input Voltage Rating
G = 1 V/V
±10
V
Maximum Safe Differential Range
CMRR of Input Op Amp
Isolation Voltage Rating4
AD215BY Grade
IN+ or IN–, to IN COM
±15
100
V
dB
Input to Output, AC, 60 Hz
100% T ested4
1500
750
V rms
V rms
dB
dB
dB
dB
dB
dB
µA rms
AD215AY Grade
100% T ested4
IMRR (Isolation Mode Rejection Ratio) RS ≤ 100 Ω (IN+ & IN–), G = 1 V/V, 60 Hz
RS 100 Ω (IN+ & IN–), G = 1 V/V, 1 kHz
120
100
80
105
85
≤
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
65
Leakage Current, Input to Output
2
INPUT IMPEDANCE
Differential
G = 1 V/V
16
MΩ
Common Mode
2ʈ4.5
GΩʈpF
INPUT OFFSET VOLT AGE
Initial
vs. T emperature
@ +25°C
0°C to +85°C
–40°C to 0°C
±0.4
±2
±20
±2.0
mV
µV/°C
µV/°C
OUT PUT OFFSET VOLT AGE
Initial
vs. T emperature
@ +25°C, T rimmable to Zero
0°C to +85°C
–40°C to 0°C
0
–35
–80
mV
±30
±80
±350
–35
µV/°C
µV/°C
µV/V
µV/mA
vs. Supply Voltage
vs. Isolated Supply Load2
INPUT BIAS CURRENT
Initial
vs. T emperature
@ +25°C
–40°C to +85°C
300
±400
nA
nA
INPUT DIFFERENCE CURRENT
Initial
vs. T emperature
@ +25°C
–40°C to +85°C
±3
±40
nA
nA
INPUT VOLT AGE NOISE
Input Voltage Noise
Frequency > 10 Hz
20
nV/√Hz
DYNAMIC RESPONSE (2 kΩ Load)
Full Signal Bandwidth (–3 dB)
T ransport Delay6
Slew Rate
Rise T ime
G = 1 V/V, 20 V pk-pk Signal
100
120
2.2
6
kHz
µs
V/µs
µs
±10 V Output Swing
10% to 90%, ±10 V Output Swing
3
–2–
REV. 0
AD215
AD 215AY/BY
Typ
P aram eter
Conditions
Min
Max
Units
DYNAMIC RESPONSE (2 kΩ Load) Cont.
Settling T ime
to ±0.10%, ±10 V Output Swing
9
µs
Overshoot
1
%
Harmonic Distortion Components
@ 1 kHz
@ 10 kHz
G = 1 V/V, ±15 V Drive
G > 5
–80
–65
5
dB
dB
µs
Overload Recovery T ime
Output Overload Recovery T ime
10
µs
RAT ED OUT PUT
Voltage
Current
Out HI to Out LO
2 kΩ Load
±10
±5
V
mA
Max Capacitive Load
Output Resistance
Output Ripple and Noise7
500
1
10
2.5
pF
Ω
mV pk-pk
mV pk-pk
1 MHz Bandwidth
50 kHz Bandwidth
ISOLAT ED POWER OUT PUT8
Voltage
No Load
±14.25 ±15
±17.25
V
vs. T emperature
0°C to +85°C
–40°C to 0°C
+20
+25
±10
–90
290
50
mV/°C
mV/°C
mA
mV/V
mV/V
mV rms
Current at Rated Supply Voltage2, 9
Regulation
Line Regulation
Ripple
No Load to Full Load
1 MHz Bandwidth, No Load2
POWER SUPPLY
Supply Voltage
Rated Performance
±14.5 ±15
±14.25
±16.5
±17
V dc
V dc
mA
Operating10
Current
Operating (+15 V dc/–15 V dc Supplies)
+40/–18
T EMPERAT URE RANGE
Rated Performance
Storage
–40
–40
+85
+85
°C
°C
NOT ES
11T he gain range of the AD215 is specified from 1 to 10 V/V. T he 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.
12When 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.
13Nonlinearity is specified as a percent (of full-scale range) deviation from a best straight line.
14T he 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.
15T he AD215 should be allowed to warm up for approximately 10 minutes before any gain and/or offset adjustments are made.
16Equivalent to a 0.8 degrees phase shift.
17With the ±15 V dc power supply pins bypassed by 2.2 µF capacitors at the AD215 pins.
18Caution: T he 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.
19With 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.
10Voltages 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.
