Some tips for PCB power wiring
The capacitance of the bypass ceramic capacitor should not be too large, and its parasitic series inductance should be as small as possible. Multiple capacitors in parallel can improve the impedance characteristics of the capacitor.
The parasitic parallel capacitance of the inductor should be as small as possible, and the distance between the solder pads of the inductor leads should be as far as possible.
Avoid placing any power or signal wiring on the ground layer.
The area of the high-frequency loop should be minimized as much as possible.
The placement of vias should not disrupt the path of high-frequency current on the ground layer.
A small common circuit on the system board requires different grounding layers, and the grounding layer of the small common circuit is connected to the power grounding layer by a single point.
The drive circuit loop from the control chip to the upper and lower field effect transistors should be as short as possible.
The power circuit and control signal circuit components of the switching power supply need to be connected to a small common ground layer, and these two ground layers are generally connected by a single point.
Y capacitors should be placed where they need to be absorbed, and the closer they are to the ground, the better, but they also need to consider the specific device structure, but there is one original side that is not far from the center ground end of Y capacitor.
- The CS pin of the control IC and the resistor between the MOS and S pole should be close to the MOS S pole, because a lower voltage is obtained on this resistor for sampling, and it is far from the MOS S pole, and the total resistance will increase and cause errors. In addition, it is also easily affected by external influences and interfered with. This also depends on the specific circuit, such as the synchronous rectification circuit UCC28950 is not like this, CS shunt resistor is very close to IC because the CS signal voltage is relatively high, the total original side is to see which side of the voltage is lower, IC’s CS side is close to which side, but in switching power supply CS resistor must be in SOM nearest ground place.
- The drive circuit should be close to the control IC, because the voltage output by IC is not very high, and the voltage output by the drive circuit is much higher than that output by the control IC, which is less affected by external factors.
- The absorption circuit resistance of the primary pole should be close to the AC input voltage end (such as after filtering +310), because resistance contains an inductance component, easy to be interfered with by external interference, and also interfere with other circuits at the same time. The resistance is far away from the switching element (such as the MOS end), and the secondary pole is resistance close to the low voltage place, such as the electrolytic negative ground place.