EMI Suppression Filters (EMC and Noise Suppression)Noise suppression for devices employing USB Power Delivery (2)

5Using 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.

Insertion of common mode choke coils

Recommended filter

DLW5BTM series
common mode choke coil chip

The DLW5BTM series supports current levels up to 6 A and provides high impedance at frequencies up to 1 GHz, making it ideal for this application.

6Confirmation 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.)

Common mode choke coil insertion locations

7Noise 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.

Comparison of noise before and after insertion of common mode choke coils

8Summary

  • 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.

Featured common mode choke coil

DLW5BTM series

Common mode choke coils are filters that reduce common mode noise.
They do not affect signals (due to their high cutoff frequency) and are ideal for eliminating common mode noise at frequencies ranging from several megahertz to several hundred megahertz.