CAUTIO N
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. T herefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
–3–
REV. 0
AD215
4
FB
AD215
UNCOMMITTED
INPUT OP AMP
SIGNAL
R
R
IN–
IN+
3
1
38
OUT HI
LOW-PASS
FILTER
150kHz
MODULATOR
DEMODULATOR
2
IN COM
OUTPUT
BUFFER
T1
36
37
TRIM
33kΩ
0.01µF
OUT LO
POWER
42
44
43
+V
+15V
IN
6
5
ISO
430kHz
POWER
OSCILLATOR
ISOLATED
DC
SUPPLY
–15V
IN
–V
PWR RTN
ISO
T2
Figure 1. Functional Block Diagram
INSID E TH E AD 215
P IN CO NFIGURATIO NS
T he 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 sig-
nals ranging in frequency from true dc values to those having
frequencies of 120 kHz or less.
1
37
3
43
44
5
BOTTOM VIEW OF
FOOTPRINT
4
2
36 38
6
42
T o 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, T 2. T he
resultant voltage developed across the secondary winding is
then rectified and filtered for use as the isolated power supply.
AD 215 P IN D ESIGNATIO NS
P in
D esignation
IN+
IN COM
IN–
Function
1
2
3
4
5
6
36
37
38
42
43
44
Noninverting Input
Input Common
Inverting Input
T his 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 amplifica-
tion or signal conditioning is required.
FB
Amplifier Feedback
–VISO OUT
+VISO OUT
T RIM
OUT LO
OUT HI
+15 VIN
PWR RT N
–15 VIN
Isolated –15 V dc Power Supply
Isolated +15 V dc Power Supply
Output Offset T rim Adjust
Output Low
Output High
+15 V dc Power
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 T 1.
±15 V dc Power Supply Common
–15 V dc Power
T he 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. T he func-
tion of the filter reconstructs the original signal as it appears on
the input.
O RD ERING GUID E
Tem perature Range VCMV
Model
Nonlinearity*
T he signal transformer design and construction allow non-
linearity to be independent of both the specified temperature
and gain ranges.
AD215AY –40°C to +85°C
AD215BY –40°C to +85°C
750
1500
0.01%
0.005%
After complete reconstruction, the signal is subjected to an off-
set trim stage and final output buffer. T he trim circuit allows
the designer flexibility to adjust for any offset as desired.
*T ypical @ +25°C, G = 1 V/V.
–4–
REV. 0
Performance Characteristics–AD215
150
140
130
0.10
0.05
R
≤ 100Ω
S
0
120
110
100
90
–0.05
–0.10
–0.15
–0.20
–0.25
R
≤ 1kΩ
S
80
70
60
10
100
1k
FREQUENCY – Hz
10k
100k
–40
–20
0
20
40
60
80
100
TEMPERATURE – °C
Figure 4. Typical Com m on-Mode Rejection vs. Frequency
Figure 2. Gain Error vs. Tem perature
1
0
–1
–2
–3
–4
–5
–6
1mV
100
90
+0.004
–0.004
+1
0
–7
–1
G = 1
–8
10
0%
–9
G = 10
–10
–11
G = 100
–10 –8 –6 –4 –2
0
2
4
6
8
10
–12
0.1
OUTPUT VOLTAGE – Volts
1.0
10
100
1000
INPUT SIGNAL FREQUENCY – kHz
Figure 5. Norm alized Gain as a Function of Signal
Frequency
Figure 3. Gain Nonlinearity vs. Output Voltage (G = 1 V/V)
G = 100
G =10
G = 1
3
2
1
0
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
–5–
REV. 0
AD215–Performance Characteristics
60
56
52
48
44
40
36
32
28
24
20
16
12
8
100
0.33µF BYPASS CAPS
OUTPUT
90
100mV
INPUT
(+10V STEP)
5V
1.0µF BYPASS CAPS
10
0%
5µs
3.3µF BYPASS CAPS
OVERSHOOT
10µF BYPASS CAPS
4
0
0
1
2
3
4
5
6
7
8
9
10
Figure 7a. Overshoot to a Full-Scale Step Input
(G = 1 V/V)
V
LOAD – mA
ISO
Figure 9. ±VISO Supply Ripple vs. Load
16.2
100
90
16.0
15.8
15.6
5V
INPUT
(–10V STEP)
V
= ±15V dc
S
100mV
10
OUTPUT
15.4
15.2
0%
NOTE:
THE GAIN AND
OFFSET ERRORS
WILL INCREASE
WHEN THE
5µs
UNDERSHOOT
15.0
14.8
ISOLATED
POWER SUPPLY
LOAD EXCEEDS
±10mA
Figure 7b. Undershoot to a Full-Scale Input
(G = 1 V/V)
5
10
15
V
LOAD – ±mA
ISO
Figure 10. ±VISO Supply Voltage vs. Load
10µs
5V
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
P O WERING TH E AD 215
Noninver ting Configur ation for Gain Gr eater Than Unity
Figure 13 shows how to achieve a gain greater than one while
continuing to preserve a very high input impedance. A recom-
mended PC board layout for multichannel applications is shown
in Figure 20b.
