® ISO176 ISO 176 Precision, Isolated OPERATIONAL AMPLIFIER FEATURES DESCRIPTION ● RATED 1500Vrms Continuous 2500Vrms for One Minute 100% TESTED FOR PARTIAL DISCHARGE ISO176 is a precision isolation amplifier incorporating an uncommitted operational amplifier for input conditioning, a novel duty cycle modulation-demodulation technique and excellent accuracy. Internal input protection can withstand up to ±30V differential without damage. The signal is transmitted digitally across a differential capacitive barrier. With digital modulation the barrier characteristics do not affect signal integrity. This results in excellent reliability and good high frequency transient immunity across the barrier. Both the amplifier and barrier capacitors are housed in a plastic DIP. ● HIGH IMR: 115dB at 50Hz ● LOW NONLINEARITY: ±0.05% ● LOW INPUT BIAS CURRENT: ±5nA max ● LOW INPUT OFFSET VOLTAGE: ±20µV ● OP AMP INPUTS PROTECTED TO ±30V ● MOD INPUT PROTECTED TO ±100V ● BIPOLAR OPERATION: VO = ±10V ● SYNCHRONIZATION CAPABILITY ISO176 is easy to use. No external components are required. A power supply range of ±4.5V to ±18V makes this amplifier ideal for a wide range of applications. ● 24-PIN PLASTIC DIP: 0.3" Wide APPLICATIONS ● INDUSTRIAL PROCESS CONTROL Transducer Isolator, Thermocouple Isolator, RTD Isolator, Pressure Bridge Isolator, Flow Meter Isolator ● POWER MONITORING ● MEDICAL INSTRUMENTATION ● ANALYTICAL MEASUREMENTS ● BIOMEDICAL MEASUREMENTS ● DATA ACQUISITION ● TEST EQUIPMENT ● POWER MONITORING ● GROUND LOOP ELIMINATION 5 Shield 1 21 MOD 2 VOUT 22 Ext Osc 4 +VS1 15 +VS2 Shield 2 OUT 24 VIN– 1 VIN+ Com2 GND1 –VS1 20 3 Com1 23 –VS2 13 14 11 10 GND2 12 International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111 Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132 © 1996 Burr-Brown Corporation PDS-1294A A Printed in U.S.A. May, 1996 SPECIFICATIONS At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ unless otherwise noted. ISO176P PARAMETER ISOLATION(1) Voltage Rated Continuous: AC DC 100% Test (AC, 50Hz) Isolation-Mode Rejection AC 50Hz DC Barrier Impedance Leakage Current ISO AMP - GAIN Gain Error(2) Gain vs Temperature Nonlinearity CONDITIONS MIN TMIN to TMAX TMIN to TMAX 1s; Partial Discharge ≤ 5pC 1500 2121 2500 1500Vrms TYP ±0.05 ±10 G=1 G=1 G=1 UNITS Vrms VDC Vrms 115 160 1014 || 6 0.8 VISO = 240Vrms, 50Hz MAX 1 dB dB Ω || pF µArms ±0.102 %FSR ppm/°C % ISO AMP - OFFSET VOLTAGE Offset vs Temperature vs Supply ±500 ±2 mV µV/°C µV/V ISO AMP - INPUT Input Resistance 200 kΩ 0.1 10 V mA µF mVp-p 100 ISO AMP - OUTPUT Voltage Range Current Drive Capacitive Load Drive Ripple Voltage ±10 ±5 OP AMP - INPUT Voltage Range Bias Current vs Temperature Offset Voltage Offset Current vs Temperature ±13 ±15 ±20 ±1.5 FREQUENCY RESPONSE Small Signal Bandwidth Slew Rate 100mV, G = 1 100mV, G = 10 100mV, G = 100 V O = ±10V, G = 10 ±5 ±5 60 60 60 0.3 POWER SUPPLIES Rated Voltage Voltage Range Quiescent Current VCC1 VCC2 kHz kHz kHz V/µs 15 ±4.5 ±18 9 7.5 TEMPERATURE RANGE Operating Storage –40 –40 V nA pA/°C µV nA pA/°C V V mA mA 85 125 °C °C NOTE: (1) All devices receive a 1s test. Failure criterion is ≥ 5 pulses of ≥ 5pX. (2) Tested as a OPA and ISO, max ±0.35% FSR. 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. ® ISO176 2 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION Supply Voltage ................................................................................... ±18V Op Amp Analog Input Voltage Range ................................................. ±VS1 External Oscillator Input ..................................................................... ±25V Signal Common 1 to Ground 1 ............................................................ ±1V Signal Common 2 to Ground 2 ............................................................ ±1V Continuous Isolation Voltage: .................................................... 1500Vrms IMV, dv/dt ...................................................................................... 20kV/µs Junction Temperature ...................................................................... 150°C Storage Temperature ...................................................... –40°C to +125°C Lead Temperature (soldering, 10s) ................................................ +300°C Output Short Duration .......................................... Continuous to Common MOD Input Voltage Range ............................................................... ±100V ELECTROSTATIC DISCHARGE SENSITIVITY VIN+ 1 24 VIN– VOUT 2 23 Com 1 –VS1 3 22 Ext OSC +VS1 4 21 MOD Shield 1 5 20 GND 1 Com 2 10 OUT 11 GND 2 12 Any 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 published specifications. 15 +VS2 14 Shield 2 13 –VS2 PACKAGE/ORDERING INFORMATION PRODUCT ISO176P PACKAGE PACKAGE DRAWING NUMBER(1) BANDWIDTH 24-Pin Plastic DIP 243-2 60kHz NOTE: (1) For detailed drawing and dimension table, please see end of data sheet, or Appendix C of Burr-Brown IC Data Book. ® 3 ISO176 TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted. ISOLATION MODE VOLTAGE vs FREQUENCY PSRR vs FREQUENCY 60 54 Max AC Rating 1k 40 PSRR (dB) Degraded Performance 100 +VS1, +VS2 –VS1, –VS2 20 Typical Performance 10 0 100 10k 1k 100k 1M 10M 100M 1 10 100 Frequency (Hz) 10k 100k 1M 100k 1M IMR vs FREQUENCY 100mA 160 10mA 140 120 IMR (dB) 1mA 1500 Vrms 100µA 10µA 100 80 240 Vrms 60 1µA 40 0.1µA 10 1 100 1k 10k 100k 1 1M 10 100 1k 10k Frequency (Hz) Frequency (Hz) SIGNAL RESPONSE vs CARRIER FREQUENCY SINE RESPONSE (10kHz) Input Voltage (V) Leakage Current (rms) ISOLATION LEAKAGE CURRENT vs FREQUENCY 0 VOUT/VIN (dB) 1k Frequency (Hz) –20dB/dec (for comparison only) 15 10 5 0 –5 –10 –20 10 5 0 –5 –40 –10 –15 fIN (Hz) 0 fC 2fC 0 3fC 20 40 60 80 100 120 140 Time (µs) fOUT (Hz) 0 fc /2 0 fC /2 0 fC /2 0 ® ISO176 4 160 180 200 Input Voltage (V) Peak Isolation Voltage Max DC Rating 2.1k TYPICAL PERFORMANCE CURVES (CONT) At TA = +25°C, VS1 = VS2 = ±15V, and RL = 2kΩ, unless otherwise noted. INPUT BIAS AND INPUT OFFSET CURRENT vs TEMPERATURE 10 5 0 –5 10 5 0 –5 –10 100 200 300 400 500 600 700 2 1 IB I OS 0 –1 –2 –40 –15 800 900 1000 –15 10 35 60 85 Temperature (°C) Time (µs) STEP RESPONSE (2kHz) 15 10 5 0 –5 –10 10 5 0 –5 –10 Input Voltage (V) 0 Input Voltage (V) –10 Input Bias and Input Offset Current (nA) 15 Input Voltage (V) Input Voltage (V) SINE RESPONSE (2kHz) –15 0 50 100 150 200 250 300 350 400 450 500 Time (µs) ® 5 ISO176 BASIC OPERATION INPUT BIAS CURRENT CANCELLATION The input stage base current of the uncommitted op amp is internally compensated with an equal and opposite cancellation current. The resulting input bias current is the difference between the input stage base current and the cancellation current. This residual input bias current can be positive or negative. ISO176 isolation amplifier comprises a precision uncommitted operational amplifier followed by an isolation amplifier. The input and output isolation sections are galvanically isolated by matched and EMI shielded capacitors. Signal and Power Connections Figure 1 shows power and signal connections. Each power supply pin should be bypassed with a 1µF tantalum capacitor located as close to the amplifier as possible. All ground connections should be run independently to a common point. Signal Common on both input and output sections provide a high-impedance point for sensing signal ground in noisy applications. Com 1 and Com 2 must have a path to ground for bias current return and should be maintained within ±1V of GND1 and GND2, respectively. When the bias current is cancelled in this manner, the input bias current and input offset current are approximately the same magnitude. As a result, it is not necessary to balance the DC resistance seen at the two input terminals. A resistor added to balance the input resistances may actually increase offset and noise. SYNCHRONIZED OPERATION ISO176 can be synchronized to an external signal source. This capability is useful in eliminating troublesome beat frequencies in multichannel systems and in rejecting AC signals and their harmonics. To use this feature, an external signal must be applied to the Ext Osc pin. ISO176 can be synchronized over the 400kHz to 700kHz range. INPUT PROTECTION The amplifier inputs of ISO176 are protected with 500Ω series input resistors and diode clamps. The inputs can withstand ±30V differential inputs without damage. The protection diodes will, of course, conduct current when the inputs are over-driven. This may disturb the slewing behavior of unity-gain follower applications, but it will not damage the op amp. The MOD input is a 200kΩ resistor and can withstand ±100V without damage. The ideal external clock signal for ISO176 is a ±4V sine wave or ±4V, 50% duty-cycle triangle wave. The Ext Osc pin of the ISO176 can be driven directly with a ±3V to ±5V sine or 25% to 75% duty-cycle triangle wave and