The role of adding inductance between STM32F103 power supplies

我本将心向明月

The role of adding inductance between STM32F103 power supplies [Copy link]

 

As the title says, why do we need to add an inductor between VBAT and VDDA as shown in the figure below, and what should the value of this inductor be?

我本将心向明月

The above picture should represent magnetic beads. 5R100M means that the resistance is 5Ω in the case of 100M. So why choose magnetic beads of this specification? What is the selection standard?

littleshrimp

You can refer to this information

AN-1368_cn.pdf (2.7 MB, downloads: 225)

2021-4-12 11:27 上传

点击文件名下载附件

okhxyyo

Does it look like an isolation effect?

bqgup

Inductors and capacitors are both filters. Capacitors block direct current and inductors block alternating current. They also prevent the current from increasing when the power is turned on.

maychang

VDDA is probably the power supply pin for the analog part of the chip, and the other pins are probably the power supply pins for the digital part of the chip. The purpose of adding this inductor may be to prevent the change of the current consumption of the digital part from affecting the operation of the analog circuit.

1nnocent

The operation of digital circuits needs to take into account the worst working conditions (that is, all the transistors inside the chip output high levels, and the power supply needs to provide a large amount of energy at this moment, and the power supply voltage may fluctuate to a certain extent). The pins connected in series with this inductor should have higher requirements for the power supply and a smaller fluctuation range. Adding this inductor can temporarily provide energy and stable voltage under the worst working conditions.

freebsder

The ground potential should be consistent without introducing noise into the digital part.

我本将心向明月

littleshrimp posted on 2021-4-12 11:27 You can refer to this information

Learned

我本将心向明月

maychang posted on 2021-4-12 12:06 VDDA is probably the power pin of the analog part of the chip, and the other pins are probably the power pins of the digital part of the chip. The purpose of adding this inductor may be to prevent the digital...

It looks like an inductor in the schematic diagram, but it is actually a magnetic bead, model number is cbw201209u050t

maychang

I originally wanted to be with the moon and published it on 2021-4-13 08:52 It looks like an inductor in the schematic diagram, but it is actually a magnetic bead, model number is cbw201209u050t

"It looks like an inductor in the schematic, but it's actually a magnetic bead."

If it is magnetic beads, then it is correct.

The question in the first post, "What should the value of this inductor be?" is solved.

huo_hu

I was misled by your VBAT. This component is connected between 3.3V and VDDA. There should be a capacitor.

我本将心向明月

huo_hu posted on 2021-4-13 09:54 I was misled by your VBAT. This component is connected between 3.3V and VDDA. There should also be a capacitor

It seems that there is no capacitor, just a ferrite bead. Why should there be a capacitor, LC filtering?

huo_hu

I originally will be with the heart towards the bright moon and published it on 2021-4-13 17:36 It seems that there is no capacitor, just a magnetic bead. Why should there be a capacitor, LC filtering?

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damiaa

Magnetic beads exhibit resistance and inductance characteristics to signals of a certain frequency.

Use ferrite beads to act as high-frequency resistors (attenuators).

It can maintain a high impedance in a fairly wide frequency range, thus achieving a filtering effect.

Ferrite beads are suitable for higher frequency filtering.

For power supply filtering, you can use an inductor. The inductor has a good filtering effect at low frequencies, so it is very suitable for power supply filtering.

This circuit mainly filters the high frequencies to prevent these signals from interfering with the normal operation of the CPU.

Some recommended circuits with CPU RF chips also add this.