T he 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). T herefore, 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.
R
= 2kΩ
IN
IN+
IN–
1
3
OUT HI
38
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
C
F
AD215
R
F
AD215
1
V
N
SIGNAL
47pF
FB
ANALOG STAR GROUND
OUT LO
4
2
R
G
OUT LO
OUT LO
1
IN COM
N
37
42
43
37
37
42
43
44
SIG COM
TRIM
36
43
+V
IN
+15V dc
AD215
COM
2.2µF
2.2µF
PWR
RTN
PWR RTN
IN
COM
–V
–15V dc
44
Figure 13. Noninverting Input Configuration for
Gain > 1 V/V
TH
ST
CHANNEL
N
CHANNEL
1
In this circuit, the gain equation is as follows:
VO = (1 + RF/RG) × VSIG
where:
Figure 11. Typical Power Supply Connections
P ower Supply Voltage Consider ations
VO = Output Voltage (V)
VSIG = Input Signal Voltage (V)
T he 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 op-
erating properly.
RF
= Feedback Resistor Value (Ω)
RG = Gain Resistor Value (Ω)
T he values for resistors RF and RG are subject to the following
constraints:
Note: Power supply voltages greater than ±17.5 V dc may damage
the internal components and consequently should not be used.
• T he total impedance of the gain network should be less than
10 kΩ.
USING TH E AD 215
Unity Gain Input Configur ation
T he basic unity gain configuration for input signals of up to
±10 V is shown in Figure 12.
• T he 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).
R
= 2kΩ
IN
IN+
1
3
4
2
OUT HI
38
IN–
OUTPUT FILTER,
BUFFER AND
TRIM CIRCUITRY
V
It is recommended that RF is bypassed with a 47 pF capacitor as
shown.
SIGNAL
FB
OUT LO
IN COM
37
36
43
TRIM
Note: T he 2 kΩ input resistor (RIN) in series with the input
signal source and the IN+ terminal in Figures 12 and 13 is rec-
ommended to limit the current at the input terminals of the to
5.0 mA when the AD215 is not powered.
AD215
COM
PWR
RTN
Figure 12. Basic Unity Gain
–7–
REV. 0
AD215
Com pensating the Uncom m itted Input O p Am p
GAIN AND O FFSET AD JUSTMENTS
T he open-loop gain and phase versus frequency for the uncom-
mitted input op amp are given in Figure 14. T hese curves can
be used to determine appropriate values for the feedback resis-
tor (RF) and compensation capacitor (CF) to ensure frequency
stability when reactive or nonlinear components are used.
Gener al Com m ents
T he AD215 features an output stage T RIM pin useful for zero-
ing the output offset voltage through use of user supplied circuitry.
When gain and offset adjustments are required, the actual com-
pensation circuit ultimately used depends on the following:
25
20
15
10
5
80
• T he input configuration mode of the isolation amplifier (non-
inverting or inverting).
100
120
140
160
180
200
220
240
260
280
• T he placement of any adjusting potentiometer (on the
isolator’s input or output side).
PHASE
As a general rule:
GAIN
• Gain adjustments should be accomplished at the gain-setting
resistor network at the isolator’s input.
0
–5
–10
–15
• T o 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.
–20
–25
100k
1M
10M
FREQUENCY – Hz
100M
• Output adjustments may be necessary where adjusting poten-
tiometers placed near the input would present a hazard to the
user due to the presence of high common-mode voltages dur-
ing the adjustment procedure.
Figure 14. Open-Loop Gain and Frequency Response
Inver ting, Sum m ing or Cur r ent Input Configur ation
Figure 14 shows how the AD215 can measure currents or sum
currents or voltages.
• It is recommended that input offset adjustments are made
prior to gain adjustments.
• T he AD215 should be allowed to warm up for approximately
10 minutes before gain or offset adjustments are made.
FB
4
C
47pF
F
R
F
Input Gain Adjustm ents for Noninver ting Mode
IN–
IN+
3
1
OUT HI
Figure 16 shows a suggested noninverting gain adjustment cir-
cuit. Note that the gain adjustment potentiometer RP is incorpo-
rated into the gain-setting resistor network.