the ISO amp’s internal modulator/demodulator circuitry will synchronize to the signal. – 0.1µF – 1µF + + 1µF 0.1µF +VS1 +VS2 5 Shield 1 22 Ext Osc 4 +VS1 15 +VS2 21 MOD Shield 2 14 2 VOUT OUT 11 24 VIN– Com2 1 VIN+ VIN+ –VS1 0.1µF GND 1 –VS1 20 3 Com 1 23 – + 1µF ® 6 RLOAD GND 2 13 FIGURE 1. Basic Connections. ISO176 –VS2 10 12 – + 1µF –VS2 0.1µF When periodic noise from external sources such as system clocks and DC/DC converters are a problem, ISO176 can be used to reject this noise. The amplifier can be synchronized to an external frequency source, fEXT, placing the amplifier response curve at one of the frequency and amplitude nulls indicated in the “Signal Response vs Carrier Frequency” performance curve. ISO176 can also be synchronized to a 400kHz to 700kHz Square-Wave External Clock since an internal clamp and filter provide signal conditioning. A square-wave signal of 25% to 75% duty cycle, and ±3V to ±20V level can be used to directly drive the ISO176. With the addition of the signal conditioning circuit shown in Figure 2, any 10% to 90% duty-cycle square-wave signal can be used to drive the ISO176 Ext Osc pin. With the values shown, the circuit can be driven by a 4Vp-p TTL signal. For a higher or lower voltage input, increase or decrease the 1kΩ resistor, RX, proportionally, e.g. for a ±4V square-wave (8Vp-p) RX should be increased to 2kΩ. The value of CX used in the Figure 2 circuit depends on the frequency of the external clock signal. CX should be 30pF for ISO176. ISOLATION MODE VOLTAGE Isolation Mode Voltage (IMV) is the voltage appearing between isolated grounds GND1 and GND2. The IMV can induce error at the output as indicated by the plots of IMV versus Frequency. It should be noted that if the IMV frequency exceeds fC/2, the output will display spurious outputs in a manner similar to that described above, and the amplifier response will be identical to that shown in the “Signal Response vs Carrier Frequency” performance curve. This occurs because IMV-induced errors behave like inputreferred error signals. To predict the total IMR, divide the isolation voltage by the IMR shown in “IMR vs Frequency” performance curve and compute the amplifier response to this input-referred error signal from the data given in the “Signal Response vs Carrier Frequency” performance curve. Due to effects of very high-frequency signals, typical IMV performance can be achieved only when dV/dT of the isolation mode voltage falls below 1000V/µs. For convenience, this is plotted in the typical performance curves for the as a function of voltage and frequency for sinusoidal voltages. When dV/dT exceeds 1000V/µs but falls below 20kV/µs, performance may be degraded. At rates of change above 20kV/µs, the amplifier may be damaged, but the barrier retains its full integrity. Lowering the power supply voltages below ±15V may decrease the dV/dT to 500V/µs for typical performance, but the maximum dV/dT of 20kV/ µs remains unchanged. 10kΩ 1µF Square-Wave In RX 1kΩ CX OPA602 Triangle Out to ISO166/176 Ext Osc FIGURE 2. Square-Wave to Triangle Wave Signal Conditioner for Driving ISO176 Ext Osc Pin. CARRIER FREQUENCY CONSIDERATIONS ISO176 amplifier transmits the signal across the ISO-barrier by a duty-cycle modulation technique. This system works like any linear amplifier for input signals having frequencies below one half the carrier frequency, fC. For signal frequencies above fC/2, the behavior becomes more complex. The Signal Response versus Carrier Frequency performance curve describes this behavior graphically. The upper curve illustrates the response for input signals varying from DC to fC/ 2. At input frequencies at or above fC/2, the device generates an output signal component that varies in both amplitude and frequency, as shown by the lower curve. The lower horizontal scale shows the periodic variation in the frequency of the output component. Note that at the carrier frequency and its harmonics, both the frequency and amplitude of the response go to zero. These characteristics can be exploited in certain applications. Leakage current is determined solely by the impedance of the barrier capacitance and is plotted in the “Isolation Leakage Current vs Frequency” curve. ISOLATION VOLTAGE RATINGS Because a long-term test is impractical in a manufacturing situation, the generally accepted practice is to perform a production test at a higher voltage for some shorter time. The relationship