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FEATURES Isolation Voltage Rating: 1,500 V rms Wide Bandwidth: 120 kHz, Full Power (-3 dB) Rapid Slew Rate: 6 V/ s Fast Settling Time: 9 s Low Harmonic Distortion: -80 dB @ 1 kHz Low Nonlinearity: 0.005% Wide Output Range: 10 V, min (Buffered) Built-in Isolated Power Supply: 15 V dc @ 10 mA Performance Rated over -40 C to +85 C APPLICATIONS INCLUDE High Speed Data Acquisition Systems Power Line and Transient Monitors Multichannel Muxed Input Isolation Waveform Recording Instrumentation Power Supply Controls Vibration Analysis
120 kHz Bandwidth, Low Distortion, Isolation Amplifier AD215
FUNCTIONAL BLOCK DIAGRAM
FB 4 UNCOMMITTED INPUT OP AMP IN- 3 IN+ 1 IN COM 2 MODULATOR T1 DEMODULATOR LOW-PASS FILTER 150kHz OUTPUT BUFFER 36 TRIM 33k 0.01F 37 OUT LO POWER +VISO 6 -VISO 5 ISOLATED DC SUPPLY T2 430kHz POWER OSCILLATOR 42 +15VIN 44 -15VIN 43 PWR RTN SIGNAL R R 38 OUT HI
AD215
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
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 A 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 -40 C to +85 C Temperature Range: With an extended industrial temperature range rating, the AD215 is an ideal isolation solution for use in many industrial environments.
High Speed Dynamic Characteristics: The AD215 features a typical full-power bandwidth of 120 kHz (100 kHz min), rise time of 3 s and settling time of 9 s. The high speed performance of the AD215 allows for unsurpassed galvanic isolation of virtually any wideband dynamic signal.
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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. (c) 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 @ +25 C, V =
S
15 V dc, 2 k
output load, unless otherwise noted.)
Min 1 AD215AY/BY Typ Max 10 2 Units V/V % ppm/C ppm/C ppm/V ppm/mA % % % % V V dB V rms V rms dB dB dB dB dB dB A rms M G pF 2.0 mV V/C V/C mV V/C V/C V/V V/mA nA nA nA nA nV/Hz kHz s V/s 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)
Conditions
G = 1 V/V, No Load on VISO 0C to +85C -40C to 0C (14.5 V dc to 16.5 V dc) 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 G = 1 V/V IN+ or IN-, to IN COM Input to Output, AC, 60 Hz 100% Tested4 100% Tested4 RS 100 (IN+ & IN-), G = 1 V/V, 60 Hz RS 100 (IN+ & IN-), G = 1 V/V, 1 kHz RS 100 (IN+ & IN-), G = 1 V/V, 10 kHz RS 1 k (IN+ & IN-), G = 1 V/V, 60 Hz RS 1 k (IN+ & IN-), G = 1 V/V, 1 kHz RS 1 k (IN+ & IN-), G = 1 V/V, 10 kHz 240 V rms, 60 Hz G = 1 V/V 10
0.5 +15 +50 +100 +20 0.005 0.01 0.01 0.025
0.015 0.025
15 100
1500 750 120 100 80 105 85 65 2 16 2 4.5 0.4 2 20 0 -35 30 80 350 -35 300 400 3 40 20 100 120 2.2 6 3
Leakage Current, Input to Output INPUT IMPEDANCE Differential Common Mode INPUT OFFSET VOLTAGE Initial vs. Temperature OUTPUT OFFSET VOLTAGE Initial vs. Temperature vs. Supply Voltage vs. Isolated Supply Load2 INPUT BIAS CURRENT Initial vs. Temperature INPUT DIFFERENCE CURRENT Initial vs. Temperature INPUT VOLTAGE NOISE Input Voltage Noise DYNAMIC RESPONSE (2 k Load) Full Signal Bandwidth (-3 dB) Transport Delay6 Slew Rate Rise Time
@ +25C 0C to +85C -40C to 0C @ +25C, Trimmable to Zero 0C to +85C -40C to 0C
-80
@ +25C -40C to +85C @ +25C -40C to +85C Frequency > 10 Hz G = 1 V/V, 20 V pk-pk Signal 10 V Output Swing 10% to 90%, 10 V Output Swing
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AD215
Parameter DYNAMIC RESPONSE (2 k 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 TEMPERATURE RANGE Rated Performance Storage Conditions 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 k Load 10 5 500 1 10 2.5 14.25 15 +20 +25 10 -90 290 50 17.25 Min AD215AY/BY Typ Max 9 1 -80 -65 5 10 Units s % dB dB s s V mA pF mV pk-pk mV pk-pk V mV/C mV/C mA mV/V mV/V mV rms V dc V dc mA C C
1 MHz Bandwidth 50 kHz Bandwidth No Load 0C to +85C -40C to 0C No Load to Full Load 1 MHz Bandwidth, No Load2 Rated Performance Operating10 Operating (+15 V dc/-15 V dc Supplies)
14.5 15 16.5 14.25 17 +40/-18 -40 -40 +85 +85
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 F 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 F 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.
