Buck converter pcb layout

The synchronous buck converter has been recognized as an isolated bias power supply in the communications and industrial markets. There are some major current differences between the buck converter and the Fly-Buck converter. We are already familiar with the switched current loop in a buck converter, as shown in Figure 1.

The input loop including the input bypass capacitor, the VIN pin, the high and low side switches, and the ground return pin carries the switching current. The loop should be optimized for mute operation to achieve the minimum trace length and minimum loop area.

Some would advocate that you need to route as you place, while others place so that the routing will follow naturally. No matter which way you prefer, the key is to get your components in the correct locations.

Many times PCB layout designers will place the components for neat and orderly spacing as opposed to the best circuit flow, and that can result in a bad buck converter layout.

Once the converter IC has been placed on the board, place the power components as close as possible to the IC:. Input Capacitor : The first critical part to place is the input capacitor, and it should be placed on the same surface layer as the IC pins that it is connected to. When this part is placed on the opposite board side, voltage noise can be created by the inductance of the via used to connect it to the IC.

Output Capacitor : As the final power component in the buck converter circuitry, the output capacitor should be close to the inductor. This will minimize the routing distance between the components to help ensure good output voltage regulation. Once the power components are on the board, place the other small-signal components of the buck converter circuit. These will include parts such as soft-start and decoupling capacitors that and not directly related to the power conversion.

These parts are sensitive to noise and should be placed as close as possible to the IC so that they can directly route into it to help reduce their noise sensitivity. A DC-DC buck converter used to design a switching power supply should have the goal of keeping inductance low for the critical paths of its routing.

This is best done by reducing the length of the paths rather than their widths. When it comes to power supply design, you should have a good understanding of the function, and a good reason to deviate from recommendations in the datasheet.

You might choose to add significantly higher capacitance if you have a rapidly changing load on the supply, for example. In addition to the input and output capacitors, a bootstrap capacitor is required for a proper operation.

The manufacturer recommends the value of 0. The last thing to choose is the connectors. There is a huge variety of connectors options available to suit every need on the market. The graduate decided to look through the Celestial library and to find the one he liked, as there was no requirement stated for connectivity, and settled on 2-pin terminal blocks from TE Connectivity to make connecting wires and testing the board easy.

Terminal blocks are also easy to source, and also other terminal block connectors with a common pinch of 2. I would have been equally happy with a USB type A connector on the output; however, the terminal block does make testing a lot easier. PCB design is where you can go wrong with a switched-mode design very quickly. When I was first learning how to design power supplies, I certainly made mistakes which caused highly unstable power supplies that would fry themselves seemingly without any reason - that reason, however, was poor board layout.

Switched-mode power supplies are unforgiving if they get into an unstable state, and will let the magic smoke escape pretty quickly as things begin to go horribly wrong.

I nput and output current loops of the first DC-DC buck converter design. For EMC purposes, the current path through the regulator should be kept as short as possible.

In this design, the output current path is too long. This will lead to additional noise, switching crosstalk and EMI problems. The current loops should be as short and wide as possible to minimise the radiated emissions. To correct the PCB layou t, my primary advice was to review the datasheet and study how current flows in the recommended layout.

The current flows in a circular pattern, without crossing back over itself, providing loops of current - rather than a scenic detour that crosses over itself. Part of this is ensuring the shortest paths from the IC to critical components such as the input and output capacitors and the inductor as mentioned before. The grounds from the capacitors should terminate as close to the ground of the regulator IC as possible, as should the positive voltage pins. I also suggested routing every trace without relying on polygons and then pouring the polygon over the top of those traces.

By routing the trace manually first, you can visualise and get a good feel for where the current path is. This is most critical on the ground net as I find many less experienced engineers will add a ground pour and assume everything is good, without looking at how their ground is connected or flowing.

The first step of the layout correction was the right component placement. The component placement was taken from the recommended datasheet layout with slight modifications to accommodate the components chosen. Component placement by following the datasheet recommended layout and design tips. The second step was to manually route all the traces, without placing polygons even ground.

Now energy is recovered from the inductor magnetic storage. During this cycle, the forward current flows from the inductance to Cout, and returns from Cout through the rectifier and back to the inductance. The AC current loops square measure the foremost essential connections in any oppressor layout. These ways take priority over all others. Their placement and routing have to be compelled to be planned initial and that they have to be compelled to be routed with short, low inductance ways see Figure 3.

The AC current return paths should be matched to the respective forward current paths as much as possible. The best way to do this is to use a full ground plane in close proximity on the next adjacent PCB layer. By minimizing the loop area and making the return path closely follow the forward current path, the opposing magnetic fields will tend to cancel each other out.

This reduces unwanted EMI. The return path should not be occupied with too many non-ground vias, which could undermine the effective copper for this path by creating openings or slots in this plane. It is also best to line up these vias, leaving wide alleyways of copper in the direction of the return path.