Precision Lowest Cost ISOLATION AMPLIFIER

Transcription

1 Precision Lowest Cost ISOLATION AMPLIFIER FEATURES % TESTED FOR HIGH-VOLTAGE BREAKDOWN RATED 5Vrms HIGH IMR: db at Hz.% max NONLINEARITY BIPOLAR OPERATION: V O = ±V -PIN PLASTIC DIP AND -LEAD SOIC EASE OF USE: Fixed Unity Gain Configuration ±.5V to ±V SUPPLY RANGE APPLICATIONS INDUSTRIAL PROCESS CONTROL: Transducer Isolator, Isolator for Thermocouples, RTDs, Pressure Bridges, and Flow Meters, ma to ma Loop Isolation GROUND LOOP ELIMINATION MOTOR AND SCR CONTROL POWER MONITORING PC-BASED DATA ACQUISITION TEST EQUIPMENT DESCRIPTION The is a precision isolation amplifier incorporating a novel duty cycle modulation-demodulation technique. The signal is transmitted digitally across a pf differential capacitive barrier. With digital modulation the barrier characteristics do not affect signal integrity, resulting in excellent reliability and good high frequency transient immunity across the barrier. Both barrier capacitors are imbedded in the plastic body of the package. The is easy to use. No external components are required for operation. The key specifications are.% max nonlinearity, 5kHz signal bandwidth, and µv/ C V OS drift. A power supply range of ±.5V to ±V and quiescent currents of ±5.mA on V S and ±5.5mA on V S make these amplifiers ideal for a wide range of applications. +V S V S V S +V S The is available in -pin plastic DIP and - lead plastic surface mount packages. International Airport Industrial Park Mailing Address: PO Box, Tucson, AZ 5 Street Address: S. Tucson Blvd., Tucson, AZ 5 Tel: (5) - Twx: -5- Internet: FAXLine: () 5- (US/Canada Only) Cable: BBRCORP Telex: - FAX: (5) -5 Immediate Product Info: () 5- Burr-Brown Corporation PDS-5A Printed in U.S.A. September,

2 SPECIFICATIONS At T A = +5 C, V S = V S = ±5V, and R L = kω, unless otherwise noted. P, U PARAMETER CONDITIONS MIN TYP MAX UNITS ISOLATION Rated Voltage, continuous ac Hz 5 Vac % Test () s, 5pc PD Vac Isolation Mode Rejection Hz db Barrier Impedance Ω pf Leakage Current at Hz V ISO = Vrms..5 µarms GAIN V O = ±V Nominal Gain V/V Gain Error ±.5 ±.5 %FSR Gain vs Temperature ± ppm/ C Nonlinearity () ±.5 ±. %FSR INPUT OFFSET VOLTAGE Initial Offset ± ±5 mv vs Temperature ± µv/ C vs Supply ± mv/v Noise µv/ Hz INPUT Voltage Range ± ±.5 V Resistance kω OUTPUT Voltage Range ± ±.5 V Current Drive ±5 ±5 ma Capacitive Load Drive. µf Ripple Voltage () mvp-p FREQUENCY RESPONSE Small Signal Bandwidth 5 khz Slew Rate V/µs Settling Time V O = ±V.% 5 µs.% 5 µs Overload Recovery Time 5 µs POWER SUPPLIES Rated Voltage ±5 V Voltage Range ±.5 ± V Quiescent Current: V S ±5. ±. ma V S ±5.5 ±. ma TEMPERATURE RANGE Specification 5 +5 C Operating 5 +5 C Storage +5 C Thermal Resistance, θ JA C/W θ JC 5 C/W NOTES: () Tested at. X rated, fail on 5pC partial discharge. () Nonlinearity is the peak deviation of the output voltage from the best-fit straight line. It is expressed as the ratio of deviation to FSR. () Ripple frequency is at carrier frequency (5kHz). 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.