WARNING!
ESD SENSITIVE DEVICE
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AD215
FB 4 UNCOMMITTED INPUT OP AMP IN-
3
AD215
SIGNAL LOW-PASS FILTER 150kHz OUTPUT BUFFER
36
R
R
38
IN+ 1 IN COM
2
OUT HI
MODULATOR T1
DEMODULATOR
TRIM
33k POWER +VISO 6 -VISO 5 ISOLATED DC SUPPLY T2 430kHz POWER OSCILLATOR
0.01F
37
OUT LO +15VIN -15VIN PWR RTN
42 44 43
Figure 1. Functional Block Diagram
PIN CONFIGURATIONS
1 2 3 4 5 6 BOTTOM VIEW OF FOOTPRINT 37 36 38 43 42 44
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.
AD215 PIN DESIGNATIONS
Pin 1 2 3 4 5 6 36 37 38 42 43 44
Designation IN+ IN COM IN- FB -VISO OUT +VISO OUT TRIM OUT LO OUT HI +15 VIN PWR RTN -15 VIN
Function 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
ORDERING GUIDE
Model AD215AY AD215BY
Temperature Range -40C to +85C -40C to +85C
VCMV 750 1500
Nonlinearity* 0.01% 0.005%
*Typical @ +25C, G = 1 V/V.
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Performance Characteristics-AD215
0.10 0.05 130 0 GAIN ERROR - %
CMR - dB
150 140
120 110 100 90
RS 100
-0.05 -0.10 -0.15
80 -0.20 -0.25 -40 70 60 10
RS 1k
-20
0
20 40 60 TEMPERATURE - C
80
100
100
1k FREQUENCY - Hz
10k
100k
Figure 2. Gain Error vs. Temperature
Figure 4. Typical Common-Mode Rejection vs. Frequency
1 0 -1
1mV
NONLINEARITY - mV NONLINEARITY - %
100 90
-2 -3 GAIN - dB -4 -5 -6 -7 -8 -9 -10 -11 G=1
+1 0 -1
10 0%
+0.004
-0.004
G = 10
-10 -8
-6 -4 -2 0 2 4 6 OUTPUT VOLTAGE - Volts
8
10
-12 0.1
G = 100 1.0 10 100 INPUT SIGNAL FREQUENCY - kHz 1000
Figure 3. Gain Nonlinearity vs. Output Voltage (G = 1 V/V)
Figure 5. Normalized Gain as a Function of Signal Frequency
TRANSPORT DELAY - s
3 2 1 0 0
G = 100 G =10 G=1
PHASE SHIFT - Degrees
45
90
G=1 G =10 G = 100 10 20 30 40 50 60 70 80 90 100 110 120 FREQUENCY - kHz
130
Figure 6. Phase Shift and Transport Delay vs. Frequency
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AD215-Performance Characteristics
60 56
100 90
52
OUTPUT
100mV
VISO RIPPLE - mV p-p
48 44 40 36 32 28 24 20 16 12 8 4 0
0.33F BYPASS CAPS
5V
10 0%
INPUT (+10V STEP)
1.0F BYPASS CAPS
5s
OVERSHOOT
3.3F BYPASS CAPS
10F BYPASS CAPS 0 1 2 3 4 5 6 VISO LOAD - mA 7 8 9 10
Figure 7a. Overshoot to a Full-Scale Step Input (G = 1 V/V)
Figure 9. VISO Supply Ripple vs. Load
16.2
100 90
16.0
5V
INPUT (-10V STEP)
VISO - V
15.8 15.6 15.4 15.2
VS = 15V dc
100mV
10 0%
OUTPUT
5s
UNDERSHOOT
15.0 14.8
NOTE: THE GAIN AND OFFSET ERRORS WILL INCREASE WHEN THE ISOLATED POWER SUPPLY LOAD EXCEEDS 10mA 5 VISO LOAD - mA 10 15
Figure 7b. Undershoot to a Full-Scale Input (G = 1 V/V)
Figure 10. VISO Supply Voltage vs. Load
5V
100 90
10s
10 0%
10V, 15kHz STEP OUTPUT RESPONSE (G=1)
Figure 8. Output Response to Full-Scale Step Input (G = 1 V/V)
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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.
