Isolation AmplifierThe HCPL-7840 isolation amplifierfamily was designed for currentsensing in electronic motor drives.In a typical implementation, motorcurrents flow through an externalresistor and the resulting analogvoltage drop is sensed by theHCPL-7840. A differential outputvoltage is created on the otherside of the HCPL-7840 opticalisolation barrier. This differentialoutput voltage is proportional tothe motor current and can be convertedto a single-ended signal byusing an op-amp as shown in therecommended application circuit.Since common-mode voltageswings of several hundred volts intens of nanoseconds are commonin modern switching invertermotor drives, the HCPL-7840was designed to ignore very highcommon-mode transient slewrates (of at least 10 kV/µs).The high CMR capability of theHCPL-7840 isolation amplifierprovides the precision andstability needed to accuratelymonitor motor current in highnoise motor control environments, providing for smoothercontrol (less “torque rippleâ€Â) invarious types of motor controlapplications.
