Optically-Coupled Linear ISOLATION AMPLIFIER

Transcription

1 Optically-Coupled Linear ISOLATION AMPLIFIER FEATURES EASY TO USE, SIMILAR TO AN OP AMP /I IN =, Current Input /V IN = /R IN, Voltage Input % TESTED FOR BREAKDOWN: 5V Continuous Isolation Voltage ULTRA-LOW LEAKAGE:.µA, max, at 4V/6Hz WIDE BANDWIDTH: 6kHz -PIN DIP PACKAGE DESCRIPTION The is an optically-coupled isolation amplifier. High accuracy, linearity, and time-temperature stability are achieved by coupling light from an LED back to the input (negative feedback) as well as forward to the output. Optical components are carefully matched and the amplifier is actively laser-trimmed to assure excellent tracking and low offset errors. The circuit acts as a current-to-voltage converter with a minimum of 5V (5V test) between input and output terminals. It also effectively breaks the galvanic connection between input and output commons as indicated by the ultra-low 6Hz leakage current of.µa at 5V. Voltage input operation is easily achieved by using one external resistor. Versatility along with outstanding DC and AC performance provide excellent solutions to a variety of challenging isolation problems. For example, the is capable of operating in many modes, including: noninverting (unipolar and bipolar) and inverting (unipolar and bipolar) configurations. Two precision current sources are provided to accomplish bipolar operation. Since these are not required for unipolar operation, they are available for external use (see Applications section). APPLICATIONS INDUSTRIAL PROCESS CONTROL Transducer Sensing (Thermocouples, RTD, Pressure Bridges) 4mA to ma Loops Motor and SCR Control Ground Loop Elimination BIOMEDICAL MEASUREMENTS TEST EQUIPMENT DATA ACQUISITION Designs using the are easily accomplished with relatively few external components. Since of the is simply I IN, gains can be changed by altering one resistor value. In addition, the has sufficient bandwidth (DC to 6kHz) to amplify most industrial and test equipment signals. In In Balance I REF 6 4 A D D LED Balance I REF 5 6 A 4 V CC V CC Output V Input CC V CC Common Common International Airport Industrial Park Mailing Address: PO Box 4, Tucson, AZ 54 Street Address: 6 S. Tucson Blvd., Tucson, AZ 56 Tel: (5) 46- Twx: -5- Internet: FAXLine: () 54-6 (US/Canada Only) Cable: BBRCORP Telex: FAX: (5) - Immediate Product Info: () 54-6 Burr-Brown Corporation PDS-456G Printed in U.S.A. August,

2 SPECIFICATIONS ELECTRICAL At T A = 5 C and ±V CC = VDC, unless otherwise specified. AP BP CP PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS ISOLATION Voltage Rated Continuous, AC peak or DC () 5 V Test Breakdown, DC s 5 V Rejection () DC 5 pa/v R IN = kω, Gain = 46 db AC 6Hz, 4V, = 4 pa/v R IN = kω, Gain = db Impedance.5 Ω pf Leakage Current 4Vrms, 6Hz. µa, rms OFFSET VOLTAGE (RTI) Input Stage (V OSI ) Initial Offset 5 µv vs Temperature 5 µv/ C vs Input Power Supplies 5 db vs Time µv/khr Output Stage (V OSO ) Initial Offset 5 µv vs Temperature 5 µv/ C vs Output Power Supplies 5 db vs Time µv/khr Common-Mode Rejection Ratio () 6Hz, = na/v R IN = kω, Gain = db Common-Mode Range ± V REFERENCE CURRENT SOURCES Magnitude Nominal.5.5 µa vs Temperature ppm/ C vs Power Supplies. na/v Matching Nominal 5 na vs Temperature ppm/ C vs Power Supplies. na/v Compliance Voltage V Output Resistance x Ω FREQUENCY RESPONSE Small Signal Bandwidth Gain = V/µA 6 khz Full Power Bandwidth Gain = V/µA, V O = ±V 5 khz Slew Rate.. V/µs Settling Time.% µs TEMPERATURE RANGE Specification 5 5 C Operating 4 C Storage 4 C UNIPOLAR OPERATION GENERAL PARAMETERS Input Current Range Linear Operation. µa Without Damage ma Input Impedance. Ω Output Voltage Swing R L = kω, = V Output Impedance DC, Open-Loop Ω GAIN V O = (I IN ) Initial Error (adjustable to zero) 5 % of FS vs Temperature %/ C vs Time.5 %/khr Nonlinearity () % CURRENT NOISE I IN =.µa.hz to Hz pap-p Hz pa/ Hz Hz. pa/ Hz khz.65 pa/ Hz

