AD215BY

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