Circuit board factory explains the design of high-quality printed boards Part 3

Circuit board factory explains the design of high-quality printed boards Part 3

Circuit board assembly and circuit board processing manufacturers explain high-quality printed board design Part III

2.3. Power line wiring and power filter

The general literature thinks that the power cord should be as thick as possible, which I dare not completely agree with. Only in the case of high power (the average power supply current may reach 1 a within 1 second), you must ensure sufficient power line width (in my experience, 50 mil for every 1 a of current can meet the needs of most occasions). If only to prevent signal interference, the width of the power line is not the key. Even, sometimes thinner power cord is more beneficial! The quality of power supply generally does not lie in its absolute value, but in the fluctuation and superimposed interference of power supply. Filter capacitor is the key to solve power interference! If your application does have strict requirements for power quality, don't save money on filter capacitors! Pay attention to the following when using filter capacitors:

The power input end of the whole circuit should have "total" filtering measures, and various types of capacitors should be matched with each other, "no less". At least for the digital system, there should be at least 100uf electrolysis+10uf tantalum+0.1uf chip+1nf chip. Higher frequency (100khz) 100uf electrolysis+10uf tantalum+0.47uf patch+0.1uf patch. AC simulation system: for DC and low-frequency simulation system: 1000uf | 1000uf electrolysis+10uf tantalum+1uf chip+0.1uf chip.

Every important chip should have a "set" of filter capacitors around it. For digital systems, a 0.1uf chip is generally enough. Important chips or chips with large operating current should also be connected with a 10uf tantalum or 1uf chip. The chips with the highest operating frequency (CPU, crystal oscillator) should also be connected with 10nf | 470pf or a 1nf chip. The capacitor should be as close to the power pin of the chip as possible and connected directly as possible. The smaller the capacitor, the closer it should be.

For the chip filter capacitor, the inner section (from the filter capacitor to the chip power supply pin) should be as thick as possible. It is better to use multiple thin wires side by side. With the filter capacitor to provide a low (AC) impedance voltage source and suppress AC coupling interference, the power line outside the capacitor pin (referring to the section from the main power supply to the filter capacitor) is not so important. The line width does not need to be too thick, at least it does not need to occupy a large amount of board area. In some analog systems, rc filter network is also required for power input to further suppress interference.

For systems with a wide range of operating temperatures, it should be noted that the performance of aluminum electrolytic capacitors will be reduced or even lose their filtering effect at low temperatures, and appropriate tantalum capacitors should be used instead. For example, replace 470uf aluminum with 100uf tantalum | 1000uf aluminum, or replace 100uf aluminum with 22uf sheet tantalum. Circuit board assembly and circuit board processing manufacturers explain the third part of high-quality printed board design.

Note that the aluminum electrolytic capacitor shall not be too close to the high-power heating device