EMI Suppression Filters (EMC and Noise Suppression)Investigation of noise conditions

The initial noise conditions were confirmed and the types of noise were isolated.

Noise suppression policies

Measures to suppress noise are implemented as follows based on the investigation results.

Measures to suppress conducted noise

Measures were implemented that focus on the suppression of normal mode noise.
→ Insert an LPF near the power connector. (Measure to suppress noise over all frequencies)
[Example] Inductor: LQH5BPZ4R7NT0 + capacitor: GCM188R71E105KA49

Measures to suppress radiated noise

The following methods are effective measures for suppressing the noise of a step-down DC-DC converter.
→ Attach a shield to the circuit substrate. (Measure to suppress noise up to 20 MHz)

→ Insert a common mode choke coil (CMCC) immediately next to the power connector. (Measure to suppress common mode noise at 20 MHz or more)
[Example] PLT5BPH5013R1SN

→ Insert an LPF near the power connector. (Measure to suppress normal mode noise at 20 MHz or more)
*This method can be used together with the above measures to suppress conducted noise.

Effects of measures (1): Conducted noise

Effects of measures (2): Radiated noise (150 kHz to 30 MHz)

Effects of measures (3): Radiated noise (30 MHz to 300 MHz)

Summary of measures and effects

The following methods are effective measures for suppressing the noise of a step-down DC-DC converter.

Measures to suppress conducted noise

→ (1) Insert an LPF near the power connector. (Measure to suppress noise over all frequencies)
[Example] LQH5BPZ4R7NT0 + GCM188R71E105KA49

→ (2) Insert a CMCC near the power connector. (Measure to suppress noise at 10 MHz or more)
[Example] PLT5BPH5013R1SN

Measures to suppress radiated noise

→ (3) Attach a shield to the circuit substrate. (Measure to suppress noise up to 20 MHz)

→ (4) Insert a CMCC immediately next to the power connector. (Measure to suppress noise at 20 MHz or more)

→ (5) Insert an LPF near the power connector. (Measure to suppress noise at 20 MHz or more)
*Measures (4) and (5) can be used together with measures (1) and (2) above.

This completes the measures for suppressing DC-DC converter noise.

Noise suppression parts used

Swipe left or right to change screens View in landscape mode.
Category Series name
Chip inductor LQH5BPZ series
Common mode choke coil PLT5BPH series  ※1
Multilayer ceramic capacitor GCM18 series  
  • ※1:When more effective measures are required, also consider other common mode choke coils such as the PLT10HH series. Refer to the selection chart below for common mode choke coils for the power lines in vehicles.

Selection chart for common mode choke coils for power lines by vehicle grade

Click to open the PDF.