between actual test voltage and the continuous derated maximum specification is an important one. Historically, Burr-Brown has chosen a deliberately conservative one: VTEST = (2 x ACrms continuous rating) + 1000V for 10 seconds, followed by a test at rated ACrms voltage for one minute. This choice was appropriate for conditions where system transients are not well defined. Recent improvements in high-voltage stress testing have produced a more meaningful test for determining maximum permissible voltage ratings, and Burr-Brown has chosen to apply this new technology in the manufacture and testing of the ISO176. It should be noted that for the ISO176, the carrier frequency is nominally 500kHz and the –3dB point of the amplifier is 60kHz. Spurious signals at the output are not significant under these circumstances unless the input signal contains significant components above 250kHz. ® 7 ISO176 PARTIAL DISCHARGE When an insulation defect such as a void occurs within an insulation system, the defect will display localized corona or ionization during exposure to high-voltage stress. This ionization requires a higher applied voltage to start the discharge and lower voltage to maintain it or extinguish it once started. The higher start voltage is known as the inception voltage, while the extinction voltage is that level of voltage stress at which the discharge ceases. Just as the total insulation system has an inception voltage, so do the individual voids. A voltage will build up across a void until its inception voltage is reached, at which point the void will ionize, effectively shorting itself out. This action redistributes electrical charge within the dielectric and is known as partial discharge. If, as is the case with AC, the applied voltage gradient across the device continues to rise, another partial discharge cycle begins. The importance of this phenomenon is that, if the discharge does not occur, the insulation system retains its integrity. If the discharge begins, and is allowed to continue, the action of the ions and electrons within the defect will eventually degrade any organic insulation system in which they occur. The measurement of partial discharge is still useful in rating the devices and providing quality control of the manufacturing process. The inception voltage for these voids tends to be constant, so that the measurement of total charge being redistributed within the dielectric is a very good indicator of the size of the voids and their likelihood of becoming an incipient failure. The bulk inception voltage, on the other hand, varies with the insulation system, and the number of ionization defects and directly establishes the absolute maximum voltage (transient) that can be applied across the test device before destructive partial discharge can begin. Measuring the bulk extinction voltage provides a lower, more conservative voltage from which to derive a safe continuous rating. PARTIAL DISCHARGE TESTING Not only does this test method provide far more qualitative information about stress-withstand levels than did previous stress tests, but it provides quantitative measurements from which quality assurance and control measures can be based. Tests similar to this test have been used by some manufacturers, such as those of high-voltage power distribution equipment, for some time, but they employed a simple measurement of RF noise to detect ionization. This method was not quantitative with regard to energy of the discharge, and was not sensitive enough for small components such as isolation amplifiers. Now, however, manufacturers of HV test equipment have developed means to quantify partial discharge. VDE in Germany, an acknowledged leader in high-voltage test standards, has developed a standard test method to apply this powerful technique. Use of partial discharge testing is an improved method for measuring the integrity of an isolation barrier. To accommodate poorly-defined transients, the part under test is exposed to voltage that is 1.6 times the continuousrated voltage and must display less than or equal to 5pC partial discharge level in a 100% production test. APPLICATIONS ISO176 isolation amplifiers are used in three categories of applications: • Accurate isolation of signals from high voltage ground potentials. • Accurate isolation of signals from severe ground noise and, • Fault protection from high voltages in analog measurements. ® ISO176 8