3 SPECIFICATIONS (CONT) ELECTRICAL At T A = 5 C and ±V CC = VDC, unless otherwise specified. AP BP CP PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX MIN TYP MAX UNITS INPUT OFFSET CURRENT (I OS ) Initial Offset na vs Temperature.5 na/ C vs Power Supplies. na/v vs Time pa/khr POWER SUPPLIES Input Stage Voltage (rated performance) ± V Voltage (derated performance) ± ± V Supply Current I IN =. µa ±. ± ma I IN = µa,., ma Output Stage Voltage (rated performance) ± V Voltage (derated performance) ± ± V Supply Current V O = ±. ± ma Short Circuit Current Limit ±4 ma BIPOLAR OPERATION GENERAL PARAMETERS Input Current Range Linear Operation µa Without Damage ma Input Impedance. Ω Output Voltage Swing R L = kω, = V Output Impedance Ω GAIN V O = (I IN ) Initial Error (Adjustable To Zero) 5 % of FS vs Temperature %/ C vs Time.5 %/khr Nonlinearity () % CURRENT NOISE I IN =.µa.hz to Hz.5 na, p-p Hz pa/ Hz Hz pa/ Hz khz 6 pa/ Hz INPUT OFFSET CURRENT (I OS, bipolar (4) ) Initial Offset 4 5 na vs Temperature na/ C vs Power Supplies. na/v vs Time 5 pa/khr POWER SUPPLIES Input Stage Voltage (rated performance) ± V Voltage (derated performance) ± ± V Supply Current I IN = µa,., ma I IN = µa,., ma Output Stage Voltage (rated performance) ± V Voltage (derated performance) ± ± V Supply Current V O = ±. ± ma Short Circuit Current Limit ±4 ma Same as AP. NOTES: () See Typical Performance Curves for temperature effects. () See Theory of Operation section for definitions. For db see Ex., CM and HV errors. () Nonlinearity is the peak deviation from a best fit straight line expressed as a percent of full scale output. (4) Bipolar offset current includes effects of reference current mismatch and unipolar offset current. The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes no responsibility for the use of this information, and all use of such information shall be entirely at the user s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant any BURR-BROWN product for use in life support devices and/or systems.

4 PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS Bottom View Input Common NC () Supply Voltages... ±V Isolation Voltage, AC pk or DC... 5V Input Current... ±ma Storage Temperature Range... 4 C to C Lead Temperature (soldering, s)... C Output Short-Circuit Duration... Continuous to Ground In V CC A Ref In Bal Bal V CC A NC () V CC A 6 4 A ORDERING INFORMATION A NOTE: () No internal connection. V CC A Bal Bal Ref Output Common PACKAGE INFORMATION PACKAGE DRAWING PRODUCT PACKAGE NUMBER () AP -Pin Bottom-Braze DIP BP -Pin Bottom-Braze DIP CP -Pin Bottom-Braze DIP NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Burr-Brown recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. USA OEM PRICES PRODUCT PACKAGE TEMPERATURE RANGE AP -Pin Bottom-Braze DIP 5 C to 5 C $5. $4.4 $. BP -Pin Bottom-Braze DIP 5 C to 5 C CP -Pin Bottom-Braze DIP 5 C to 5 C

5 TYPICAL PERFORMANCE CURVES At T A = 5 C, ±V CC = VDC, unless otherwise specified. SMALL SIGNAL FREQUENCY RESPONSE ± BIPOLAR OUTPUT SWING vs ±V CC Amplitude (db) 4 No C F Frequency (khz) C F = 4pF Output Swing (V) ± ± ±5 k Output Stage Power Supply k M (Ω) M ±V CC ±V CC ±V CC V O = (µa) ( ) = V CC.V max M BIPOLAR INPUT STAGE SUPPLY CURRENT vs INPUT CURRENT PHASE SHIFT vs FREQUENCY No C F Supply Current (ma) 5 5 V CC V CC Phase (degrees) C F = 4pF I IN (µa) Frequency (khz) Output Swing (V) 5 UNIPOLAR OUTPUT SWING vs Output Stage Power Supply V O = (µa) ( ) = V CC. V max ±V CC ±V CC ±V CC ±V CC Supply Current (ma) 5 5 V CC UNIPOLAR INPUT STAGE SUPPLY CURRENT vs INPUT CURRENT Short circuit current limit. Not specified for operation in this region. V CC k k M (Ω) M M I IN (µa) 5