3 CONNECTION DIAGRAM Top View P Package Top View U Package +V S +V S V S 5 V S V S V S +V S 5 +V S PACKAGE INFORMATION PACKAGE DRAWING PRODUCT PACKAGE NUMBER () P -Pin Plastic DIP U -Lead Plastic SOIC - NOTE: () For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. ORDERING INFORMATION NONLINEARITY PRODUCT PACKAGE MAX %FSR P -Pin Plastic DIP ±. U -Lead Plastic SOIC ±. ABSOLUTE MAXIMUM RATINGS () Supply Voltage... ±V...±V Continuous Isolation Voltage... 5Vrms Junction Temperature C Storage Temperature C Lead Temperature (soldering, s)... + C Output Short to Common... Continuous NOTE: () Stresses above these ratings may cause permanent damage. 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.

4 TYPICAL PERFORMANCE CURVES At T A = +5 C, and V S = ±5V, unless otherwise noted. SINE RESPONSE (f = khz) SINE RESPONSE (f = khz) Output Voltage (V) + Output Voltage (V) + 5 Time (µs) 5 Time (µs) STEP RESPONSE STEP RESPONSE Output Voltage (V) + Output Voltage (V) + 5 Time (µs) 5 Time (µs).k ISOLATION VOLTAGE vs FREQUENCY Max DC Rating IMR vs FREQUENCY Peak Isolation Voltage k Typical Performance Degraded Performance IMR (db) k k k M M M Frequency (Hz) k k k M Frequency (Hz)

5 TYPICAL PERFORMANCE CURVES (CONT) At T A = +5 C, and V S = ±5V, unless otherwise noted. 5 PSRR vs FREQUENCY ma ma ISOLATION LEAKAGE CURRENT vs FREQUENCY PSRR (db) V S, V S +V S, +V S Leakage Current (rms) ma µa µa µa 5Vrms Vrms k k k M Frequency (Hz).µA k k k M Frequency (Hz) SIGNAL RESPONSE TO INPUTS GREATER THAN 5kHz / khz Frequency Out 5 / (dbm) 5 Frequency Out 5 5k M.5M Input Frequency (Hz) (NOTE: Shaded area shows aliasing frequencies that cannot be removed by a low-pass filter at the output.) 5

6 THEORY OF OPERATION The isolation amplifier uses an input and an output section galvanically isolated by matched pf isolating capacitors built into the plastic package. The input is dutycycle modulated and transmitted digitally across the barrier. The output section receives the modulated signal, converts it back to an analog voltage and removes the ripple component inherent in the demodulation. Input and output sections are fabricated, then laser trimmed for exceptional circuitry matching common to both input and output sections. The sections are then mounted on opposite ends of the package with the isolating capacitors mounted between the two sections. The transistor count of the is 5 transistors. MODULATOR An input amplifier (A, Figure ) integrates the difference between the input current ( /kω) and a switched ±µa current source. This current source is implemented by a switchable µa source and a fixed µa current sink. To understand the basic operation of the modulator, assume that =.V. The integrator will ramp in one direction until the comparator threshold is exceeded. The comparator and sense amp will force the current source to switch; the resultant signal is a triangular waveform with a 5% duty cycle. The internal oscillator forces the current source to switch at 5kHz. The resultant capacitor drive is a complementary duty-cycle modulation square wave. DEMODULATOR The sense amplifier detects the signal transitions across the capacitive barrier and drives a switched current source into integrator A. The output stage balances the duty-cycle modulated current against the feedback current through the kω feedback resistor, resulting in an average value at the pin equal to. The sample and hold amplifiers in the output feedback loop serve to remove undesired ripple voltages inherent in the demodulation process. BASIC OPERATION SIGNAL AND SUPPLY CONNECTIONS Each power supply pin should be bypassed with µf tantalum capacitors located as close to the amplifier as possible. The internal frequency of the modulator/demodulator is set at 5kHz by an internal oscillator. Therefore, if it is desired to minimize any feedthrough noise (beat frequencies) from a DC/DC converter, use a π filter on the supplies (see Figure ). output has a 5kHz ripple of mv, which can be removed with a simple two pole low-pass filter with a khz cutoff using a low cost op amp (see Figure ). The input to the modulator is a current (set by the kω integrator input resistor) that makes it possible to have an input voltage greater than the input supplies, as long as the output supply is at least ±5V. It is therefore possible when using an unregulated DC/DC converter to minimize PSR related output errors with ±5V voltage regulators on the isolated side and still get the full ±V input and output swing. An example of this application is shown in Figure. CARRIER FREQUENCY CONSIDERATIONS The amplifier transmits the signal across the isolation barrier by a 5kHz duty cycle modulation technique. For input signals having frequencies below 5kHz, this system works like any linear amplifier. But for frequencies Isolation Barrier µa pf pf µa pf kω 5pF µa Sense pf Sense µa 5pF kω A A Osc S/H G = S/H G = +V S V S +V S V S FIGURE. Block Diagram.

