Π-type LC filter in power supply in single chip microcomputer circuit

燕园技术宅

Π-type LC filter in power supply in single chip microcomputer circuit [Copy link]

I want to make a STM32F429 core board recently. In addition to the SDRAM EEPROM Ethernet transceiver chip circuit and the most basic minimum system circuit, the board does not plan to add an LDO power conversion circuit. The power supply of the core board is planned to be provided by the expansion circuit board with 3.3V, and the expansion circuit board is converted from 5V to 3.3V by LDO. So I want to add a Π-type LC filter to the power input of the core board, but I have never been exposed to emc and emi, so I don’t know how to determine the parameters. I only know that the cutoff frequency is more suitable at 50KHz, and I don’t know much about the choice of inductor type. I hope everyone can give me some advice on how to design to improve the purity of the power supply and improve electromagnetic compatibility. When drawing the PCB, I plan to make a four-layer board. What else should I pay attention to in order to make the core board more stable?

chunyang

MCU systems generally do not need any LC filtering circuits, capacitor decoupling is sufficient, and it is only needed in special occasions, which can only be treated in specific applications. The core board is a pure digital small signal system, and LC filtering will not bring any observable benefits to EMC characteristics. If there is an ADC in the system, it is necessary to pay attention to the ripple of the ADC power supply and reference, which often uses LDO secondary voltage regulation or even a dedicated reference source, and it is still unrelated to LC filtering.

燕园技术宅

chunyang posted on 2019-5-3 12:58 MCU system generally does not need any LC filtering circuit, capacitor decoupling is enough, it is only needed in special occasions, this can only be treated specifically for specific applications, the core board is pure...

If the working environment of the core board is relatively harsh, there is a small radio station nearby. ADC and DAC are not used in the board, only SPI IIC Ethernet and other communication functions. If a filter is to be added, do we also need to consider the ripple assignment and frequency of the power supply?

chunyang

Yanyuan Technology House published on 2019-5-3 15:37 If the working environment of the core board is relatively bad, there is a small radio station nearby. The ADC and DAC are not used in the board, only SPI IIC Ethernet and other communications...

For digital systems working in harsh electromagnetic environments, it is necessary to pay attention to the influence of long-line electromagnetic noise coupling on the logic level, mainly using TVS, discharge tubes, varistors and other energy absorption components. Why, you should think about it yourself.

燕园技术宅

chunyang posted on 2019-5-4 16:10 For digital systems working in harsh electromagnetic environments, it is necessary to pay attention to the impact of long-line electromagnetic noise coupling on logic levels, mainly using TVS and discharge...

OK, thank you for your guidance!