6 TYPICAL PERFORMANCE CURVES (CONT) At T A = 5 C, ±V CC = VDC, unless otherwise specified. ISOLATION LEAKAGE CURRENT vs ISOLATION VOLTAGE 5 CONTINUOUS DC ISOLATION VOLTAGE vs TEMPERATURE AC Leakage Current (µarms) Max at 6Hz Typ at 6Hz Typ at DC Isolation Voltage (kv) 5 DC Leakage Current (na) Continuous DC Isolation Voltage (V) Recommended Operating Region 65 C Temperature ( C) 5 C AC Isolation Voltage (Vp) AC ISOLATION VOLTAGE vs TEMPERATURE Recommended Operating Region Temperature ( C) 5 C Rate of Change of Gain Error (%/hr).5.5 RATE OF GAIN ERROR SHIFT vs ISOLATION VOLTAGE Short term shift ( hrs) Long term shift is random. Temp = 5 C Isolation Voltage (VDC) Temp = up to 65 C GAIN ERROR vs TEMPERATURE AND ISOLATION VOLTAGE Gain Error (Normalized to 5 C) V IM >V T V IM < V T T T Temperature ( C) NOTES: V T and T T approximate the threshold for the indicated gain shift. This is caused by the properties of the optical cavity. T T 65 C, V T VDC. Shift does not occur fo AC voltages. V IM = Isolation-Mode Voltage V T = Threshold Voltage T T = Threshold Temperature 6

7 THEORY OF OPERATION The is fundamentally a unity gain current amplifier intended to transfer small signals between electrical circuits separated by high voltages or different references. In most applications, an output voltage is obtained by passing the output current through the feedback resistor ( ). The uses a single light emitting diode (LED) and a pair of photodiode detectors coupled together to isolate the output signal from the input. Figure shows a simplified diagram of the amplifier. I REF and I REF are required only for bipolar operation to generate a midscale reference. The LED and photodiodes (D and D ) are arranged such that the same amount of light falls on each photodiode. Thus, the currents generated by the diodes match very closely. As a result, the transfer function depends upon optical match rather than absolute performance. Laser-trimming of the components improves matching and enhances accuracy, while negative feedback improves linearity. Negative feedback around A occurs through the optical path formed by the LED and D. The signal is transferred across the isolation barrier by the matched light path to D. The overall isolation amplifier is noninverting (a positive going input produces a positive going output). INSTALLATION AND OPERATING INSTRUCTIONS UNIPOLAR OPERATION In Figure, assume a current, I IN, flows out of the (I IN must be negative in unipolar operation). This causes the voltage at pin to decrease. Because the amplifier is inverting, the output of A increases, driving current through the LED. As the LED light output increases, D responds by generating an increasing current. The current increases until the sum of the currents in and out of the input node (Input to A ) is zero. At that point, the negative feedback through D has stabilized the loop, and the current I D equals the input current plus the bias current. As a result, no bias current flows in the source. Since D and D are matched (I D = I D ), I IN is replicated at the output via D. Thus, A functions as a unity-gain current amplifier, and A is a current-to-voltage converter, as described below. Current produced by D must either flow into A or. Since A is designed for low bias current ( na), almost all of the current flows through to the output. The output voltage then becomes: V O = (I D ) = (I D ±I OS ) (I IN ) = I IN () where, I OS is the difference between A and A bias currents. For input voltage operation I IN can be replaced by a voltage source (V IN ) and series resistor (R IN ), since the summing node of the op amp is essentially at ground. Thus, I IN = V IN /R IN. Unipolar operation does have some constraints, however. In this mode the input current must be negative so as to produce a positive output voltage from A to turn the LED on. A current more negative than na is necessary to keep the LED turned on and the loop stabilized. When this condition is not met, the output may be indeterminant. Many sensors generate unidirectional signals, e.g., photoconductive and photodiode devices, as well as some applications of thermocouples. However, other applications do require bipolar operation of the. BIPOLAR OPERATION To activate the bipolar mode, reference currents as shown in Figure are attached to the input nodes of the op amps. The input stage stabilizes just as it did in unipolar operation. I REF 6 Input Circuit Isolation Barrier I REF Output Circuit R IN In A A V IN I IN In Optical Assembly D D LED = I IN Input Common Connect pins and 6 for bipolar, and pins 6 and for unipolar. Output Common Connect pins and for bipolar, and pins and for unipolar. FIGURE. Simplified Block Diagram of the.

