TIDUEM8B March   2019  – February 2021

 

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2.2.10 ISO7720

The ISO772x devices are high-performance, dual-channel digital isolators with 5000 VRMS (DW package) and 3000 VRMS (D package) isolation ratings per UL 1577. These devices are also certified by VDE, TUV, CSA, and CQC. The ISO772x devices provide high electromagnetic immunity and low emissions at low power consumption, while isolating CMOS or LVCMOS digital I/Os. Each isolation channel has a logic input and output buffer separated by a silicon dioxide (SiO2) insulation barrier. The ISO7720 device has both channels in the same direction while the ISO7721 device has both channels in the opposite direction. In the event of input power or signal loss, the default output is high for devices without suffix F and low for devices with suffix F. Through innovative chip design and layout techniques, the electromagnetic compatibility of the ISO772x devices has been significantly enhanced to ease system-level ESD, EFT, surge, and emissions compliance. The ISO772x family of devices is available in 16-pin SOIC wide-body (DW) and 8-pin SOIC narrow-body (D) packages.

To test the active energy and reactive energy accuracy of a meter, pulses are output at a rate proportional to the amount of energy consumed. A reference meter can then determine the accuracy of the electricity meter by calculating the error based on these pulses and how much energy is provided to the meter. In this reference design, pulses are output through headers for the cumulative active and reactive energy consumption. Using the ISO7720 device provides an isolated version of these headers for connection to non-isolated equipment, which is especially needed when the design is configured for one-voltage operation since the design is referenced with respect to one of the high-voltage line connections. In this design, the D package of the ISO7720 device is used, which provides an isolation voltage of 3000 VRMS for these signals. These isolated active and reactive signals can be set to have either a 3.3- or 5-V maximum voltage output by applying the selected maximum voltage output between the VCC (ISO_VCC) and GND (ISO_GND) of the isolated side.