Some experience sharing about power supply PCB design, practical!

The power circuit is an important part of an electronic product. The quality of the power circuit design will directly affect the performance of the product. Next, 2PCB will share with you some engineers’ experience summaries on power supply PCB design, hoping it will be helpful to everyone.
Basic principles of power supply PCB layout and routing

1) Choose the correct number of layers and copper thickness.

2) In the system design layout planning, the power circuit should be as close as possible to the load circuit. In particular, the power supply of the core processor should be as close as possible. If it is far away, problems may occur with transient response and line impedance.

3) The heat dissipation loop should be as close as possible to the power circuit to reduce thermal resistance.

4) On boards with heat dissipation and convection, pay attention to the layout of large-sized passive components (inductors, large capacitors) and do not hinder the air convection of the chip and MOSFET.

Experience summary of power supply PCB design

1. When placing devices, if you encounter some relatively large capacitors or resistors together with relatively small resistors and capacitors, choose the center alignment method instead of aligning the edges. Because the pads are compensated when making the package, when welding is actually made, they are not aligned, which makes it unsightly.

2. When laying out and wiring the power chip, you should first download the data sheet for reference.

3. For the layout and wiring of the switching power supply, look for the main circuit of input and output. That is VIN, VOUT. When placing the device, it must be compact, large first and then small (the size of the device). Although it is compact, space for fan holes and copper paving must be reserved.

4. The layout is in a straight line, this is when there is ample space. Most of the wiring methods are copper laying, and a small number of them are traced. The traces should be at least 10 mil. If the 10mil trace exceeds the size of the pad, you can first walk out of the pad and then change it to 10mil.

5. The 20mil trace can carry a current of 1A, and the via hole is 10/20, which can carry a current of 1A. Note that these are theoretical values, and a certain margin must be left during actual operation. The same number of vias you place on your input loop must also be placed on your output loop.

6. Consider welding issues. If the copper skin and the pad are fully connected, when you put on the solder, the heat dissipation is faster due to the large contact area. In this way, the solder has solidified before the device is placed. Therefore, we use cross connections between Pin and copper for better soldering.

7. The feedback path, usually the FB signal of the last device, or the SENS signal, runs 20mil.

8. The power supply traces are short, straight and thick, very similar to RF.

9. The inductor in the power board part should not be routed underneath, and the middle needs to be hollowed out. Because inductance is a large source of interference. If there are multiple outputs and there are multiple inductors, they should be placed vertically between adjacent ones.

10. The capacitor must be placed close to the chip pins, so that the filtering effect is the best. The signal has to pass through the capacitor before entering the chip.

11. The via hole at the input end should be placed in front of the capacitor, the via hole at the output end should be placed behind the capacitor, and the GND via hole should be placed nearby.

12. Power supply For high-speed boards, you need to consider the issue of PI, which is the issue of power integrity. This can be measured through simulation.

13. Power supply integrity. For high-speed boards, there are also certain requirements for lamination. You can set templates according to previous experience, or use SI9000 to calculate impedance, design the lamination yourself, and then communicate with the board manufacturer to get reasonable results. .

14. Regarding the division of the power layer, the division is the core power supply of the board. What is a core power supply? It is the kind of power supply with large current and large quantity. A plane cannot be divided into more than 3 power supplies. What needs to be considered is that segmentation cannot cause current carrying bottlenecks.

15. When there are digital ground and analog ground, they need to be laid with copper separately. It is common to use zero-ohm resistors or magnetic beads for jumper connection, and add an appropriate amount of vias to avoid interference with other signals.

16. When setting up the stack, the 20H principle needs to be met, that is, the power plane is 20 mil smaller than the ground plane. If the board is large enough, it can be adjusted by 30-50 mil. And drill an appropriate amount of ground via holes in the retracted part. (Equal spacing of 100-150mil)

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