38
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
R
R
S1
S2
I
S
V
V
S1
S2
OUT LO
IN COM
2
37
TRIM
R
= 2kΩ
IN
IN+
IN–
36
43
1
3
OUT HI
AD215
COM
38
R
OUTPUT
FILTER,
BUFFER
AND
PWR
RTN
P
C
F
0.47pF
R
C
FB
V
4
2
SIGNAL
TRIM
R
F
R
CIRCUITRY
Figure 15. Noninverting Sum m ing/Current Configuration
G
OUT LO
IN COM
37
For this circuit, the output voltage equation is:
TRIM
36
43
AD215
COM
VO = –RF × (IS + VS1/RS1 + VS2/RS2 + . . .)
PWR
RTN
where:
V
= Output Voltage (V)
VS1 = Input Voltage Signal 1 (V)
VS2 = Input Voltage Signal 2 (V)
Figure 16. Gain Adjustm ent for Noninverting Configuration
For a ±1% trim range:
IS
= Input Current Source (A)
RF
= Feedback Resistor (Ω) (10 kΩ, typ)
RG × RF
(RP ≈1kΩ), RC ≈ 0.02 ×
RG + RF
RS1 = Input Signal 1 Source Resistance (Ω)
RS2 = Input Signal 2 Source Resistance (Ω)
T he 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 accom-
modate up to ±50 V when RF = 10 kΩ and RS1 = 50 kΩ.
–8–
REV. 0
AD215
USING ISO LATED P O WER
Input Gain Adjustm ents for the Inver ting 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. T he adjustments are effective for all
gains in the 1 to 10 V/V range.
Each AD215 provides an unregulated, isolated bipolar power
source of ±15 V dc @ ±10 mA, referred to the input common.
T his source may be used to power various ancillary components
such as signal conditioning and/or adjustment circuitry, refer-
ences, op amps or remote transducers. Figure 19 shows typical
connections.
R
R
R
F
IN
C
FB
4
C
F
47pF
AD215
IN–
R
1kΩ
IN–
IN+
F
3
OUT HI
3
1
OUT HI
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
38
IN+
38
37
OUTPUT
FILTER,
BUFFER
AND
TRIM
CIRCUITRY
1
FB
4
2
V
SIGNAL
IN COM
OUT LO
37
36
42
OUT LO
IN COM
2
TRIM
TRIM
LOAD
1.5kΩ
1.5kΩ
36
43
+V
ISO
+V
S
6
5
+15V dc
COM
AD215
COM
C1
6.8µF
PWR
RTN
430kHz
2.2µF
2.2µF
PWR
RTN
ISOLATED
DC
SUPPLY
POWER
OSCIL-
LATOR
43
44
C2
6.8µF
–V
–V
S
ISO
–15V dc
Figure 17. Gain Adjustm ent for Inverting Configuration
For an approximate ±1% gain trim range,
Figure 19. Using the Isolated Power Supplies
RIN × RF
RX
=
RIN + RF
P CB LAYO UT FO R MULTICH ANNEL AP P LICATIO NS
T he 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
RC = 0.02 × RIN
PWR
RTN
RF < 10 kΩ
CF = 47 pF
–15V dc
2.2µF
+15V dc
SUPPLY BYPASS
CAPACITORS FOR
EVERY FOUR
AD215s
Note: RF and RIN should have matched temperature coefficient
drift characteristics.
2.2µF
42
38
38
OUT HI
0
36
36
O utput O ffset Adjustm ents
44
44
44
TRIM
0
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 correc-
tion of 0 mV to +73 mV. T his results in a total output offset
range of approximately –35 mV to +38 mV.
37
37
43
43
OUT HI
1
42
TRIM
1
38
38
OUT HI
2
36
36
42
42
TRIM
ANALOG
STAR
2
37
37
IN–
3
1
43
43
OUT HI
GROUND
38
36
IN+
FB
OUT HI
3
LOW-PASS
FILTER,
(150kΩ)
44
OUTPUT
BUFFER
R
T
1MΩ
TRIM
3
4
2
R
TRIM
P2
10kΩ
IN COM
R
S
2.2µF
33kΩ
0.01µF
100kΩ
2.2µF
OUT LO
37
+15V
IN
42
43
44
+15V dc
COM
–15V dc
Figure 20a. PCB Layout for Unity Gain
CAUTIO N
2.2µF
2.2µF
AD215
PWR RTN
–15V
IN
T he 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.
Figure 18. Output Offset Adjustm ent Circuit
O utput Gain Adjustm ents
Since the output amplifier stage of the AD215 is fixed at unity
gain, any adjustments can be made only in a subsequent stage.
