Noise suppression solution example in automotive power circuits

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Noise suppression solution example in automotive power circuits [Copy link]

Various electronic devices are installed in cars. In order to generate the voltage required by each electronic device, efforts are made to develop power supply circuits. In order to make the power supply circuit more efficient, switching products are used, but this is also the root cause of noise problems. Here, we introduce noise suppression measures for power supply circuits (DC-DC converters) of automotive equipment. The countermeasures and countermeasure components introduced here are not only applicable to automobiles but also to industrial equipment, etc.

Noise Countermeasures for Automotive Equipment Power Supply Circuits (DC-DC Converters) Evaluation Model Power Supply Circuit A 12V → 5V step-down DC-DC converter is used as a model circuit for evaluation. Iin ≒ 0.3A, Iout ≒ 0.7A Switching frequency ≒ 400kHz Evaluation Model Power Supply Circuit Investigation of Noise Conditions Confirm the initial noise conditions and distinguish what kind of noise is generated. Noise measurements are performed in the following three modes. Conducted noise (150kHz-108MHz) Radiated noise (150kHz-30MHz) Radiated noise (30MHz-300MHz) Confirmation of noise conditions when no countermeasures are taken Investigation of conduction mode of problematic noise ① - Conducted noise Investigate whether the problematic source of conducted noise is common mode conduction mode or differential mode conduction mode.

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Survey of Conduction Mode of Problem Noise②——Radiated Noise (150kHz-30MHz) For radiated noise, also investigate whether the problem source is common mode conduction mode or differential mode conduction mode. (150kHz-30MHz band)

Radiated Noise Survey of Conduction Mode of Problem Noise③——Radiated Noise (30MHz-300MHz) Investigate whether the problem source of radiated noise is common mode conduction mode or differential mode conduction mode. (30MHz-300MHz band)

Radiated noise Implementation of noise suppression measures Decide the countermeasure method and check how much each of the three types of noise is reduced. Guidelines for noise suppression According to the survey results, implement the following countermeasures. Conducted noise countermeasures Implement countermeasures mainly for differential mode noise suppression →Insert LPF near the power connectorNoise suppression measures for all frequency ranges

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【Example】 Inductor: LQH5BPZ4R7NT0 + Capacitor: GCM188R71E105KA49 Radiated noise countermeasures The following method is effective as a noise countermeasure for step-down DCDC converters. → Install a magnetic shield on the circuit board...Noise countermeasures up to 20MHz → Insert a CMCC (common mode choke coil) near the power converter. Common mode noise countermeasures above 20MHz 【Example】 PLT5BPH5013R1SN → Insert LPF near the power connector Differential mode noise countermeasures above 220MHz ※ Conduction noise countermeasures can be shared

Conduction noise countermeasures can be shared Noise suppression effect ①Conduction noise

Conduction noise Noise suppression effect ②Radiated noise (150kHz-30MHz)

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Noise suppression effect ③ Radiated noise (30Mz-300MHz)

Radiated noise Summary of noise suppression measures and effects The following method is very effective as a noise suppression measure for step-down DCDC converters. Countermeasures against conducted noise → (1) Inserting an LPF near the power connector...Countermeasures against noise in all frequency ranges [Example] LQH5BPZ4R7NT0＋GCM188R71E105KA49 → (2) Inserting a CMCC near the power connector...Countermeasures against noise from 10MHz and above [Example] PLT5BPH5013R1SN Countermeasures against radiated noise → (3) Mounting a magnetic shield on the circuit board...Countermeasures against noise from 20MHz and above → (4) Noise suppression by inserting a CMCC...20MHz or higher near the power connector → (5) Noise suppression by inserting an LPF...20MHz or higher near the power connector ※ (4)(5) countermeasures can be used together with (1)(2) countermeasures

Countermeasures against radiated noise The above countermeasures have completed the noise suppression of the DC-DC converter.