7 above 5kHz, the behavior is similar to that of a sampling amplifier. The signal response to inputs greater than 5kHz performance curve shows this behavior graphically; at input frequencies above 5kHz the device generates an output signal component of reduced magnitude at a frequency below 5kHz. This is the aliasing effect of sampling at frequencies less than times the signal frequency (the Nyquist frequency). Note that at the carrier frequency and its harmonics, both the frequency and amplitude of the aliasing go to zero. ISOLATION MODE VOLTAGE INDUCED ERRORS IMV can induce errors at the output as indicated by the plots of IMV vs Frequency. It should be noted that if the IMV frequency exceeds 5kHz, the output also will display spurious outputs (aliasing) in a manner similar to that for >5kHz and the amplifier response will be identical to that shown in the Signal Response to Inputs Greater Than 5kHz typical performance curve. This occurs because IMV-induced errors behave like inputreferred error signals. To predict the total error, divide the isolation voltage by the IMR shown in the IMR versus Frequency typical performance curve and compute the amplifier response to this input-referred error signal from the data given in the Signal Response to Inputs Greater Than 5kHz typical performance curve. For example, if a khz Vrms IMR is present, then a total of [( db) + ( db)] x (V) = mv error signal at khz plus a V, khz error signal will be present at the output. HIGH IMV dv/dt ERRORS As the IMV frequency increases and the dv/dt exceeds V/µs, the sense amp may start to false trigger, and the output will display spurious errors. The common-mode current being sent across the barrier by the high slew rate is the cause of the false triggering of the sense amplifier. Lowering the power supply voltages below ±5V may decrease the dv/dt to 5V/µs for typical performance. HIGH VOLTAGE TESTING Burr-Brown Corporation has adopted a partial discharge test criterion that conforms to the German VDE Optocoupler Standards. This method requires the measurement of minute current pulses (<5pC) while applying Vrms, Hz high voltage stress across every isolation barrier. No partial discharge may be initiated to pass this test. This criterion confirms transient overvoltage (. x 5Vrms) protection without damage to the. Lifetest results verify the absence of failure under continuous rated voltage and maximum temperature. This new test method represents the state-of-the art for non-destructive high voltage reliability testing. It is based on the effects of non-uniform fields that exist in heterogeneous dielectric material during barrier degradation. In the case of void non-uniformities, electric field stress begins to ionize the void region before bridging the entire high voltage barrier. The transient conduction of charge during and after the ionization can be detected externally as a burst of.-.µs current pulses that repeat on each ac voltage cycle. The minimum ac barrier voltage that initiates partial discharge is defined as the inception voltage. Decreasing the barrier voltage to a lower level is required before partial discharge ceases and is defined as the extinction voltage. We have characterized and developed the package insulation processes to yield an inception voltage in excess of Vrms so that transient overvoltages below this level will not damage the. The extinction voltage is above 5Vrms so that even overvoltage induced partial discharge will cease once the barrier voltage is reduced to the 5Vrms (rated) level. Older high voltage test methods relied on applying a large enough overvoltage (above rating) to break down marginal parts, but not so high as to damage good ones. Our new partial discharge testing gives us more confidence in barrier reliability than breakdown/no breakdown criteria. Isolation Barrier A A ISO5 V S +V S +5V 5V +5V 5V V S +V S ±V S ±V S 5 5 PGA 5 µf µf µf µf FIGURE. Basic Signal and Power Connections. FIGURE. Programmable-Gain Isolation Channel with Gains of,, and.

