Original question:
[FAQ] [H] Signal Isolators with Integrated Power - Top Questions, Answered
Tool/software:
How to improve radiated emissions performance of a design based on ISOW7841 to meet CISPR 32?
The radiated emissions of a design based on ISOW7841 can be improved by many EMI optimization techniques. The application note listed below describes some of those examples to improve the radiated emissions.
| Low-Emission Designs With ISOW7841 Integrated Signal and Power Isolator (Rev. C) |
Among the suggestions made in the above application note, the most effective solution is using common-mode chokes (CMC) at both input and output power supply pins of ISOW7841 as shown in the image below.
The ferrite beads on I/O lines are optional, you can also choose to use >1kΩ resistors instead if the datarate to be supported is not very high. Please make sure all the external I/O signals are referred to the GND points after the CMC and not to ISOW7841 device GND pin. ISOW7841 GND1 & GND2 pins should stay local to device and all the external I/O signals should only refer to the GND point that is after the CMC.
The CMCs should have an impedance of >1kΩ at the frequencies where you see radiated emissions violating the CISPR 32 limits. It is best if the CMC supports >1kΩ for the entire test frequency range (30MHz to 1GHz for CISPR 32). I am listing below some of the example CMC part numbers that we recommend.
1. CMC - 200mA, 15kΩ - TDK - ACT1210-510-2P
2. CMC - 200mA, 20kΩ - TDK - ACT45B-510-2P
3. CMC - 200mA, 10kΩ - Wurth - 744235510