–9–
REV. 0
AD215
When gain setting resistors are used, 0.325" channel centers can
still be achieved as shown in Figure 20b.
AC Tr ansducer 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 distor-
tion. 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).
RF
CF
2
6
4
IN
IN COM
+VISO
RG
1
5
3
–V SO
I
C2
CF
C1
RF
2
6
4
IN
IN COM
RG
1
5
3
+VISO
–V SO
I
C1, C2 ARE VISO FILTER CAPACITORS.
RF, RG ARE FEEDBACK, GAIN RESISTORS.
CF IS A FEEDBACK BYPASS CAPACITOR.
C2
C1
T o alleviate the need for an instrumentation amplifier, the
bridge is powered by a bipolar excitation source. Under this ap-
proach the common-mode voltage is ±VSPAN which is typically
only a few millivolts, rather than the VEXC Ϭ 2 that would be
achieved with a unipolar excitation source and Wheatstone
bridge configuration.
Figure 20b. PCB Layout for Gain Greater than Unity
AP P LICATIO NS EXAMP LES
Motor Contr ol
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 applica-
tion. Its excellent phase characteristics and wide bandwidth are
ideal for this type of application.
ENCODER FEEDBACK
AD215
ISOLATED
MOTOR
G = 1
4
T he low voltage excitation is used to permit the front-end cir-
cuitry to be powered from the isolated power supplies of the
AD215, which can supply up to ±10 mA of isolated power at
±15 V. T he bridge draws only 3.5 mA, leaving sufficient cur-
rent to power the micropower dual BiFET (400 µA quiescent
current) and the high speed AD744 BiFET amplifier (4 mA
quiescent current).
I
MOTOR
COMMAND
MOTOR
COMMAND
OPTICAL
RESOLVER
OR
3
1
SHAFT
38
MOTOR
CONTROL
UNIT
V
±10V
C
MOTOR
TACHOMETER
ENCODER
±10 VOLTS
37
θ
OUT LO
2
COM
Figure 21. Motor Control Application
Multichannel D ata Acquisition
T he 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 multi-
plexer. Digital isolation techniques should be employed to iso-
late the Enable (EN), A0 and A1 logic control signals.
EN
A1
A0
AD7502
(–15V)
DTL/TTL TO CMOS LEVEL
TRANSLATOR
GND
DECODER/DRIVER
(+15V)
AD215
G = 1
FB
4
3
1
IN–
IN+
OUT HI
38
37
S5 – S8
S1 – S4
OUT LO
IN COM
2
+V
ISO
6
2
42 +15V
6.8µF
6.8µF
COM
–15V
44
43
–V
ISO
PWR
RTN
5
Figure 22. Multichannel Data Acquisition Application
–10–
REV. 0
AD215
+V
ISO
+V
ISO
220Ω
Q1
–V
ISO
2N3904
1/2
AD648
1MΩ
+1.2V
FB
4
3
1
350Ω
38 OUT HI
IN–
IN+
OUTPUT
FILTER
AND
2MΩ
+ε
AD744
MOD
DEMOD
+V
350Ω
ISO
BUFFER
–ε
OUT LO
TRIM
37
36
10kΩ
2.2pF
6.8kΩ
–1.2V
Q2
500Ω 9.76kΩ
AD215
220Ω
2N3906
+V
453kΩ
1/2
AD648
ISO
6
+15V
AD589
42
1kΩ
–V
ISO
–V
ISO
C1
C2
6.8µF
6.8µF
ISOLATED
DC
SUPPLY
430kHz
POWER
OSC
COM
44 –15V
2
5
–V
ISO
43 PWR
RTN
Figure 23. Strain Gage Signal Conditioning Application
–11–
REV. 0
AD215
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
AD 215 SIP P ACKAGE
0.325 (8.3)
MAX
2.480 (63.0) MAX
0.840
(21.4)
MAX
0.815
(20.7)
0.020 (0.5)
0.015 (0.4)
0.12 (3.0) TYP
°
30 TYP
0.094 (2.4)
0.165 (4.2)
0.135 (3.4)
0.16 (4.1)
0.16 (4.1)
0.010
(0.25)
2.15 (54.6)
0.2
(5.1)
0.250
(6.4)
0.1 (2.5)
0.1 (2.5)
1.50 (38.1)
0.05 (1.3)
0.11 (2.8)
43
37
0.325
(8.3)
MAX
1
2
5
0.1
(2.5)
BOTTOM VIEW OF
FOOTPRINT
3
4
6
42 44
36 38
0.11 (2.8)
0.712 (18.2)
0.712 (18.2)
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.
–12–
REV. 0
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