8 Isolation Barrier C pf R.5kΩ R.kΩ OPA = +V S V S C pf V S +V S µh ±V S µh µh µh ±V S µf µf µf µf µf µf µf µf FIGURE. Optional π Filter to Minimize Power Supply Feedthrough Noise; Output Filter to Remove 5kHz Carrier Ripple. For more information concerning output filter refer to AB- and AB-. This Section Repeated Times. e = V kω kω 5 +V e V = e = V V Charge/Discharge Control Multiplexer Control Section +V V e = V 5 +V 5kΩ INA5 5kΩ e 5 = V kω 5 kω V 5kΩ e 5 V = 5kΩ FIGURE 5. Battery Monitor for a V Battery Power System. (Derives input power from the battery.)

9 +5V.V REF Thermocouple R R kω +5V +5V 5V +5V 5V Isothermal Block with N () MΩ R R Ω R +In INA R G or INA In R 5 5Ω 5V Zero Adj 5 ISA TYPE 5 MATERIAL SEEBACK COEFFICIENT (µv/ C) VOUT R (R = Ω) R (R 5 + R = Ω) Ground Loop Through Conduit NOTE: ().mv/ C at.µa. E J K T Chromel Constantan Iron Constantan Chromel Alumel Copper Constantan kΩ.kΩ 5.kΩ 5.kΩ 5.kΩ.kΩ.kΩ.5kΩ FIGURE. Thermocouple Amplifier with Ground Loop Elimination, Cold Junction Compensation, and Up-scale Burn-out..mA.mA RTD (PT) R G R Z () R CM kω.ma XTR5.µF NOTE: () R Z = RTD resistance at minimum measured temperature. -ma 5 RCV 5, 5 +V +V S = 5V on PWS V V S = 5V on PWS V - 5V FIGURE. Isolated -ma Instrument Loop. (RTD shown.)

10 R S V L R D Load I L R D V+ 5 V.µF.µF 5 DCP55.µF FIGURE. Isolated Power Line Monitor..µF 5.µF.µF 5 DCP55 V+ V kω kω X Y kω OPA.µF XY MPY (V ) (V ) (V ) I L = V R S P L = V (R D + R D ) R S R D V L = V (R D + R D ) R D

11 +5V, up to ±V Swing 5V +5V Regulator MCL5.µF.µF 5V Regulator MCL5.µF.µF.µF 5 DCP55 NOTE: The input supplies can be subregulated to ±5V to reduce PSR related errors without reducing the ±V input range. FIGURE. Improved PSR Using External Regulator. V S (+5V) V S (V) + 5 INPUT RANGE (V) () to + to +5 to + INA5 Difference Amp R R 5 kω 5 In +V S (+5V) Signal Source + R S R Reference R R C () IN 5.V V S = Com V S ( 5V) NOTE: () Select to match R S. NOTE: Since the amplifier is unity gain, the input range is also the output range. The output can go to V since the output section of the ISO amp operates from dual supplies. FIGURE. Single Supply Operation of the Isolation Amplifier. For additional information refer to AB-.

12 5 DCP55.µF.µF.µF 5V, ma Input 5 V V+ INPUT SECTION OUTPUT SECTION +5V, ma Auxiliary Isolated Power Output +5V V+ V V O Output 5V V O FIGURE. Input-Side Powered ISO Amp. +5V 5 DCP55 DCP55.µF 5.µF.µF.µF.µF 5V, ma Input Auxiliary Isolated Power Output +5V, ma 5 V V+ INPUT SECTION V+ V V O OUTPUT SECTION +5V, ma Auxiliary Isolated Power Output Output 5V, ma V O FIGURE. Powered ISO Amp with Three-Port Isolation.

13 This datasheet has been downloaded from: Datasheets for electronic components.