AD215N
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 = 2k
1 3
IN+ IN- FB IN COM OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY TRIM
38
OUT HI
AD2151
OUT LON
37
ANALOG STAR GROUND OUT LO1 +VIN 2.2F COM -VIN 2.2F -15V dc SIG COM
VSIGNAL RG
RF
CF 47pF
4 2
37 36 43
OUT LO
42
42
+15V dc
AD215
COM PWR RTN
43
43
PWR RTN
44
44
Figure 13. Noninverting Input Configuration for Gain > 1 V/V
NTH CHANNEL
1ST CHANNEL
In this circuit, the gain equation is as follows: VO = (1 + RF/RG) x VSIG where: VO VSIG RF RG = Output Voltage (V) = Input Signal Voltage (V) = Feedback Resistor Value () = Gain Resistor Value ()
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
The values for resistors RF and RG are subject to the following constraints: * The total impedance of the gain network should be less than 10 k. * 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 k 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.
Unity Gain Input Configuration The basic unity gain configuration for input signals of up to 10 V is shown in Figure 12.
RIN = 2k
1 3
IN+ IN- FB IN COM
38
OUT HI
VSIGNAL
4 2
OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY
37
OUT LO
TRIM
36
AD215
43
COM PWR RTN
Figure 12. Basic Unity Gain
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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 (RF) and compensation capacitor (CF) to ensure frequency stability when reactive or nonlinear components are used.
25 20 80 100
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).
AVERAGE VOLTAGE GAIN - dB
PHASE 10 5 GAIN 0 -5 -10 -15 -20 -25 100k 1M 10M FREQUENCY - Hz 180 200 220 240 260 280 100M 140 160
O, EXCESS PHASE - Degrees
15
120
* 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 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.
4
FB IN- IN+ OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY TRIM
38
RF
CF 47pF
3 1
OUT HI
IS
RS2 VS2
RS1 VS1
Figure 16 shows a suggested noninverting gain adjustment circuit. Note that the gain adjustment potentiometer RP is incorporated into the gain-setting resistor network.
RIN = 2k
1
2
IN COM
OUT LO
37 36 43
IN+ IN- OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY
37 38
AD215
COM PWR RTN
OUT HI
RP VSIGNAL RC RG
3
CF 0.47pF
4
FB IN COM
Figure 15. Noninverting Summing/Current Configuration
RF
2
OUT LO
For this circuit, the output voltage equation is: VO = -RF x (IS + VS1/RS1 + VS2/RS2 + . . .)
AD215
TRIM
36 43
COM PWR RTN
where:
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 () (10 k, typ) = Input Signal 1 Source Resistance () = Input Signal 2 Source Resistance ()
Figure 16. Gain Adjustment for Noninverting Configuration
For a 1% trim range:
(RP 1k), RC 0.02 x
RG x 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 k and RS1 = 50 k.
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AD215
Input Gain Adjustments for the Inverting Mode USING ISOLATED POWER
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
FB
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.
IN- IN+ FB IN COM OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY TRIM LOAD +VISO
6
RF 1k
CF 47pF
3 1
IN- IN+ OUTPUT FILTER, BUFFER AND TRIM CIRCUITRY TRIM
38
OUT HI
3 1 4
AD215
38
OUT HI
VSIGNAL
2
IN COM
OUT LO
37 36 43
2
37 36 42
OUT LO
AD215
COM PWR RTN
1.5k 1.5k
+VS ISOLATED DC SUPPLY 430kHz POWER OSCILLATOR PWR RTN -VS
C1 6.8F C2 6.8F
5
+15V dc 2.2F COM
43
-VISO
2.2F
44
Figure 17. Gain Adjustment for Inverting Configuration
-15V dc
For an approximate 1% gain trim range,
R x RF RX = IN RIN + RF
and select RC = 0.02 x RIN while RF < 10 k CF = 47 pF Note: RF and RIN should have matched temperature coefficient drift characteristics.
