How to avoid ground loop interference in power FTU?

Ground loop interference is caused by potential differences at different grounding points, forming common-mode current interference in the FTU's low-voltage system. The solution combines isolation and single-point grounding. First, an ADUM1410 digital isolator with an isolation voltage of 3kVrms is used at the communication interface to break the ground loop. The analog sampling section uses an ISO7240C analog isolation amplifier. The power system uses a DC-DC isolation module, such as the WRB2405S-3W, with an isolation voltage of 1500VDC.

For grounding design, a star-connected single-point grounding is used. All analog grounds, digital grounds, and power grounds are connected to the chassis grounding point through a 0Ω resistor or a PBZ1608E600Z0T ferrite bead. The chassis grounding uses a low-impedance copper strip with a grounding resistance of less than 0.05Ω. The cable shielding is single-point grounded at the FTU end, with the other end left floating. This solution eliminates ground loop current, improves the common-mode rejection ratio to over 80dB, and meets the IEC 61000-4-8 power frequency magnetic field immunity test.