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Technical NotesThe Avago AdvantageNew Smaller and Faster Optical IsolationAmplifiers Feature 0.5% Gain Accuracy and1140 Vpeak Working VoltageIntroductionMany analog designers are familiar with differentialinstrumentation amplifiers but these will not provide theinsulation voltages to withstand high transient voltagessafely, nor the isolation to protect sensitive low voltagecontrol electronics from high voltage switching circuitsfound in power conversion applications. With a -40° to105°C operating temperature range, Avago’s miniatureACPL-C79x Precision Isolation Amplifiers target industrialautomation and instrumentation, renewable energy, andHVAC markets.Based on Avago’s proprietary optical isolation technology,sigma-delta analog-to-digital converters and chopperstabilized amplifiers, the ACPL-C79x isolation amplifiers areused for motor phase and rail current sensing, servo motordrive, switching power supply feedback isolation, DC linkvoltage monitoring, inverter current sensing and switchingpower supply feedback isolation. The ACPL-C79x highcommon-mode transient immunity of 15 kV/μs providesthe ruggedness and stability needed to accurately monitorcurrent in high-noise motor control environments.V DD1V IN+V IN-GND11234Figure 1. ACPL-C79X PackageAs shown in Figure 1, the isolation amplifiers are fullydifferential, input and output, with a gain accuracy of ±0.5%(ACPL-C79B), ±1% (ACPL-C79A), and ±3% (ACPL-C790).Operating from a single 5 V supply, the isolation amplifierseries features an excellent nonlinearity of 0.05% anda SNR of 60 dB. With a 200 kHz bandwidth and 1.6 μsresponse time, the ACPL-C79x captures transients duringshort circuit and overload conditions. The stretched SO-8package has a footprint 30% smaller than the standard DIP-8 package. When mounted on a PCB, it occupies a spacethat is a fraction of that for a Hall Effect or transformer basedisolation amplifier.I DD1+-SHIELD+-I DD28765V DD2V OUT+V OUT-GND2Key ACPL-C79x Key Features insulation voltage Motor Drive Application ExampleIn a typical motor drive application, shown in Figure 2, currentsthrough a small value current sense resistor cause a voltagedrop that is sensed by the ACPL-C79x and a differential outputvoltage, proportional to the current, is created on the outputside of the isolation barrier. A floating power supply (which inmany applications could be the same supply that is used todrive the high-side power transistor) is regulated to 5 V using from the current sensing resistor, or shunt (RSENSE), is appliedto the input of the ACPL-79x through an RC anti-aliasing filter(R5 and C3). And finally, the differential output of the isolationamplifier is converted to a ground referenced single-endedMOTOR* * *+ –RSENSEHV+HV-POSITIVEFLOATINGSUPPLYGATE DRIVECIRCUITU178L05 VDD1IN OUTC1C2 10.1 0.1F R5 F210 C347 nF 3* * *GND1***4U2ACPL-C79B/ACPL-C79A/ AACPL-C790VDD2 (+5 V)8765GND2C40.1 FR12.00 KR22.00 KC647 pFGND2C547 pFR310.0 K+15 VC80.1 FGND2–U3+ TL032AC7R410.0 K 0.1 F-15 V GND2VOUTYour Imagination, Our InnovationSense Illuminate ConnectFigure 2. Typical motor current sense circuit