8 Assuming I IN =, the photodiode has to supply all the I REF current. Again, due to symmetry, I D = I D. Since the two references are matched, the current generated by D will equal I REF. This results in no current flow in, and the output voltage will be zero. When I IN either adds or subtracts current from the input node, the current D will adjust to satisfy I D = I IN I REF. Because I REF equals I REF and I D equals I D, a current equal to I IN will flow in. The output voltage is then V O = I IN. The range of allowable I IN is limited. Positive I IN can be as large as I REF (.5µA, min). At this point, D supplies no current and the loop opens. Negative I IN can be as large as that generated by D with maximum LED output (recommended µa, max). DC ERRORS Errors in the take the form of offset currents and voltages plus their drifts with temperature. These are shown in Figure. A and A assumed to be ideal amplifiers. V OSO and V OSI the input offset voltages of the output and input stage, respectively. V OSO appears directly at the output, but, V OSI appears at the output as V OSI, R IN see equation (). I OS the offset current. This is the current at the input necessary to make the output zero. It is equal to the combined effect of the difference between the bias currents of A and A and the matching errors in the optical components in the unipolar mode. I REF and I REF reference currents that, when connected to the inputs, enable bipolar operation. The two currents are trimmed, in the bipolar mode, to minimize the I OS BIPOLAR error. I D and I D currents generated by each photodiode in response to the light from the LED. A e gain error. A e = Ideal gain/actual gain () The output then becomes: V IN ± V OS = [( I REF ± I OS )( A e ) I REF ] ±V R IN OSO () The total input referred offset voltage of the can be simplified in the unipolar case by assuming that A e = and V IN = : ±V OSI [ ± I OS UNIPOLAR ] ±V OSO () R IN This voltage is then referred back to the input by dividing by /R IN. V OS (RTI) = (±V OSI ) ±R IN (I OS UNIPOLAR ) V OSO /( /R IN ) (4) Example. Refer to Figure and Electrical Specifications Table. Given: I OS BIPOLAR = 5nA R IN = kω = (gain = ) V OSI = µv V OSO = µv Find: The total offset voltage error referred to the input and output when V IN = V. V OS total RTI = {[±V OSI ±R IN (I OS BIPOLAR ) R IN (I REF )] [ A e ] R IN I REF } ±V OSO /( /R IN ) = {[µv kω (5nA) kω (.5µA)] [.] kω (.5µA]} µv/(/kω) = {[.mv.5mv.5v] [.].5V}.mV =.mv V OS total RTO = V OS total RTI x /R IN =.mv x = mv V OSI R IN V OSO Isolation Barrier () A A V IN I D I OS LED I D I REF I REF NOTE: () Use or greater to achieve a full scale output of V. FIGURE. Circuit Model for DC Errors in the.

9 NOTE: This error is dominated by I OS BIPOLAR and the reference current times the gain error (which appears as an offset). The error for unipolar operation is much lower. The error due to offset current can be zeroed using circuits shown in Figures 6 and. The gain error is adjusted by trimming either or R IN. COMMON-MODE AND HIGH VOLTAGE ERRORS Figure shows a model of the that can be used to analyze common-mode and high voltage behavior. V IN R IN V ERR CM V ERR IM V CM Input Common V IM FIGURE. High Voltage Error Model. Isolation Barrier Output Common Definitions of CMR and IMR I OS is defined as the input current required to make the s output zero. CMRR and IMRR in the are expressed as conductances. CMRR defines the relationship between a change in the applied common-mode voltage (V CM ) and the change in I OS required to maintain the amplifier s output at zero: CMRR (I-mode) = I OS / V CM in na/v (5) CMRR (V-mode) = R IN = in V/V (6) IMRR defines the relationship between a change in the applied isolation mode voltage (V IM ) and the change in I OS required to maintain the amplifier s output to zero: I OS IMRR (I-mode) = in pa/v () V IM I OS V CM I OS IMRR (V-mode) = R IN = in V/V () V IM CMRR and IMRR in V/V are a function of R IN. V IM is the voltage between input common and output common. V CM is the common-mode voltage (noise that is present on both input lines, typically 6Hz). C C V ERR CM V CM V ERR IM V IM V ERR is the equivalent error signal, applied in series with the input voltage, which produces an output error identical to that produced by application of V CM and V IM. CMRR and IMRR are the common-mode and isolationmode rejection ratios, respectively. Total Capacitance (C and C ) is distributed along the isolation barrier. Most of the capacitance is coupled to low impedance or noncritical nodes and affects only the leakage current. Only a small capacitance (C ) couples to the input of the second stage, and contributes to IMRR. Example. Refer to Figure and Electrical Specification Table. Given: V CM = VAC peak at 6Hz, V IM = VDC, CMRR = na/v, IMRR = 5pA/V, R IN = kω, = (Gain = ) Find: The error voltage referred to the input and output when V IN = V V ERR RTI = (V CM )(CMRR)(R IN ) (V IM )(IMRR)(R IN ) = V (na/v)(kω) V (5pA/V)(kΩ) =.mv.mv =.4mV V ERR RTO = V ERR RTI ( /R IN ) =.4mV () =4mV (with DC IMRR) NOTE: This error is dominated by the CMRR term. For purposes of comparing CMRR and IMRR directly with db specifications, the following calculations can be performed: CMRR in V/V = CMRR (I-mode)(R IN ) = na/v (kω) =.mv/v CMR = LOG (.mv/v) = db at 6Hz IMRR in V/V = IMRR (I-mode)(R IN ) = 5pA/V(kΩ) =.5µV/V IMR = LOG (.5 x 6 V/V) = 6dB at DC Example. In Example, V IM is an AC signal at 6Hz and 4pA IMRR = V V ERR RTI = V ERR CM V ERR IM =.mv V (4pA/V)(kΩ) =.mv V ERR RTO = mv (with AC IMRR)