Output Offset Adjustments
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 -15V dc 2.2F 2.2F 36 37 38 42 37 38 42 37
38
SUPPLY BYPASS CAPACITORS FOR EVERY FOUR AD215s OUT HI0 TRIM 0
38 42 43 44 43 44 43 38 42 37 43 2.2F 2.2F 44 44
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- IN+ FB IN COM 33k LOW-PASS OUTPUT FILTER, BUFFER (150k)
36
OUT HI1 TRIM 1
36
3 1 4 2
OUT HI2 TRIM 2 ANALOG STAR GROUND
OUT HI
36
OUT HI3 TRIM 3
TRIM 0.01F
RT 1M
36
RP2 10k
RS 100k
OUT LO
37
+15VIN 42
+15V dc 2.2F COM 2.2F -15V dc
AD215
Figure 20a. PCB Layout for Unity Gain
CAUTION
PWR RTN 43 -15VIN 44
Figure 18. Output Offset Adjustment Circuit
Output Gain Adjustments
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.
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AD215
When gain setting resistors are used, 0.325" channel centers can still be achieved as shown in Figure 20b.
RF IN IN COM +VISO -VISO RF IN IN COM +VISO -VISO RG RG CF 1 2 4 6
AC Transducer Applications
3
5
C2 CF
C1 2 4 6
1
3
5
C1, C2 ARE VISO FILTER CAPACITORS. RF, RG ARE FEEDBACK, GAIN RESISTORS. CF IS A FEEDBACK BYPASS CAPACITOR.
C2
C1
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 2 that would be 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 A quiescent current) and the high speed AD744 BiFET amplifier (4 mA quiescent current).
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.
ENCODER FEEDBACK
AD215
4 MOTOR COMMAND 10 VOLTS 2 COM 3 1 G=1
ISOLATED MOTOR IMOTOR COMMAND OPTICAL SHAFT RESOLVER 38 MOTOR VC CONTROL 10V OR MOTOR TACHOMETER UNIT 37 OUT LO ENCODER
Figure 21. Motor Control Application
The current drive capabilities of the AD215's bipolar 15 V dc isolated power supply is more than adequate to meet the modest 800 A 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
Multichannel Data Acquisition
AD7502
(-15V) GND (+15V)
4 3
DTL/TTL TO CMOS LEVEL TRANSLATOR DECODER/DRIVER
FB IN- IN+ IN COM
AD215
G=1 OUT HI
38
S1 - S4
S5 - S8
1 2
OUT LO
37
6
+VISO COM -VISO
42 +15V 44 -15V 43
6.8F
2
6.8F
5
PWR RTN
Figure 22. Multichannel Data Acquisition Application
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AD215
+VISO 220 +VISO Q1 2N3904 +1.2V 350 + +VISO 10k 6.8k 500 9.76k 220 350 - -1.2V Q2 2N3906 -VISO 2.2pF -VISO 1M FB
4
1/2 AD648
2M
AD744
3 1
IN- IN+ MOD DEMOD
OUTPUT FILTER AND BUFFER
38 OUT HI
37 OUT LO 36 TRIM
AD215
453k 1k
6
AD589
-VISO
1/2 AD648
+VISO
42 +15V
C1 C2
6.8F
2
COM -VISO
6.8F
5
ISOLATED DC SUPPLY
430kHz POWER OSC
44 -15V 43 PWR
RTN
Figure 23. Strain Gage Signal Conditioning Application
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AD215
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
AD215 SIP PACKAGE
C2134-20-4/96
0.325 (8.3) MAX
2.480 (63.0) MAX
0.815 (20.7)
0.840 (21.4) MAX
0.020 (0.5) 0.015 (0.4) 0.16 (4.1)
0.12 (3.0) TYP 0.094 (2.4) 2.15 (54.6) 0.250 (6.4) 0.2 (5.1) 0.1 (2.5) 1.50 (38.1) 1 3 2 5 4 6 BOTTOM VIEW OF FOOTPRINT 0.712 (18.2) 0.712 (18.2) 37 36 38 43
30 TYP 0.16 (4.1)
0.010 (0.25) 0.165 (4.2) 0.135 (3.4)
0.1 (2.5) 0.11 (2.8) 0.1 (2.5) 0.11 (2.8)
0.05 (1.3) 0.325 (8.3) MAX
42 44
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.
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PRINTED IN U.S.A.

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