Noise suppression technologies/case study introduction (Consumer)

Noise suppression for devices employing USB Power Delivery (2)

04/23/2021

INDEX

5. Using common mode choke coils for noise suppression

Since the high noise level on the power line and ground line causes noise to be emitted from the cable, inserting common mode choke coils before the USB connector on the output side of the DC-DC converter is likely to be effective.

figure: Using common mode choke coils for noise suppression — Insertion of common mode choke coils

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6. Confirmation of noise suppression effectiveness

We confirmed the effectiveness of common mode choke coils in curbing noise suppression on the evaluation board.
We inserted the DLW5BTM142TQ2 on the power line and ground line.
(Due to the processing conditions, we cut the power line and ground line of the cable for this evaluation.)

figure: Confirmation of noise suppression effectiveness — Common mode choke coil insertion locations

7. Noise suppression effectiveness

We confirmed that by inserting DLW5BTM142TQ2 common mode choke coils, noise was reduced by up to 10 dB in the 100~300 MHz range where the emission noise level is highest.

figure: Noise suppression effectiveness — Comparison of noise before and after insertion of common mode choke coils

8. Summary

There is concern that devices employing USB Power Delivery may emit noise that could interfere with the operation of the device or with data transfer.
The noise source is the DC-DC converter incorporated into the feed device. The noise is conducted by the power line and ground line of the feed device and emitted from the USB cable.
Insertion of common mode choke coils is an effective way to suppress this noise.