10 Example 4. Given: Total error RTO from Examples and as mv worst case. Find: Percent error of V full scale output V ERR TOTAL V FS % Error = x % mv = x % V =.% NOISE ERRORS Noise errors in the unipolar mode are due primarily to the optical cavity. When the full 6kHz bandwidth is not needed, the output noise of the can be limited by either a capacitor, C F, in the feedback loop or by a low-pass filter following the output. This is shown in Figure 4. Noise in the bipolar mode is due primarily to the reference current sources, and can be reduced by the low-pass filters shown in Figure 5. I IN C F f O = f O = π C F R πrc C OPTIONAL ADJUSTMENTS There are two major sources of offset error: offset voltage and offset current. V OSI and V OSO of the input and output amplifiers can be adjusted independently using external potentiometers. An example is shown in Figure. Note that V OSO (5µV, max) appears directly at the output, but V OSI appears at the output multiplied by gain ( /R IN ). In general, V OS is small compared to the effect of I OS (see Example ). To adjust for I OS use a circuit which intentionally unbalances the offset in one direction and then allows for adjustment back to zero. Figure 6 shows how to adjust unipolar errors at zero input. The unipolar amplifier can be used down to zero input if it is made to be slightly bipolar. By sampling the reference current with R 5 and R 6, the minimum current required to keep the input stage in the linear region of operation can be established. R and R are adjusted to cancel the offset created in the input stage. This brings the output to zero, when the input is zero. Although the amplifier can now operate down to zero input voltage, it has only a small portion of the current drain and noise that the true bipolar configuration would have. Adjusting the bipolar errors is illustrated in Figure. Each of the errors are adjusted in turn. With V IN = open,, I OS is trimmed by adjusting R to make the output zero. R G is then adjusted to trim the gain error. The effects of offset voltage are removed by adjusting R 4. R 5 R 6 4kΩ IC I REF Optional Unipolar I OS Adjust. R R kω Pot FIGURE 4. Two Circuit Techniques for Reducing Noise in the Unipolar Mode. I IN In λ I C I REF kω In µf kω 6 µf I C (MAX) I IN I C (MIN) I IN Ideal Shift due to R and R. Shift due to R 5 and R 6. FIGURE 5. Circuit Techniques for Reducing Noise from the Current Sources in the Bipolar Mode. FIGURE 6. Adjusting the Unipolar Amplifier Errors at Zero Input.

