Eliminate noise in high frequency switching applications

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#1

High-frequency switching applications are commonly used in integrated power and signal isolated devices. You may find that long cables or wires connected to the system containing the digital isolator, e.g. Texas Instruments’s ISOW7841 device can potentially pick up high frequency switching noise from the converter. This long wiring acts as a transmitter antenna and results in picking up the noise. How can we eliminate this noise?

To solve the issue, it’s required to keep the common-mode current loop as small as possible and to keep your cables as short as possible. In some cases, the design may not allow you to easily shorten your cables, or there may be a bad connection between the ground and power earth. Another way is to use common mode chokes for attenuating the common-mode noise.

The above diagram (Courtesy of TI) is an ISOW7841 design using a choke to reduce the common mode current as well as the return path loop area, indirectly reducing radiated emissions. The common-mode chokes can be inserted on the input and output power supplies or on any long cables connected to the system.