| ??? 07/15/09 13:25 Modified: 07/15/09 13:28 Read: times |
#167339 - Version B, but without FB... Responding to: ???'s previous message |
Lukas said:
1) generally about the fragmented ground on the top and bottom - you answered me that it is possible so I am going to make my ground vias smaller and put them in parellel... Yes, you can connect the GND islands on top and bottom layers to the common ground plane via vias. Lukas said:
2) about the switcher's ground - I have not understood it yet, sorry. There is a PCB layout in the datasheet of LM25574 - 2 layer board with gnd plane on bottom that the switcher is connected to. But I have 4 layer board and I don't know if the inner planes could be just below the switcher because of the noise. I have found somewhere on the murate website that FB could be used at the gnd and power trace so I put them into my schematic directly behind the output capacitor and that is why two separated grounds were created - ground of the switcher and common ground... I don't know what is correct and what is adequate... As Per already mentioned version B is to be prefered, but without using the FB for connecting the different grounds. Unfortunately I have no schematic of your circuit, so I can only guess what's the circuit is doing. I guess that GND of switcher is to be connected to the common ground? Then, do it directly, without a ferrite bead, and do it best at the ground pin of output cap. Make a connection of your local (the switcher's!) ground plane to the common ground plane only near the ground pin of output cap of switcher. The reason, why the common ground plane should not be routed under the switcher is, that there's so much capacitive coupling between the layers, that the switching noise of switcher would be injected into the common ground plane. Connect the input of switcher to the rest of circuit by a ferrite bead, so that in combination with input cap an input low pass filter is formed. But keep the input cap on the switcher's ground plane. Kai |
| Topic | Author | Date |
| PCB design - ground plate... | 01/01/70 00:00 | |
| excuse... | 01/01/70 00:00 | |
| You can use a local ground plane, but... | 01/01/70 00:00 | |
| So, if I understand it well... | 01/01/70 00:00 | |
| Yes, of course, but... | 01/01/70 00:00 | |
| Yes, but... | 01/01/70 00:00 | |
| No overlap | 01/01/70 00:00 | |
| Version B, but without FB... | 01/01/70 00:00 | |
| so... | 01/01/70 00:00 | |
| PCB layout... | 01/01/70 00:00 | |
| Answers... | 01/01/70 00:00 | |
| EMC | 01/01/70 00:00 | |
| Hhm, I wouldn't do that... | 01/01/70 00:00 | |
| AC power supply | 01/01/70 00:00 | |
| ground vias | 01/01/70 00:00 | |
| Locating of vias... | 01/01/70 00:00 | |
| Thank you very much... | 01/01/70 00:00 | |
| Sideplating? Thermal vias? | 01/01/70 00:00 | |
| Stackup | 01/01/70 00:00 | |
| Not such a good idea | 01/01/70 00:00 | |
| interrupted/split planes | 01/01/70 00:00 | |
| Elaboration | 01/01/70 00:00 | |
| Thank you... | 01/01/70 00:00 | |
| Nice link, Rob! | 01/01/70 00:00 | |
| Elaboration | 01/01/70 00:00 | |
| Explanation | 01/01/70 00:00 | |
| Elaboration | 01/01/70 00:00 | |
| What you propose isn't well suited for 4 layer boards | 01/01/70 00:00 | |
Hi Kai | 01/01/70 00:00 |