11 R R Optional Bipolar I OS Adjust. R 6 V IN.6kΩ R IN R G 5Ω Pot In In λ 4 V I C R 6kΩ R R SOURCE = V IN ( /R ) () V IN NOTE: () Use postitive input voltage only, V IN >> µa x R SOURCE. R 4 kω FIGURE. Unipolar Inverting. FIGURE. Adjusting the Bipolar Errors. BASIC CIRCUIT CONNECTIONS R 6 R SOURCE V IN () = V IN ( /R ) NOTE: () V IN >> µa x R SOURCE. FIGURE. Bipolar Inverting. FIGURE. Unipolar Noninverting. R Shield IN 6 V IN I IN FIGURE. Bipolar Noninverting. = I IN or = V IN ( /R IN ) APPLICATION INFORMATION The small size, low offset and drift, wide bandwidth, ultralow leakage, and low cost, make the ideal for a variety of isolation applications. The basic mode of operation of the will be determined by the type of signal and application. Major points to consider when designing circuits with the.. Input Common (pin ) and In (pin ) should be grounded through separate lines. The Input Common can carry a large DC current and may cause feedback to the signal input.. Use shielded or twisted pair cable at the input for long lines.. Care should be taken to minimize external capacitance across the isolation barrier.

12 4. The distance across the isolation barrier, between external components and conductor patterns, should be maximized to reduce leakage and arcing. 5. Although not an absolute requirement, the use of conformally-coated printed circuit boards is recommended. 6. When in the unipolar mode, the reference currents (pins and 6) must be terminated. I IN should be greater than na to keep internal LED on.. The noise contribution of the reference currents will cause the bipolar mode to be noisier than the unipolar mode.. The maximum output voltage swing is determined by I IN and. V SWING = I IN MAX X. A capacitor (about pf) can be connected across to compensate for peaking in the frequency response. The peaking is caused by the pole generated by and the capacitance at the input of the output amplifier. Figure through show applications of the..µa to µa Photodiode C F may be used to improve frequency response (reduce peaking). 6 Isolation Barrier C.µF R kω 4 C.µF R kω C F V V C V V C p Isolated Power Supply V E V f O = /π C F R.kΩ C.4µF V O = I IN to V V R and R are required to maintain a ma minimum load to the. FIGURE. Two-Port Isolation Photodiode Amplifier Unipolar. R 5kΩ R 5kΩ Sensor Tranducer R R Bridge Excitation V REF = V R R V IN R G 44Ω 4 5 INA X 6 OPA 6 () R kω Input Common I REF () 6 X Output Common C F 4 V V Total Gain = () V V NOTES: () For isolated supplies see Figure. () In this example, the internal precision current reference, I REF, provides bridge excitation. () Pin of the INA must be more negative than mv for linear operation of the with R = kω. FIGURE. Precision Bridge Isolation Amplifier (Unipolar).

13 C F may be used to improve frequency response (reduce peaking). Isolation Barrier f O = /π C F Offsetting Thermocouple R 4 kω V = mv (±Temp) Cold junction compensation not shown. 6 C.µF R kω 4 C.µF R kω C F V V C V V C p Isolated Power Supply V E V R and R are required to maintain a ma minimum load to the. R.kΩ C.4µF V O = I IN (±V) V Gain Adjust V IN V R kω R kω R 4 kω R MΩ V 6 Gain = to C F Approximate input offsetting = to ±.5µA for isolated supplies see Figures and. FIGURE 4. Three-Port Isolation Thermocouple Amplifier (Bipolar). FIGURE. Isolated Test Equipment Amplifier (Unipolar with Offsetting). Input 5V to V R IN 5Ω Span Adjust R R 5kΩ 6 Offset Adjust V ISOLATED For isolated supplies see Figures and. 4 V ISOLATED I OUT 4-mA Siliconix VNAF R 4 5kΩ R Ω R L Calibration procedure:. Set V IN = V. Adjust R for I OUT = ma. Set V IN = 5V 4. Adjust R IN for I OUT = 4mA FIGURE 6. Isolated 4mA to ma Transmitter (Example of an isolated voltage controlled current source).

14 V CC Offset Adjust V IN R IN kω Com 4 V V V (Non ISO) Offset Adjust V CC V CC V IN kω () V IN V IN V O = M [ I IN I IN ] k k Com V CC V CC I IN () Com V CC V CC ±V CC s to input stages of amplifiers I IN Com 4 () 4 Isolated Power Supply 4 V CC V CC V (Non ISO) NOTE: () No additional connections to output amplifiers Note that a variety of input/gain configurations can be used. FIGURE. Four-Port Isolated Summing Amplifier (Unipolar). 4

15 Channel Select OPTO Isolator Gain Select Input Channels IN IN6 IN5 IN4 IN IN IN IN PGA Digital P/S Analog P/S 5V Input Common () V V 6 CP CE C F 4 V V Output Common () NOTE: () For isolated power supplies see Figures and. FIGURE. Multiple Channel Isolation Amplifier (Bipolar) with Programmable Gain (useful in data acquisition systems).

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