Murata Noise Suppression: Power Circuits of Vehicles

Investigation of noise conditions

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

The noise was measured for these three patterns (Figure 1, below):
        •  Conducted noise (150kHz to 108MHz)
        •  Radiated noise (150kHz to 30MHz)
        •  Radiated noise (30kHz to 300MHz)

Confirmation of noise conditions without measures to suppress noise

Investigation 1

Conduction Mode of Problematic Noise (1)
The conduction mode (common mode or normal mode) of problematic conducted noise was investigated.

Investigation 2

Conduction Mode of Problematic Noise (2)
The conduction mode (common mode or normal mode) of problematic radiated noise was also investigated (150kHz to 30MHz band).

Investigation 3

Conduction Mode of Problematic Noise (3)
The conduction mode (common mode or normal mode) of problematic radiated noise was investigated (30MHz to 300MHz band).

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

Note: This method can be used together with the above measures to suppress conducted noise.

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 10MHz or more)
            [Example] PLT5BPH5013R1SN

Measures to Suppress Radiated Noise
        •  (3) Attach a shield to the circuit substrate. (Measure to suppress noise up to 20MHz)
        •  (4) Insert a CMCC immediately next to the power connector. (Measure to suppress noise at 20MHz or more)
        •  (5) Insert an LPF near the power connector. (Measure to suppress noise at 20MHz or more)

Note: Measures (4) and (5) can be used together with measures (1) and (2) above.

Noise suppression parts used

        •  Chip inductor - LQH5BPZ series
        •  Common mode choke coil - PLT5BPH series Note: When more effective measures are required, also consider other common mode choke coils such as the PLT10HH series.
        •  Multilayer ceramic capacitor - GCM18 series

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